United States. Department of the interior. {V. S. geological survey). Department of tlie interior | � | Monographs | of the I Unitednbsp;States geological survey [ Volume XV-text [plates] ] [Seal of thenbsp;department] |nbsp;nbsp;nbsp;nbsp;,

Washington ( government printing office [ 1889 4�. 2 V. text xiv, 377 pp ; plates x pp. 180 pi.

Washington | government printing office | 1889 4�. 2 V. text xiv, 377 pp; plates x pp. 180 pi.

[United States. Department of the interior. {JJ. S. geological survey). Monograph XV).

Washington | government jirinting office | 1889 4�. 2 V. text xiv, 377 pp; plates x pp. 180 pi.

[United States. Department of the interior. (JJ. S. geological survey). Monograph XV].

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United States Geological Survey

UNITED STATES GEOLOGICAL SURVEY

THE POTOMAC

Letter op transmittal.....................................................................

Introduction............................................................................... ^

Plant localities...............................................................................

Location and geology of tlie Potomac beds.........................-..........................

Location of the Potomac beds............................................................

Geology of the Potomac beds.............................................................

Geological position and origin of the lower Potomac beds..............................

D�tSCRIPTION OP the species................................................................

Cryptogams...................................................................-..........

................................................................................

Filices...........................................................................

Phanerogams............................................................................

. ...................................................................................

.................................................................................

..................................................................................

Gymnospermous fruits............................................................

Undetermined plants..................................... ...........................

Angiosperm� ........................................................................

General remarks and conclusions.................... .........................................

List of Potomac plants....................................................................

Geological aflinities of the Potomac plants....................................................

..........................................................................................

Ferns....................................................................................

Cyoads...................................................................................

Conifers..................................................................................

Angiosperms.............................................................................

Tables..................................................................................... 349

Index....................................................................................... 373

ILLUSTRATIONS.

ILLUSTRATIOXS.

LETTER OF TRANSMITTAL.

Sir: I transmit with this the manuscript and plates describing and illustrating the flora of the Potomac or Younger Mesozoic formation of Virginia.

Almost all of the material described in this memoir was obtained in the State of Virginia. A small portion was collected in Maryland, at Baltimore.

The work of collection occupied several years. A large number of localities, extending over the belt between Baltimore, Md., and Petersburg,nbsp;Va., were carefully examined, and all significant specimens were selectednbsp;from a very large amount of material. A number of the localities werenbsp;visited several times and new collections made.

The extent of ground over which the fossiliferous exposures occur and the thorough examination made entitle us to believe that the fossilsnbsp;described in this monograph give a fair idea of the unique and interestingnbsp;vegetation existing in Potomac times. This flora is uniqiie, for it apparently contains the oldest known angiosperms, and exhibits them in considerable numbers associated with numerous Jurassic tvpes, a conjunctionnbsp;not hitherto known.

Accompanying my manuscript is a series of tables, comparing the Potomac plants with previously described fossil floras. These tables were

prepared by Prof. Lester F. Ward for his own use, but he has kindly consented to permit their publication as an appendix to this memoir. Their preparation involved an immense amount of research and comparison, andnbsp;their comprehensiveness and accuracy will add greatly to the value of mynbsp;work.

Hon. J. W. Powell,

THE POTOMAC OR YOUNGER MESOZOIC FLORA.

The plants described in this memoir, with very few exceptions, were collected personally by me.

The formation from which the plants were obtained was for a long time and by most writers included in the so-called Trias of the Atlantic slope.nbsp;Prof. William B. Rogers, however, in his earliest publications on the geology of Virginia, recognized the difference between this group of strata andnbsp;most of the Mesozoic of that State. In his first publications he called thenbsp;beds Upper Secondary, and expressed the opinion that they are of aboutnbsp;the age of the English Purbeck. Later^ he asserts the possibility that theynbsp;may form a group of passage beds, comparable to theWealden. In hisnbsp;more recent writings he calls the formation Jurasso-Cretaceous.

Mr. W J McGee, of the U. S. Geological Survey, has proposed the name �Potomac� for the group, and this name will be used by me.

Nearly all the plants described in this work come from the Potomac formation in Virginia. The few exceptions were found in Maryland, andnbsp;tliese embrace all the plants not collected by myself. They will be morenbsp;particularly noticed further on.

With the exception of the Maryland fossils, all the plants which form the subject of this work were not only collected by me, but were packed.

shipped, unpacked, and worked out of the rough material with my own hands. The specimens have in consequence never passed from undernbsp;my direct supervision. The plants were collected at intervals, andnbsp;repeated visits were paid to the more important localities in order tonbsp;secure new material which might throw light on imperfect specimens previously obtained. This method of collection causes delay and imposesnbsp;much additional labor, but it has many advantages.

In the first place, the exact locality and geological horizon of a specimen can be fixed, a matter of great importance in determining the diffusion ofnbsp;species, and in the discovery of connecting links between the local floras.nbsp;In the Potomac formation, owing to the peculiar facies of some of thesenbsp;floras, connecting links are of unusual importance.

A much greater advantage is obtained in the increased number of significant parts of plants selected and in the greater opportunity afforded for the detection of new species.

When the material is collected by the person who will describe it special attention is paid to the significant portions of fossils. In the case of plant-fossils, parts with the greatest structural significance are often not as conspicuous as those with less meaning. They may also be poorly preserved.nbsp;They would be rejected in such cases by a collector unacquainted with thenbsp;science they illustrate, especially if the amount of material were large.

The circumstances attending my collection of these plant-fossils were most favorable for thoroughness of exploration and selection. The searchnbsp;for these impressions extended over several years. During the summernbsp;material was obtained from different localities, and in autumn and winternbsp;this was worked over, studied, and drawn, the drawings in all cases beingnbsp;made by myself.

It often happened in this study that a number of fragments unlike the rest were found which were too imperfect to be made out, and this lednbsp;me in several cases to make repeated visits to the same locality, in thenbsp;hope of obtaining more complete specimens of the undetermined species.nbsp;The renewed search often met with success. It will be easily seen that anbsp;collection made under such circumstances has a completeness and valuenbsp;not otherwise attainable.

The distance apart of the most remote plant localities and the number of intervening spots affording specimens give reason to think that the fossilsnbsp;obtained enable us to form a fair notion of the vegetation of that period.nbsp;This is especially fortunate, for the hitherto known flora of the oldestnbsp;Cretaceous is exceedingly scanty.

One feature of the Potomac flora at once attracts attention. This is the large number of plants confined to single localities. In many casesnbsp;this number is so great as to give the local floras a peculiar facies, which,nbsp;were it not for the connecting links, would induce one to believe that theynbsp;differ considerably in age. This localization is perhaps chiefly due to differences in the conditions attending the entombment and preservation of thenbsp;plants. At any i-ate this feature attests the richness of the flora. Thenbsp;variety within certain limits and the abundance of the vegetation mustnbsp;have been great.

The distance from Deep Bottom on James Eiver to White House Bluff on the Potomac is more than 90 miles. If we include the Marylandnbsp;localities, 50 miles must be added. The number and location of the intervening stations will appear in the account of them presently to be given.

When fossils have been collected at given localities it may easily happen that natural or artificial changes so alter the exposures that the spot yieldingnbsp;the impressions is soon concealed. The Potomac beds, owing to their wantnbsp;of coherence and the poverty of exposures in them, are especially liable tonbsp;have fossiliferous portions hidden. Then, too, plant-impressions occur innbsp;them with exceeding irregularity, at best sparingly, and in very thin layers.nbsp;It seems, then, desirable to describe with some minuteness the spots wherenbsp;plant-fossils were found.

Before beginning these descriptions it is proper to give some account of what was formerly ktiown of plant-fossils from this formation. Thenbsp;belief, before referred to, in the Triassic age of the strata now in questionnbsp;was due in part to the apparent absence of all fossils that could throw lig�htnbsp;on the subject and call for a separation of the Potomac from the oldernbsp;Mesozoic. So far as is known to me, only two persons have published anything concerning the occurrence of fossil plants in the Potomac beds ofnbsp;Virginia.

Prof. William B. Rogers, in his annual I�eports on the geology of Virginia,^ made more than forty years ago, mentions the finding of certain plant-fossils in the vicinity of Fredericksburg. He does not describe anynbsp;of them, but considers them as indicating for the Mesozoic strata at thatnbsp;town an age not far from that of the Purbeck of England.

Mr. R. C. Taylor^ gives an account of �certain fossil dicotyledonous plants in the secondary strata of Fredericksburg.� He speaks briefly ofnbsp;some of the features of the Potomac formation in the vicinity of that town,nbsp;and mentions rather vaguely the location of the plants. He says that atnbsp;his request some of the impressions were furnished to the geological societynbsp;by Mr. F. Shepherd. These seem to have been few in number and poorlynbsp;preserved. Mr. Taylor gives in his article some figures and imperfect descriptions of these fossils. The delineations are so vague that little can benbsp;learned from an inspection of them. No dicotyledons are indicated. Certain long stems of succulent plants are mentioned as appearing in the formnbsp;of hollow casts. These may be the Frenelopsis ramosissima, so abundant atnbsp;Fredericksburg. Some coniferous twigs with acicular leaves and somenbsp;ferns are figured, but they can not be specifically determined. , His figure 3nbsp;is without doubt a Scleropteris, different from the one (N. eUiptica) found bynbsp;me, being a smaller form. I have seen none of the plants mentioned bynbsp;Professor Rogers and none of those described by Mr. Taylor, and, notwithstanding persistent search, I have failed to find the locality mentioned bynbsp;the latter gentleman. It seems, from what he says, to be different from thenbsp;one which yielded me so many fossils.

The mention by Professor Rogers of the discovery of plant-fossils in the Fredericksburg beds and the account given by Mr. Taylor seem tonbsp;have attracted very little attention.

Mr. F. B. Meek many years ago made a search for fossils in the clays lying on the line of the Baltimore and Ohio Railroad between Washingtonnbsp;and Baltimore. He succeeded in finding at Baltimore a few well-preservednbsp;impressions, which are mostly those of ferns. These were subsequentlynbsp;placed in the collections of Columbia College, New York, where they nownbsp;are. Dr. J. S. Newberry kindly loaned them to me for description. An

1 A.reprint of Annual Reports on the Geology of the Virginias, 1884, pp. 7, 712.

account of them will be given in the proper place, and they will be noted as belonging to Meek�s collection of Baltimore plants. So far as I knownbsp;the only mention made hitherto of these fossils is an incidental referencenbsp;made by Dr. Newberry in his article on the Chinese Mesozoic plants collected by Pumpelly.^

Mr. P. Tyson, while State geologist of Maryland, obtained in 1859 two cycad trunks. They were found in the above-mentioned clays extending from Washington to Baltimore. One of them was found near Contee�snbsp;Station, a point on the Baltimore and Ohio Railroad two miles southwest ofnbsp;the town of Laurel, and the other near Beltsville, a station on the samenbsp;railroad a few miles nearer Washington. These trunks, now in the Museumnbsp;of the Maryland Academy of Sciences at Baltimore, are described in thisnbsp;memoir. I think no previous desci�iption has been published. They werenbsp;photographed by Mr. Tyson, and copies of the photographs were furnishednbsp;by him to a number of his correspondents. Various writers have madenbsp;reference from time to time to these trunks. Mr. Tyson, Professor Rogers,nbsp;and Prof. P. R. Uhler, of Baltimore, have regarded them as indicating thenbsp;Wealden age of the clays which afforded them. Professor Uhler firstnbsp;found the plant locality at Fredericksburg from which I collected. Henbsp;says that when he discovered the spot he collected several boxes ofnbsp;specimens and sent them to Prof Louis Agassiz, at the Museum of Comparative Zoology, Cambridge, Mass. According to Professor Uhler thesenbsp;impressions were finer than any found since at this place. I can wellnbsp;believe this, for I have observed in collecting at the Fredericksburg localitynbsp;that the plant-impressions became poorer and fewer as the stratum wasnbsp;followed in from the outcrop. I have not been able to learn what becamenbsp;of these specimens.

Professor Uhler placed a number of the plants collected here in the Museum of the Maryland Academy of Sciences, where the}'' were subsequently seen by me. They were the first that I ever saw coming from the Potomacnbsp;formation. Professor Uhler found at Baltimore also a number of plant-impressions. They came mainly from Federal Hill. Unfortunately bothnbsp;these and his Fredericksburg collections have been lost. Owing to a mis-

'Smithsomau Contributions to Knowledge, vol. XV, No. 202, 1867, pp. 119-123, PI. IX.

take, in the absence of the professor, all these specimens were sent to the World�s Exposition at New Orleans. Nothing has been heard of themnbsp;since. As the material was very fragile, and probably was badly packed,nbsp;it was no doubt ground to powder before reaching its destination.

It is much to be regretted that these impressions were lost before they had been carefully studied and described. My recollection of them is notnbsp;very distinct, but it is sufficient to enable me to say that tlie Baltimore fossils were chiefly rather delicately incised ferns, with a sphenopterid facies,nbsp;not unlike the most important plants collected by Meek.

The plants found by Professor Uhler at Fredericksburg contained certain portions �f some species that I have never been able to find myself. I especially remember an impression of the summit of a large leaf, which thennbsp;seemed to me to be a Macrotceniojjteris. From my own discoveries since, Inbsp;am now sure that it was the tip of alurge Anomommites. I have never succeeded in finding a single specimen showing the termination of the leaves ofnbsp;this plant. As Professor Uhler was kind enough to offer to place these specimens in my hands for description, I looked forward with much pleasure tonbsp;their examination. The cases above mentioned embrace, so far as I know,nbsp;all the discoveries of fossil plants hitherto made in the Potomac formation.

When I first began to search for fossils in the Potomac beds I knew of no discoveries of plant-impressions in them except those mentioned bynbsp;Professor Rogers. Judging from th� lithology and the stratigraphy ofnbsp;these beds, I was convinced that Professor Rogers was right in supposingnbsp;that they differed in age from most of the Mesozoic of Virginia. His mention of the existence of plants in the formation induced me to undertake anbsp;systematic search for plant localities. In the course of my first reconnaissance I paid a visit to Baltimore, and having learned from Professor Uhlernbsp;of the existence of Tyson�s cycad trunks and of his own collectionsnbsp;obtained at Baltimore, I made with liim a hasty examination of these fossils at the Museum of the Maryland Academy of Sciences.

Professor Uhler had not told me of his discovery of plant-impressions at Fredericksburg, but while at the museum my attention was attractednbsp;by a small collection of fossil plants unlike any that I had ever seen. Professor Uhler informed me that he had collected them at Fredericksburg, and

he was kind enough to promise to show me the spot. Under his guidance I visited this plant locality and found the exposure in the form of a smallnbsp;ledge of rock, showing an outcrop only a few feet in length. Here Inbsp;made my first collection from the Potomac strata. Among the specimensnbsp;found 'were some that appeared to he certainly dicotyledons. These plants,nbsp;and many others new and of great interest found there, induced me tonbsp;make thorough search of the spot. The*^ experience gained at Fredericksburg taught me how to look for fossils in this formation. In the course ofnbsp;several years, during which examinations were made, the number of plantnbsp;localities found and the amount of material obtained proved to be unexpectedly great.

The mode of occurrence of the plants in the Potomac formation deserves a brief general description. There is nowhere any continuous stratum affording plant-impressions. When found at any locality and on anbsp;given horizon it rarely happens that even in the immediate vicinity anynbsp;trace of the plant-bearing bed can be found. One can depend upon nothingnbsp;except what is seen on the spot to contain plants. Even this material as anbsp;rule, when followed in working, soon gives out, often suddenly and unexpectedly. In the sandy portions of the formation we find little besidesnbsp;silicified wood, and even tliis is very rare.

Lignite is abundant, but it always occurs enveloped in clay. This, when damp, is, with hardly an exception, dark gray to black. All thenbsp;determinable portions of plants occur in clay, which, as a rule, is but littlenbsp;indurated. It is usually quite plastic and tenacious. In rare cases thenbsp;material is somewhat indurated, so as to approach in nature a shale. Twonbsp;colors ai�e common in the clay; one is pale reddish brown or chocolate;nbsp;the other when damp is dark lead-gray to nearly black. The first is morenbsp;commonly the carrier of identifiable plants, but even this clay is by nonbsp;means usually fossiliferous. In many cases it is without a trace of vege-.table matter, and in others it contains nothing but small diffused bits ofnbsp;plants. The gray clay sometimes contains good impressions, but morenbsp;commonly only lignite.

Both kinds of clay occur in two forms: (1) They are found undisturbed and as originally deposited; (2) they appear disturbed, that is, torn up from

the original bed and redeposited in an irregular manner. The undisturbed clay often possesses a somewhat regular structure. It is then either laminated or cleavable, especially if plants are present. This form of the claysnbsp;gives almost all of the well-preserved specimens. These undisturbed claysnbsp;occur in more or less extended lenticular sheets that finally thin out andnbsp;disappear, showing in their course many irregularities. Often they arenbsp;found in pockets of limited extent.

The clays are commonly found disturbed. They then appear in the form of masses or small particles that have been torn up from some preexisting clay layer, transported to a greater or less distance, and depositednbsp;either singly enveloped in the sands, or together in irregular pockets andnbsp;layers mixed with some sand. If abundant, the redeposited clay particles,nbsp;when cemented together by pressure, form layers, at first sight not unlikenbsp;the undisturbed clay beds. It is easy to detect these deposits on attemptnbsp;ing to work out plant impressions occurring in them. They lack the laminated structure and cleavage of the undisturbed material. The clay isnbsp;much mixed with sand, and is confusedly heaped together, contorted, andnbsp;affected by slickensides. The contained 'fossils are very fragmentary, andnbsp;lie at any angle in the material, so that it is rarely possible to extricate themnbsp;without destroying the specimens.

In some cases the redeposited masses are large enough to retain the original comparatively regular structure, especially if they have not beennbsp;transported far. In such cases good impressions may be obtained. Innbsp;some cases a remnant of the original bed may be found covered by the disturbed clay. There is no essential difference between the plants in thenbsp;original beds and those in the redeposited clays, and hence no very longnbsp;period of time had elapsed between the deposition of the original bed andnbsp;that of the disturbed material. These confused and disturbed clays maynbsp;occur at any horizon in the Potomac, and they are common at and near itsnbsp;top. They are often mixed with coarse sand, and they even contain pebbles, sometimes of large size. It is not unusual to find one of these disturbed clays resting on a cobblestone layer.

A common mode of occurrence for the clay of both colors is in the form of isolated masses and particles imbedded in the sand. In some cases

these particles are small, and are intimately mixed with sand; in others they take the shape of rolled masses or halls of considerable size. Thesenbsp;have been seen five or six feet in diameter, but more commonly they arenbsp;only a foot or less. The balls rarely contain good impressions, for theynbsp;have generally been much crushed and contorted. They are often associated with large cobbles. The presence of these balls, and of the disturbednbsp;clays, may be taken as indicating that some change has occurred whichnbsp;increased the agitation of the waters and caused erosion to take place for anbsp;short time. Hence they indicate erosion-horizons. It is clear that thenbsp;normal deposit of the Potomac of Virginia was sand, and that the claynbsp;layers were formed only in eddies and still portions of the waters. Anynbsp;renewal of the more violent movement, continuing the transport and deposition of sand, might erode the lately deposited clay.

Lignite is very abundant in the Potomac formation, and its mode of occurrence is worthy of notice. As stated before, it occurs always imbeddednbsp;in dark gray clay. The usual form in which this material is found is thatnbsp;of single logs and limbs, or aggregations of these. The single logs, andnbsp;some of the aggregations, were plainly drift material. It is quite a commonnbsp;thing to find imbedded in the sand, and surrounded immediately by a patchnbsp;of clay, logs of lignite which now lie where they quietly settled to the bottom after floating about for a period. These represent entire trees, and thenbsp;lignite does not occur in tlie fragmentary condition in which it is alwaysnbsp;found in the so-called �iron-ore clays.� The logs occasionally have greatnbsp;length. In the cutting of the Dutch Gap Canal there was removed, as I amnbsp;informed, a lignite log forty feet long. An end of this log may still be seennbsp;in the bank of the canal, indicating a tree of the diameter of ten inches.nbsp;At least twenty feet in addition to the forty feet have been removed from it.

In several localities we find aggregations of lignite logs which appear to have been formed by the prostration of forests, the trees falling wherenbsp;they grew. In these cases the lignite logs occur lying one over the othernbsp;and nearly all having the same direction.

No plants that can be identified have been found south of James River. In the banks of the Appomattox clay occurs that seems favorable for thenbsp;preservation of plant-impressions; only small fragments, however, have

been seen in it. The fossils found in the Petersburg area were all obtained from the banks of the James Eiver below Eichmond.

Deep Bottom is the locality farthest down the James Eiver where plant-impressions have been found, and here the Potomac disappears fromnbsp;view. The spot is about four miles below the Dutch Gap Canal, beingnbsp;located in a sharp bend of the river near a group of huts A small creeknbsp;enters here after having cut a deep ravine through all the formations downnbsp;to the top of the Potomac. At this spot the river bank is composed of Quaternary, Eocene marl, and Potomac. In places the Quaternary rests on thenbsp;Potomac, but usually the Eocene bed intervenes. Just below the mouthnbsp;of the smcJl stream above liientioned a thick mass of Quaternary is seennbsp;resting on a confused mixture of materials that have the character of thenbsp;Potomac.

The greater portion of the exposure of this latter is of a rather ai'gilla-ceous gray sand, that shows all the features so common in the disturbed clay commonly found in the upper part of the Potomac. This material barelynbsp;rises above high-tide level. The argillaceous sand seems to be derived fromnbsp;the erosion of some stratum which has been torn up and had its fragmentsnbsp;confusedly redeposited. It is a structureless mass, made up of particlesnbsp;of various sizes cemented together by pressure. Embedded in this sandynbsp;matter We may find some particles more argillaceous than the main mass,nbsp;which retain to some extent the structure and cleavage of the originalnbsp;stratum. These furnish occasionally fragments of dicotyledons and othernbsp;plants of the same sort as those found elsewhere in the Potomac. The graynbsp;masses in which the plants are found are of the same general character asnbsp;the debris in which they are embedded, being simply more argillaceous.nbsp;Associated with these, and inclosed in the confused matrix, we find largenbsp;rounded masses three or four feet in diameter, of a dark chocolate tenaciousnbsp;clay, which is entirely different from the surrounding sandy matter. Thisnbsp;clay has the character of the chocolate clay so common elsewhere in thenbsp;Potomac formation. Its masses contain plant-impressions similar to thosenbsp;of the gray argillaceous sand, but they are more perfectly preserved.

A little farther down the river the top of the Potomac formation shows itself undisturbed, rising two or three feet above low tide. It is a dark tenacious clay, full of small fragments of plants. The Eocene greensand marlnbsp;rests upon it. About two hundred yards distant, in the bottom of the ravinenbsp;cut by the creek, the Potomac shows itself again undisturbed, but here onlynbsp;sand appears The spot affording the plant-impressions seems to be one ofnbsp;the erosion horizons so common in the top of the Potomac. This localitynbsp;will be referred to as � Deep Bottom.�

The next plant-bearing locality met with in ascending the river is at the lower entrance of Trent�s Reach. Trent�s Reach is the great bend in thenbsp;James River to avoid which the Dutch Gap Canal was cut. The exposuresnbsp;of the Potomac strata in this reach are extensive, but none of them are noteworthy as yielding plants, except a bluff in th� river bank diagonally opposite the lower end of the canal, and on the south side of the river. Thenbsp;spot may be located by its showing the first high bank seen on enteringnbsp;Trent�s Reach. At this place a spring branch enters the river near thenbsp;ruins of a small wharf The bank immediately at and below the wharfnbsp;contains ten to fifteen feet of the chocolate Potomac clay, but tins material,nbsp;though highly favorable for the preservation of plant-impressions, revealednbsp;none.

The high bank extends thirty or forty yards above the mouth of the branch, but the material composing it changes considerably, becoming annbsp;irregular mixture of sand and clay. This portion of the bank has suchnbsp;sudden and irregular changes of structure and material as to defy description. Most of the impressions were found about fifteen yards above thenbsp;mouth of the branch. They occur at different horizons in the bluff and sonbsp;irregularly that no description can serve as a guide for finding them. Theynbsp;may be looked for in the highest part of the Potomac, which shows aboutnbsp;fifteen feet of material, and is capped by Quaternary.

The upper portion for the thickness of three or four feet shows occasionally good impressions. The uppermost portion is quite argillaceous, in a layer four to six inches thick. This has a brownish color and contains annbsp;immense number of fragments of plants, with now and then good impressions. The fragments seem originally to have made up a large part of the

material of the layer, but now many of them have weathered out, so that the clay is very porous and is full of the cavities left by them. Mostnbsp;of these fragments are coniferous, and many belong to the species ofnbsp;Frenelopsis which is found only here. This sti'atum has yielded a numbernbsp;of interesting plants. We find in it the following, among other less noteworthy forms: Baieropsis (B. phiripartita minor'), Williamsonia, Bio�nites,nbsp;PacJiyphyllum, and Frenelopsis parceramosa.

Some portions of the material under this layer show a tendency to lamination; and here occurs a different group of plants, but they are scattered so irregularly that one can never tell where they may be found. Herenbsp;is the largest form of Baieropsis seen at Dutch Gap, viz., B.phiripartita, andnbsp;various coniferous twigs and cones, as well as several ferns. In one partnbsp;of the bluff a log was seen silicified in one portion and changed to lignitenbsp;in another. The, locality will be referred to in the description of species asnbsp;�Entrance of Trent�s Reach.�

Plant-impressions occur in both banks of Dutch Gap Canal. This canal is only about one hundred yards long. The banks are layers of sandnbsp;and clay irregularly intermixed, and varying much in thickness. The claynbsp;is in both forms, the disturbed and the undisturbed; the latter containingnbsp;most of the impressions. It has both of the characteristic colors, the graynbsp;and the reddish. In most of the bank the clay occurs in masses and pocketsnbsp;of variable thickness, apparently replacing portions of the sand. In onenbsp;portion of the right bank thin layers of dark gray clay and sand are inter-stratified. These clay layers sometimes contain very large impressions ofnbsp;Bio�nites BucJiianus, which are over a foot in length, indicating that the leafnbsp;must have been in some cases a yard long. This material is so fragile thatnbsp;it was impossible to get out specimens nearly as large as they showed themselves to be as they lay in the clay. When Bio�nites Buchiamis is abundant,nbsp;as it is here in places, very few other plants are found. The plants occurnbsp;irregularly in the sides of the canal and apparently in small pockets in thenbsp;clay. The greater portion of the material is entirely free from them.nbsp;Bio�nites Buchianus and a few ferns, with some conifers, especially of thenbsp;Sphenolepidium and Sequoia types, are the most common forms in the generalnbsp;mass of the clay.

On the right bank of the canal and in the thin interstratified layers of sand and clay a curious mode of occurrence of plants was discovered. Innbsp;examining here the clay layers, to procure as large specimens of Dio�nitesnbsp;as possible, a small mass of pale reddish plastic clay was found embedded innbsp;the interstratified sand and dark gray clay. This reddish clay seemed tonbsp;be a ball inclosed in the stratified material. It was without bedding, andnbsp;was somewhat contorted and affected with slickensides. From this it willnbsp;be seen that its lithologic character differed totally from that of the matrixnbsp;in which it was inclosed. The fossils found in it showed still greater differences, for the large impressions of Dio�nites Buchianus were lacking, andnbsp;instead there was a great variety of plants, some of which have not beennbsp;found anywhere else. A number of the species occurring in this homogeneous clay seem to have been delicate, finely incised ferns, some of whichnbsp;were beautifully preserved. This mass seems to have been a fragment tornnbsp;off from some bed of clay exceptionally rich in plants, which was subse-(|uently embedded in the interstratified sand and clay. The number andnbsp;beauty of the impressions found in it make special reference to it desirable.nbsp;It will be referred to as �Red clay ball, Dutch Gap Canal.� This clay massnbsp;was five to six feet in diameter. The locality in general will be characterized as �Dutch Gap Canal.� By this will be meant that the plants thusnbsp;referred were found in the banks of the canal, but not in the red claynbsp;ball.

Above the canal there is a reach of river about one and a half miles long. The left bank for this distance is mostly high, and composed of Q ua-ternary resting on Potomac. Most of the Potomac material is a gray,nbsp;coarse, current-bedded sand, with here and there pebbles and large claynbsp;balls. In places in the sand, nearly at high-tide level, are lenticular layers,nbsp;interrupted patches, and irregular masses of both dark gray and reddishnbsp;clay, the former predominating. These are undisturbed. Plants are foundnbsp;m several places, mostly in the lenticular layers and interrupted patches ofnbsp;gray clay. The clay is very tenacious and plastic, with indistinct cleavage. It is difficult to work out good specimens from it, notwithstandingnbsp;the undisturbed condition of the material. The plants, however, are preserved in it very perfectly.

The most important locality in this reach, and the one which has yielded the most numerous and best preserved specimens found at Dutchnbsp;Gap, is situated a few yards above a spot used by fishermen as a landingnbsp;place for their reel nets, where a small shanty is located. Where the plantsnbsp;are obtained two layers of dark gray clay occur in the base of the bluff,nbsp;a foot or so above high tide. These layers are undulating in their coursenbsp;and tend to run together. Where most distant from each other, they arenbsp;separated by eighteen inches of sand. Plants occur irregularly in bothnbsp;layers, but in the lower seam there is a portion, only two to three inchesnbsp;thick, that contains plant-impressions for a considerable distance.

This fossiliferous seam is usuall}^ found near the center of the clay layer, but it rises and falls in its course, so that it is sometimes near the top andnbsp;sometimes near the bottom. The clay layers are each about twelve inchesnbsp;thick, but they vary a good deal. .The lower layer is much the richer innbsp;impressions. The best specimens of Equisetum found in the Potomac formation occur at this spot, also very fine specimens of Dio�nites. Many conifers, especially long-leaved Sequoias, a number of ferns, good impressionsnbsp;of Baieropsis pluripartita minor, and a number of other plants may here benbsp;obtained. The locality will be referred to as � Fishing hut above Dutchnbsp;Gap Canal.�

About two hundred yards above this spot there is a pocket of dark clay in the sand, which stands at so low a level as to be covered by highnbsp;tide. This is full of leaves of JDio�nites quite well preserved, but, as isnbsp;usually the case when the Dio�nites is abundant, only few other speciesnbsp;occur. About one and a lialf miles above the canal a very large springnbsp;discharges into the river, at a place called Sailoi'�s Tavern. The clays andnbsp;sand found farther down tlie stream still continue to show themselves fornbsp;about four hundred yards above the spring in the form of an irregularnbsp;bluff. About two hundred and fifty yards above the spring a pocketnbsp;of gray clay, irregularly mixed with sandy matter, occurs at about high-tide level. This material, when it was first found, was carefully examined, and tlie impression of the posterior part of a fish was obtained fromnbsp;it. Above this point on the river no good plant-impressions were found.

These localities embrace all that are worthy of mention in the vicinity of Dutch Grap. The narrow neck of- land through which the canal is cut,nbsp;and which is known as Dutch Gap, is by river 17 miles below Richmond;nbsp;by country roads, 12 miles.

In the interval between Richmond and Fredericksburg no plant-impressions have been found, and in the immediate vicinity of the latter town only one place has yielded any notable amount of fossils. As was stated,nbsp;before, this spot was discovered by Professor Uhler.

The plant-bearing layer at 1 redericksburg, on being followed in from the outcrop, proved to be very limited in horizontal extent. The spacenbsp;from which impressions were obtained was only about fifteen feet square,nbsp;and the fossiliferous material seemed to be a lenticular pocket, apparentlynbsp;formed in an eddy in tlie waters. On the outcrop the impressions werenbsp;more numerous and better preserved than farther in. The particular layernbsp;that most abounded in vegetable matter served as a water-way, and thenbsp;long-continued seepage of water through it desti�03md much good material.

The locality now in question is situated just below Mr. Phillips�s warehouse and near the boat-house of the Fredericksburg boating club, on the right-hand side of the road descending to the steamboat landing.nbsp;When first seen by me the fossiliferous material was exposed in the formnbsp;of a small ledge of rock close to the road. The ledge was mainly composed of a gray, highly argillaceous, and very fine-grained sandstone,nbsp;graduating into sandy shale. About four feet of the material containednbsp;vegetable matter. The upper portion for about three feet contained fewnbsp;recognizable parts of plants, while it had in a layer of considerable thickness so much comminuted plant-matter that it was colored brown and rendered thinly fissile. Nearly all the good impressions occurred towards thenbsp;bottom of the mass, near its junction with a bed of cobble-stones, on whichnbsp;the fossiliferous stratum rested.

Distinct impressions were found mostly in a layer here three to five inches iu thickness, ddiis cobble-stone bed is one of the most cuilousnbsp;features of the locality. It thickened up so as to cut out in all directionsnbsp;the plant-bearing material. The cobbles are composed of Azoic rock, suchnbsp;as occurs several miles to the west of the spot, mixed with some rounded

stones of the typical Potomac sand, here having the consistency of a sandstone. The cobble-stone bed itself is very local, and is nothing but a pocket representing a local erosive horizon. Many of the stones are threenbsp;to five inches in diameter and some as much as eight to ten inches. Overnbsp;the fossiliferous stratum Quaternary deposits come, having large, partlynbsp;rounded Azoic masses in their base. On working the plant deposit andnbsp;following it in and along the outcrop it was found to thin out to the westnbsp;and north, while to the south the material continued without essential lithologic change, but lost entirely its fossils.

I made repeated visits to this place and collected largely from it. I was induced to do this because the study of each collection made knownnbsp;to me fragments that were not otherwise identifiable, while they were clearlynbsp;different from the better-preserved imprints. Unfortunately the town authorities availed themselves of the excavation I had made to get materialnbsp;for mending roads, so that no doubt a large amount of good fossiliferousnbsp;matter was wasted. The quanying operations carried on by myself andnbsp;the town finally exhausted the deposit, and the place now appears as a rectangular recess, showing in the walls little besides the Quaternary and thenbsp;cobble-stone bed. From its present aspect no one would think that anynbsp;plant impressions had ever been found there. This locality will be referrednbsp;to in the descriptions of species as � Fredericksburg.�

I have made repeated and careful search for other plant localities in the vicinity of this spot, but with no success. I found that on the samenbsp;horizon with these fossil impressions, in the immediate vicinity, the material

were so many and so sudden, that it soon became evident that there was nothing here like an extensive fossiliferous horizon. Here and there, verynbsp;locally and on different horizons, a few obscure impressions might be found,nbsp;but they in no case ever extended over more than a foot or so of spacenbsp;taken horizontally, while in thickness the material would be a mere film.

North of Fredericksburg, liowever, other localities yield plants. It may be said here that in searching for plant-impressions in the Potomacnbsp;formation there is no guide except the presence of undisturbed clay. Anynbsp;layer of this kind may contain impressions, and lienee before one can say

that no fossiliferous localities exist in a given region, he must have examined every clay layer in it. As these occur generally in small patches which in the poverty of exposures must be often hidden, it will be easilynbsp;seen that many fossiliferous spots may exist where none have been found.

Going north, the next plant locality that has been seen is on the farm of Mr. Powhatan Moncure and in its vicinity. The spot may be bestnbsp;located as follows: The Telegraph road crosses Potomac Pun about sevennbsp;miles north of Fredericksburg, at the farm of Mr. Moncure. Near the run,nbsp;and just south of it, a rather steep hill descends, and here the road is muchnbsp;washed, producing a deep gully on the right-hand side. The gully exposesnbsp;at the foot of the hill an interrupted stratum of gray clay, which restsnbsp;upon a gravel bed. .The clay is mixed with sand, and was evidently tornnbsp;up from some pre-existing layer, the particles being deposited confusedly,nbsp;sometimes in masses of considerable size. Owing to the mixed characternbsp;of the material and the very limited amount of it, it was difficult, exceptnbsp;when the fragments were large, to get out good specimens. All the claynbsp;visible was worked out. The spot is interesting for yielding one of the twonbsp;species of Sagenopteris found in the Potomac beds and for the occurrencenbsp;of several well-marked plants found also at Dutch Gap and Fredericksburg.nbsp;This locality may be designated as �Road-side near Potomac Run.�

It may be noted here that the tidal portions of the streams entering the Potomac River from Virginia are known as � creeks,� while from thenbsp;head of tide up the streams are called �runs.�

At the point on the Telegraph road above mentioned an obscure farm road diverges to enter a field. At a distance of about two hundred andnbsp;fifty yards this road deflects to approach a wooded hill. Where the roadnbsp;passes first along the base of the hill another fossiliferous stratum occurs.nbsp;This is found a few yards up the hill and within the woods. This stratumnbsp;is composed of gray shale intercalated in the sand. The material is morenbsp;indurated than we usually find the clays to be, and it is well laminated.nbsp;Lithologically it is strikingly like the fossiliferous gray shale of the Potomac found at Federal Hill, on Covington street, in Baltimore, which willnbsp;be noticed further on. The stratum is from two to three feet thick, and hasnbsp;apparently considerable horizontal extent, although no traces of it appear

on the Telegraph road. It is one of the most favorable materials known to me in the Potomac formation for the preservation of good fossils.

It is of coui�se composed of undisturbed matter, unlike that found on the road. The impressions in it are numerous and well preserved, hut Inbsp;was disappointed to find that they all belonged to a few species only. Thenbsp;plants are nearly all ferns and conifers. The ferns show close affinit}^ tonbsp;the most abundant of those collected by Meek at Baltimore, thus confirmingnbsp;tlie indications of the lithology. These plants illustrate the curious localization so common in the Potomac plants. Hardly a single species foundnbsp;here occurs in the spot on the Telegraph road, the nearest affinity beingnbsp;with certain Baltimore ferns and Dutch Gap conifers. This spot will benbsp;referred to as �Hill-side near Potomac Run.�

In the woods that contain the last-described locality an interesting occurrence of lignite is met with. The lignite is situated on a small streamnbsp;about one-fourth of a mile to the southwest of the plant-locality on thenbsp;Telegraph road. The stream exposes in its channel tlie lignite logs embedded in dark gray clay. This clay is a local deposit in the usual Potomacnbsp;sand. The lignite clearly was caused by the prostration of a forest in thenbsp;place where the trees grew. The trees may be seen for more than one hundred yards along the bed of the run, lying at different levels, and mostlynbsp;turned in the same direction. The logs are much flattened, so that a cross-section presents the form of a much elongated ellipse. Some of the trunksnbsp;appear to have been originally fully two feet in diameter.

This lignite, like all that found in the lower Potomac, seems to have originated from coniferous wood, and at this place one species of conifernbsp;appears to have furnished most if not all of the material. If we may judgenbsp;from the macroscopic character of the lignite, this tree grew in forests overnbsp;all of the Potomac terrane; for most of the lignite throughout the Potomacnbsp;of Virginia and much of that found in Maryland came from the same speciesnbsp;of tree. It seems to have had a wood of uniform and compact grain, withnbsp;numerous thin, closely-placed rings of annual gi'owth.

This lignite shows peculiar features that are characteristic of nearly all found in the Virginia Potomac. When dry, if it be split longitudinally,nbsp;the structure of the wood is beautifully shown; but if a cross-fracture be

made, it presents the features of a true jet. The fracture is conchoidal, resinous, and deep black in color The only leaf-impression seen in thenbsp;clay containing this lignite was a well-marked imprint of Scleropteris elliptica.

The next locality yielding plant-impressions found in going north is in the vicinity of Brooke station. The localities on Potomac Pun are nearnbsp;the western edge of the Potomac area. Brooke station is on the easternnbsp;edge. The area in this region is about four miles wide. Brooke stationnbsp;is on the Atlantic Coast Line Railroad, nine miles north of Fredericksburg. Ill the vicinity of Brooke the contact of the Eocene with the Potomac may be seen. The cuttings for the railroad give the exposures here ofnbsp;the plant-bearing beds. Two localities in this vicinity, a short distancenbsp;apart, have been found to yield plant-impressions. One of these occurs innbsp;a cut on the railroad at the 72d mile-post from Richmond, and the othernbsp;about one-fourth of a mile farther north and near the railroad crossing overnbsp;Acquia Creek. The Potomac formation exposed at these two places showsnbsp;marked lithologic differences, and a diversity in the plants is also found.

The cut on the railroad which exposes the fossiliferous material begins at the mile-post and extends for some distance down the railroad to thenbsp;north. The Potomac here has resting upon it a thin layer of Eocene, whichnbsp;in two places thickens up by dipping and cutting out the Potomac belownbsp;the level of the track. This thickening takes place in two narrow bands,nbsp;which represent two pre-Eocene ravines cut out of the Potomac. Theynbsp;run in a northwest and southeast direction, very nearly in accordance withnbsp;the direction of the present minor streams of the region. The Potomac material is very irregular in structure and composition. It is composed in thenbsp;main of sand, with the usual varying character and current-bedded structure, in which is found clay irregularly arranged. The clay that containsnbsp;plant-impressions is mostly disturbed and deposited in pockets and rudenbsp;layers which have no deffnite course, and in which the clay is much mixednbsp;with sand, affected with slickensides, and confusedly cemented togethernbsp;by pressure. Most of the plants seem to have been caught between thenbsp;particles of clay as they were pressed together, hence it is difficult to getnbsp;out good specimens; but in one portion of the side of the cut, on the leftnbsp;facing north, a thin irregular stratum was formed by the deposition of fine

clay. This possessed some regularity of structure and was cleavahle. It afforded a number of interesting plants beautifully preserved. Unfortunately the amount was very limited and the stratum was worked out.nbsp;As most of the clay here is lumpy and confusedly thrown together innbsp;particles of some size, the plants, although quite numerous in species, arenbsp;generally very fragmentary. The specimens occur mostly a few yardsnbsp;north of the mile-post, the best being obtained on the left hand lookingnbsp;north.

This locality is remarkable for the large number of species of dicotyledons and conifers found, and also for the number of plants occurring nowhere else. Most of the conifers and dicotyledons have apparently anbsp;more recent character than the predominant plants found at the more southern localities; but the identity in mode of occurrence, and the number ofnbsp;connecting links seen in tlie plants here, indicate that the ffoi�a of this localitynbsp;is not essentially different in age from that of the rest of the Potomac. Thisnbsp;spot will be designated as � 72d mile-post,� near Brooke. The fossils atnbsp;this place give us another illustration of the localization of many of thenbsp;Potomac plants.

As stated, the number of species occurring here is large, and several of these are very abundant. Nearly all are wanting at the locality presently to be described, while some of the most common of the species at thenbsp;latter are wanting near the mile-post.

Going down the railroad about one-fourth of a mile in a northerly direction, on the right hand side where a creek crosses the road, we find anbsp;considerable area from which the earth has been removed to make a � fill.�nbsp;This has caused an abrupt bank to be left about fifty yards from the railroad. Most of this bank is composed of the current-bedded Potomac sand,nbsp;but in the top of the bank is a stratum of gray shale about eight feet thick.nbsp;This is undisturbed material, and shows distinct stratification. Portions ofnbsp;it are sandy and coarse, but a number of thin layers are composed of finenbsp;clay, and abound in plant-impressions ; which, however, all belong to a verynbsp;few species. Most of the impressions occur near the top. By far tlie mostnbsp;abundant of the impressions are those of Saj)indoj)sis, which also abound atnbsp;the 72d mile-post The locality has been very thoroughly explored, and

very few other species have been found. A small Baieropsis occurs next in abundance. It is not found at the mile-post, but has most resemblance to anbsp;plant occurring' at Federal Hill, in Baltimore. The great number of impressions of Sapindopsis is surprising, as is also the fact that so many of thenbsp;imprints show the preservation of the same portions ; i. e., the terminal partnbsp;of the pinnate leaf

Two or three imprints of bivalve shells were found. These appear to be small Unios, and they resemble some of the Wealden Unios figured innbsp;Bunker�s �Monograph of the Wealden.�^ This spot will be referred to asnbsp;�Bank near Brooke.� The clay carrying the fossils seems to be a remnantnbsp;of an original stratum of considerable extent. It is comparable to the lowernbsp;Potomac clay over the sand in Baltimore.

Going north, the next plant locality was seen at Mr. Kaidcey�s farm, on Neabsco Run. It lies three-fourths of a mile west of the �felegraph roadnbsp;and nearly opposite the place where the road crosses the run at Mr. Kankey�snbsp;house. This is near the western margin of the Potomac area. Only sixnbsp;or eight feet of Potomac sand and clay can be seen, and the floor of Azoicnbsp;slate is visible in several places. The sand is of the usual kind. The claynbsp;that carries the fossils is dark gray and very tenacious, and it is undisturbed;nbsp;but it lies in irregular patches of limited extent. Very few species occurnbsp;here. Dio�nites BucManus is the only plant of importance. Great numbersnbsp;of its leaves occur in some portions of the clay, so that they are mattednbsp;together. Here, as at Dutch Gap, this plant, when very abundant in a clay,nbsp;seems to exclude other species. It is noteworthy that in going north fromnbsp;Dutch Gap this is the first locality where any trace of this plant occurs, andnbsp;the great number of the specimens seen at its reappearance is remarkable.

This locality deserves especial notice for the lignite found there. It occurs precisely as at Potomac Run, evidently originating in the same way,nbsp;1. e., by the prostration of a forest of coniferous trees and their subsequentnbsp;change to lignite in the place where they grew. The lignite is exposednbsp;along the channel of a small stream for some thirty or forty yards. Thenbsp;stream has very feeble erosive power, and the deposit of lignite is probablynbsp;not fully shown.

This lignite exhibits exactly the same physical character as that on Potomac Run, having the curious mingling of features of jet and true lignite with woody structure. Some of the trees, which appear to have beennbsp;three feet in diameter, are much flattened, having evidently been subjectednbsp;to great pressure. As only a few feet of material now covers these trunks,nbsp;the Potomac here must have lost largely by erosion. The locality will benbsp;referred to as �Kankey�s on Neabsco Run.�

Where the Coast Line Railroad crosses Occoquan River a long cut of considerable depth has been made to form the approach on the south side tonbsp;the bridge. This cut shows Potomac sand, with fossiliferous reddish andnbsp;gray clay in small irregular patches. In some places the floor of Azoic slatenbsp;is shown, so that here, as well as at Kankey�s, the base of the Potomac is allnbsp;that remains. The only fossil worth mentioning that occurs here is Dio-�nites Buchianus'. It is by no means so abundant as at Kankey�s, and innbsp;general the plants are very rare and fragmentary. No collection was made.

The next locality which has afforded specimens is a little south of Telegraph Station. This station is on the Coast Line Railroad, three miles north of the crossing over Occoquan River. A series of cuts made in thenbsp;Potomac sand and clay are found between the station and the river. Thenbsp;only spot in this region at which plant-impressions have been found is innbsp;a cut about one and a half miles south of the station, and towards the river.nbsp;The material exposed is Azoic slate, with Potomac sand and clay resting onnbsp;it. The clay containing plants is mostly disturbed and colored gray. Thisnbsp;has poor impressions, but in the left-hand side of the cut looking north is anbsp;pocket of rather sandy, laminated, and reddish clay, which has afforded anbsp;number of well-preserved impressions. The most important of the plantsnbsp;here is Dio�nites Buchianus. This is the farthest point north at which goodnbsp;specimens of this fossil have been obtained. Fragments of it occur at Fortnbsp;Washington and also at Baltimore, but they are few and small. A numbernbsp;of ferns, conifers, etc., occur here, giving a group of plants much like thosenbsp;found at Dutch Gap. The locality will be referred to as � Near Telegraph Station.�

White House Bluff is the end of a point which terminates on the Potomac about two miles below Mount Vernon. The bluff begins just below

White House wharf, and extends several hundred yards down the river. The material composing it is almost wholly Potomac, of which it showsnbsp;fully eighty feet. This is capped by about fifteen feet of Quaternary. Thenbsp;lowest portion of the bluff, for fifteen to twenty feet, is a coarse sand, nearlynbsp;white in color, and consolidated to a pretty firm rock. Higher the sandynbsp;matter is yellowish gray, or brownish yellow, from oxidation and from thenbsp;admixture of some colored clay. Clay layers, balls, and pockets occur onnbsp;both horizons. About sixty feet above water level is a pretty well definednbsp;layer two to four feet thick of mixed sand and disturbed clay. Thisnbsp;seems to be almost pure clay in some places, and may be detected by thenbsp;water that issues from the face of the bluff. In a number of places it contains a good many bits of plants, among which some undeterminable conifers and small fragments of Dio�nites Buchianus may be seen.

At only one place have well-preserved impressions been found, about seventy-five yards below tlie old whaiT. Here a large amount of talusnbsp;forms a steep slope up to the foot of a perpendicular bank about twentynbsp;feet high. In the base of this bank the bed above described occurs Thenbsp;material is difficult of access and collecting is dangerous, since the banknbsp;above threatens to come down upon one working at its base. The claynbsp;presents the usual structural features of the disturbed clays ; but its min-ei�al character is unusual, and not found in many of the exposiu�es of thenbsp;layer in the bhiif. It has a light buff color, and is very fine in texture andnbsp;plastic; the lumps and masses are so mixed with sand in redeposition andnbsp;so much contorted that it is not easy to obtain good specimens. The impressions of leaves are numerous, but the species of plants are few. Thenbsp;dicotyledon Sapindopsis variabilis, with pinnate leaves, so common at thenbsp;two localities near Brooke, gives nearly all the imprints. The state ofnbsp;preservation of these leaves is similar to that of those seen near Brooke,nbsp;the parts of the leaf most commonly found there being most numerousnbsp;here also. This locality will be referred to as �White House Bluff.�

Fragments of plants with some determinable parts occur at Mount Vernon, on the Potomac River, two miles above White House, and also atnbsp;Fort Washington, on the Maryland shore, about three miles east of Mount

Vernon. No prolonged search lias been made at either of these places for plant-impressions, and it is quite possible that good fossils may be found atnbsp;both. Mount Vernon is noteworthy for showing on the sand of the lowernbsp;Potomac a gray laminated ai�gillaceous material similar to that seen innbsp;Federal Hill, Baltimore. The Fort Washington bluff shows at its basenbsp;lower Potomac, consisting of sand with pockets of disturbed clay. Overnbsp;this comes upper Potomac, composed of the Variegated Clay, or so-callednbsp;�iron-ore clay,� so conspicuous in portions of Maryland. Next above wenbsp;have Eocene with impressions of marine shells; and over all. Quaternary.nbsp;The disturbed clay in the top of the lower Potomac sliows masses andnbsp;particles of various sizes embedded in the sand. Some of the larger particles retain their original lamination, and in these fragments several species of plants may be found. The most important of these are Frenelopsisnbsp;ramosissima, Bio�nites Buchianus, and an undetermined dicotyledon.

The lower part of the Potomac formation appears at Washington with the features characterizing it in Virginia. In the clays exposed in the excavation for the reservoir a few obscure fragments of leaves occur, beingnbsp;found in pale reddish clay. In the dark-gray clay, which forms pocketsnbsp;in the sand composing the greater part of the formation here, a goodnbsp;deal of lignite is found. This seems to be formed by the alteration ofnbsp;drift-wood which has accumulated in certain places.

In Virginia the Potomac formation is composed of oidy one group of beds, the lower one, which is mostly sand or sandstone, with here andnbsp;thei�e sandy clay. In these materials come irregularly subordinate stratanbsp;of more or less pure clay, containing the plants found in this formation.nbsp;In Maryland the case is different, for here we find a series of beds overlyingnbsp;the lower or sandstone member, and underlying the Eocene, which as yetnbsp;cannot be separated from the sandstone or sand member by any clearlynbsp;defined universally present features. For this reason this group is retainednbsp;in the Potomac formation, forming its upper membei�.

The Potomac formation extends from Washington to Baltimore, a distance of forty miles. In this space the lower or sand member is rarely seen, for it is too deeply buried under the upper member to be visible,nbsp;except in the lowest natural depressions and the deepest artificial excava-

tions. It possesses in Maryland the features which usually distinguish it in Virginia, except that, so far as seen in Maryland, it is never cementednbsp;together and indurated sufficiently to be called a sandstone. It is an incoherent sand of varying cliaracter, which has a current-bedded structure,nbsp;clay locally replacing the sand in various ways.,

In the city of Baltimore, on Covington and Belt streets and in other places, several feet of laminated gray shale and clay occur, interbeddednbsp;with argillaceous sand. This material shows on Covington street, at thenbsp;base of Federal Hill, a thickness for the whole mass varying from six tonbsp;twelve feet. This small group of strata, which on the whole is decidedlynbsp;argillaceous, rests on the typical sand of the lower Potomac, and forms anbsp;member of this lower formation, which, although probably once generallynbsp;present, is now in most places removed by erosion. This argillaceous portion of the lower Potomac in several places in the city, and notably onnbsp;Covington and Belt streets, has afforded some interesting plants.

On this plant-bearing material, or, in its absence, on the typical sandy material of the lower Potomac, we find resting everywhere in Maryland thenbsp;tliick mass of clay and sandy clay above mentioned, which has been callednbsp;by Mr. Tyson and Professor Rogers �the Variegated Clays.� Owing to thenbsp;common occurrence of iron ore in this group of strata, it is very commonlynbsp;called the �Iron-ore Clay.� As stated above, this formation, at least fornbsp;tile present, must be regarded as forming the upper member of tlie Potomac formation. It will in this memoir be called the �Variegated Claynbsp;Group.�

This group has not been identified in Virginia, but it may possibly be feebly represented at Mount Vernon and near Alexandria. The southernnbsp;limit so far as made out is Fort Washington. It shows itself in great forcenbsp;in the vicinity of Baltimore, and has been traced by Mr. W J McGee as farnbsp;as the head of Chesapeake Bay, where extensive exposures are shown.

How far it extends into Delaware and New Jersey and what relations it bears to the plastic clays of the latter State remain to be determined.nbsp;It is separated from the lower Potomac below by an erosion horizon, andnbsp;it IS composed certainly in part of the ruins of this group. From thenbsp;Eocene also above it is separated by an erosion horizon. So far as the

evidence goes, the indications are that the variegated clay group is of the same age as the plastic clays of New Jersey,

While showing considerable variations in mineral character and physical properties, this group, when unweathered, is mainly composed of an ash-gray to dark lead-gray plastic clay, often mixed with more or less sand.nbsp;Quite commonly much of it is a pure highly plastic clay. In the upper,nbsp;and especially the exposed portions, the iron diffused in the clay has becomenbsp;irregularly oxidized, so that spots, patches, streaks, etc, of red and yellownbsp;colors are mingled with the normal gray. From this feature the namesnbsp;�Variegated Clays� and �Mottled Clays� have been taken.

This group during a very long period has been worked locally for the iron present in it. The clay is without bedding or regular structure ofnbsp;any kind. It is much affected by slickensides, and, in short, has many ofnbsp;the features seen In the disturbed clays of the lower Potomac formation.nbsp;It has a great deal of disseminated lignite, mostly in the form of smallnbsp;fragments. Sometimes the lignite is intimately mixed with the clay, andnbsp;if the particles are very small the clay is made black by them. Thenbsp;lignite, unlike most of that of the lower Potomac, does not seem to havenbsp;been formed from the altei�ation of trees buried during the accumulationnbsp;of the clay, but appears to have been already in the form of lignite whennbsp;introduced into the clay. When we consider that the amount of lignitenbsp;in the lower Potomac is very large, and note that the Variegated Claynbsp;rests on it and is certainly partly at least made up of the ruins of thatnbsp;formation, the idea is strongly siiggested that the comminuted lignite ofnbsp;these clays comes from the fragments of the lignite logs so common innbsp;the lower Potomac

What has been said above belongs more properly to the geological portion of this memoir, but it is necessary to anticipate to this extent innbsp;order to render intelligible what will be said about the probable horizon ofnbsp;the Baltimore and other Maryland plants, whose exact geologic position hasnbsp;been left doubtful by their discoverers. Owing to the depth at which thenbsp;lower Potomac of Maryland usually occurs, the exposures, so far as found,nbsp;are few and limited in extent. Detailed search has not been made in it fornbsp;plant-impressions and but few have been found.

Between Washington and Baltimore lignite is the most important substance of organic origin found in it. The amount of this seems to be large, and it occurs, as in Virginia, in the form of logs changed to lignite in placesnbsp;where the trees were entombed. The characteristic mode of occurrence innbsp;such cases is the appearance of the material in the form of entire trunks,nbsp;which have lain undisturbed until the present time. This is very differentnbsp;from the condition in which we find the lignite of the Variegated Clays.nbsp;The lignite logs, as in Virginia, are embedded in gray clay. They occurnbsp;sometimes scattered in the sand, but each log has its patch of clay surrounding it. ITe difference between the mode of occurrence of the lignitenbsp;of the lower Potomac and that of the Variegated Clays is well shownnbsp;near Hanover, a station on the Baltimore and Ohio Railroad about fifteennbsp;miles south of Baltimore.

Near Hanover a thick mass of the Variegated Clay covers the lower Potomac. It forms the hills around the station, while the latter is barelynbsp;exposed in the beds of the largest creeks. Carbonate of iron here, and innbsp;many other places, has for a long time been undergoing concentration innbsp;the Variegated Clay, owing to concretionary processes. The result hasnbsp;been the formation of nodules and crusts of iron, which for nearly one hundred years have been obtained by open cuts. Around Hanover these pitsnbsp;are numerous and extensive, disclosing well the character and structure ofnbsp;the clay. None of them seem to have penetrated through the clay to thenbsp;lower Potomac sand below. This clay has all the irregular features of disturbed clay, that is, the material looks as if it were made up of the confusedly deposited debris formed by the erosion of older clay beds. Thenbsp;lignite, which is abundant in some places, occurs as fragments, large andnbsp;small, mixed with the clay. No entii'e logs remaining in the position innbsp;which the trees were originally entombed have been seen. The materialnbsp;was probably lignite and not wood when it was buried in the clay.

Near the station there is a considerable creek, which has cut its channel below the base of the Variegated Clays. In one place the stream has just cut down to the top of the lower Potomac sand, so as to expose a fewnbsp;feet of it. The Variegated Clay is seen to rest on the eroded top of this.nbsp;A number of isolated logs of lignite are found here also, much flattened by

pressure and embedded in clay. It is evident that these logs represent trunks of trees that settled to the bottom in eddies or reaches of water thatnbsp;remained quiescent just long enough to permit the deposition of a smallnbsp;amount of clay around the trunks. One of these logs was seen surroundednbsp;by a crust of marcasite about an inch thick, which was partially changednbsp;to limonite. This was interesting as suggesting one way in which the formnbsp;of portions of plants may be retained in limonite. The wood from whichnbsp;the lignite was pi�oduced seems to have been coniferous. Two kinds ofnbsp;wood may be detected here even by a hasty inspection. One kind is thatnbsp;which has given rise to nearly all the lignite of the Virginia Potomac;nbsp;the other was seen here for the first time. This has a coarse grain andnbsp;open texture. The rings of annual growth are thick and dense; they standnbsp;out prominently and are more durable than the material between them.nbsp;The lignite from- this kind of wood is the most common form at Hanovei�.

A recent visit to Baltimore enabled me to examine the Potomac formation there under favorable conditions. The gray shale of the lower Potomac, which at Federal Hill sliows a thickness of two or three feet resting on the sand, was found to contain a number of plant-impressions. These innbsp;some cases are specifically identical with plants from the Virginia Potomac;nbsp;in others they are nearly allied to Virginia plants, and in general characternbsp;this flora seems to be similar to that of the lower Potomac of Virginia.

Professor Uhler assisted me in collecting plants from this locality, and he informed me that several of them are specifically identical with somenbsp;of those formerly collected by liim at Baltirhore which were sent to Newnbsp;Orleans. He informed me also that among the fossils sent to the last-namednbsp;city were a number that he had collected at Federal Hill, near the localitynbsp;now in question, but at a higher level, and that they all differed from thenbsp;species obtained by us jointly. This indicates that there are in the vicinitynbsp;of Federal Hill at least two fossiliferous horizons.

Unfortunately my investigations in Baltimore do not fix the horizon of the plants collected by Mr. Meek. None of the recently obtained speciesnbsp;are identical with his, with probably one exception. The rock material ofnbsp;Meek�s specimens differs so much from the shale which fiumishes the specimens on Belt and Covington streets as to indicate a difference in horizon.

It is quite probable that Meek�s specimens come from that higher horizon which yielded fossils to Professor Uhler, from whose description it wouldnbsp;appear that they belong to the lower Potomac flora, as is the case withnbsp;Meek�s plants.

It is probable, then, that all the plant-impressions found at Baltimore belong to the lower member of the Potomac formation, none coming fromnbsp;the upper one, or the Variegated Clay.

The spot where I obtained the plants belongs to the southeast slope of Federal Hill, and is situated on Covington street, east side, seventy-fivenbsp;feet north of Cross street.

Since my visit additional collections have been made by Professor Uhler and Prof Lester F. Ward at the Covington-street locality and onnbsp;Belt street. Tliey have been placed in my hands for study, and form a portion of the plants described further on.

The Belt-street locality is on that street, next to and directly north of Ellicott�s iron furnace. It is situated two squares southeast of the Coving-ton-street locality. The fossils at both spots occur in the clay layers immediately above tlie sand of the lower Potomac, the lowest rock visible.nbsp;At the Belt-street locality Professor Uhler obtained the best specimens ofnbsp;Celastrophyllmn and Achrostichopteris that were found.

The doubt that exists as to the true horizon of the plants formerly found in Maryland arises from the fact that no one who collected them wasnbsp;aware of the existence of the lower Potomac under the Variegated Claysnbsp;and of the existence of gray clay in the top of the former, or else, if thisnbsp;fact was known, the difference in the age of the two was not perceived.

All the gray clay along the Baltimore and Ohio Railroad between Washington and Baltimore and at the latter place was supposed to belongnbsp;to the Variegated Clay group. The base of tins group seems to be formednbsp;of material derived from the erosion of the argillaceous upper portion of thenbsp;lower Potomac. There is, then, no marked difference in the compositionnbsp;of the uppermost of the lower Potomac and the lowest of the Variegatednbsp;Clay system. It follows, then, that fossils attributed by former collectorsnbsp;to the lower portion of the Variegated Clay may really come from the topnbsp;of the lower Potomac.

A great deal of excavation has been carried on in and around Baltimore, and by this means the character of the formations there has been well disclosed. Lignite is abundant, showing two very distinct modes ofnbsp;occurrence. At all horizons in the Variegated Clays, except at what hasnbsp;been generally supposed to be its base, this material occurs, as at Hanovernbsp;station, in fragments mixed irregularly with the clay. But at severalnbsp;places near the supposed base of the Variegated Clays it has been found innbsp;entire logs, either isolated or aggregated in masses. The material seems tonbsp;have been undisturbed since the change of the trees to lignite. I have notnbsp;seen these lignites, and hence can not undertake to determine positively thenbsp;formation in which they are found; but from what I have seen of the modenbsp;of occurrence of the lignite in the lower Potomac and in the Variegatednbsp;Clays, 1 feel sure that the undisturbed logs occur only in the former.

After this discussion, which is largely an anticipation of matter more proper for the geologic descrii^tion of the formation, but which is necessarynbsp;on account of the doubt attending the true horizon of the first discoverednbsp;]\1 ary land plants, we may notice tlie occurrence of Tyson�s cycad trunks.

Mr. Tyson has fortunately left in his unpublished notes some record of the finding of his cycad trunks. By Mr. Tyson and by all others theynbsp;have been attributed to the Variegated Clays, but this refei�ence is probablynbsp;not correct. He says that on May 5, 1859, he went to Latchford�s orenbsp;mine (near Contee�s) and got fragments of Saurian bones just exhumed.nbsp;They occurred, according to him, near a lignite tree about sixty feet long.nbsp;From what was said above this would seem to show that the Saurian bonesnbsp;were found in the lower Potomac clay and not in the Variegated Clay.nbsp;He also states that he went to Dr, Jenkins�s place and noted the positionnbsp;of the cycad trunks to be at or near the base of the lead-colored clays.nbsp;This statement is of importance, for the portion called by him � lead-colored clays� forms the base of the Variegated Clays. This position makesnbsp;it quite probable that the horizon of the trunks is really the upper part ofnbsp;the lower Potomac.

It should be noted that the trunks are thoroughly silicified, and it is possible that they may have been silicified in the lower Potomac sand, andnbsp;then on the erosion of this, during the deposition of the clay containing

them, they may have been introduced into the somewhat later material. I call attention to this possibility because of the almost universal change ofnbsp;wood to lignite in the lower Potomac clay. Silicified wood is rare in thenbsp;Potomac and occurs almost without exception in sandy matter.

According to Mr. Tyson�s notes, one of the trunks, but which it is impossible to say, was obtained from Dr. Jenkins�s mine near Contee�s station, and the other from Mr. Emack. The latter was obtained from hisnbsp;farm near Beltsville. It does not appear whether this was obtained fromnbsp;an iron mine or was picked up on the surface. Presumably it was foundnbsp;occurring like the one obtained from Dr. Jenkins. The use of the pluralnbsp;by Mr. Tyson seems to imply this, for while both trunks were sent tonbsp;him by Dr. Jenkins, only one was found in his mine. The location ofnbsp;Contee�s station and that of Beltsville are given in the previous mentionnbsp;of these trunks.

In tlie excavation of the clay for iron various animal fossils have been found. The ore-pits in the vicinity of Contee�s ap[)ear to have yieldednbsp;more of these than any others, and they would seem worthy of the noticenbsp;of collectors. Unfortunately little attention has been paid to the collection and preservation of these fossils. Most of the specimens have beennbsp;lost, and in the case of the few that have been preserved nothing is knownnbsp;of the pits yielding them or of the horizon on which they were found.nbsp;Some of these fossils are preserved in the Museum of the Marylandnbsp;Academy of Sciences. In the main they have not been examined bynbsp;scientific experts, and hence, if proved to come from the Variegated Clays,nbsp;they can not be used in determining its age. The fact noted by Tysonnbsp;that some of them occurred near a large undisturbed lignite tree makesnbsp;it not altogether certain that they all occur in the true Variegatednbsp;Clays.^

d�he amount of material obtained from*the different plant localities and worked over is very considerable. The area over which these localitiesnbsp;are distributed is large enough to yield a fair representation of the flora

'Since this was written Professor Marsh has obtained a large number of Dinosaurian bones from this Variegated Clay group in Maryland. He thinks they belong to Jurassic types. His discoveriesnbsp;make it plain that the first discovered animal fossils come from the Variegated Clays.

of the time of the deposition of the Potomac material. The peculiar localization of the plant-remains causes the aggregate of different speciesnbsp;collected at the various places to be unexpectedly large.

It is perhaps proper to say something concerning the plan I have adopted in depicting these plants, for all the drawings were made bynbsp;myself. The principal figures have been made of natural size, and portions have been given enlarged to show details of nervation and othernbsp;significant points. In almost every case the enlargement is two diameters;nbsp;in a very few cases, where the parts of the plant were very minute, threenbsp;diameters were required. Owing to the great saving in time and labor Inbsp;have drawn the principal figures simply in outline, the details omittednbsp;being shown in the enlarged parts. As a rule, I have not attempted tonbsp;give a fac-simile of all the accidental defects and distortions shown in thenbsp;specimens figured, but at the same time care has been taken not to introduce anything hypothetical.

It has sometimes happened tliat in removing fossils from the rock in (pxarrying, impressions were exposed that could not be taken up withoutnbsp;breaking them and diminishing the pei�fection of the specimen. Thennbsp;again, in transporting the material and in attempting to split up the rocknbsp;and work out the fossil, parts would be broken off or otherwise destroyed.nbsp;This was especially liable to happen in friable and tender material, whichnbsp;at the same time had little or no regular lamination and structure. Thesenbsp;facts justify a partial restoration in drawing some of the impressions, fornbsp;tire existing specimens do not in all cases fairly represent what has beennbsp;seen. In some cases, then, missing portions have been supplied in thenbsp;drawings where they have been at one time seen, or where it is clear fromnbsp;the parts still remaining what was the character of the missing ones.nbsp;These figures T designate as slightly restored.

In a few cases, by taking different portions of the sanre plant, it has been possible to give a restoration of the entire leaf, which would shownbsp;what were its probable shape and dimensions. This has been done in thenbsp;case of some of the dicotjdedons found at Fredericksburg. These werenbsp;found mostly in a ver}^ fragmentary condition, but the fragments werenbsp;sometimes numerous enough to show partially all portions of the leaf

These are given simply as restorations of the probable original character of the leaf.

Many of the ferns of the Potomac formation have features that cause them to resemble one another, and yet there are differences not easy tonbsp;give in words. These ditferences are perhaps too slight to justify theirnbsp;separation into distinct species, and yet they are constant and give a faciesnbsp;to the plants that appears to be worthy of delineation. I have for thisnbsp;reason thought it best to give figures of these, although it increases thenbsp;number of illustrations. The somewhat peculiar grouping of the plants ofnbsp;some localities, if the connecting links were neglected, would cause certainnbsp;local floras to appear to be different from the normal Potomac vegetationnbsp;It seems best in such cases to give figures of some at least of the widelynbsp;diffused plants which occur with the peculiar ones, even when they maynbsp;have been figured from other places.

My thanks are due to Prof Lester F. Ward for valuable assistance in collecting the fossils, in the identification of them, and in facilitating thenbsp;preparation of this memoir. I am under obligations to Dr. J. S. Newberrynbsp;for the loan of the fossils collected by Mr. Meek at Baltimore, and for permission to describe them. Prof P. R. Uhler has aided me much, facilitating my examinations in Maryland, and affording me tlie opportunity tonbsp;describe Tyson�s cycad trunks. To him I am indebted for the discoverynbsp;of the plant locality at Fredericksburg, which is the most important onenbsp;in the Potomac area.

In order to make clearer the occurrence and geologic relations of the plants described in this work, it is necessary to give some account of thenbsp;location and the general geology of the Potomac beds. In this place onlynbsp;so much will be said as is required for this purpose. A detailed accountnbsp;of the geology of the formation will be found in a monograph of the U. S.nbsp;Geological Survey, shortly to be published.

In Virginia, the Potomac or Younger Mesozoic forms the greater portion of tliose beds called by Prof. William B. Rogers, in his annual re-

ports on the geology of Virginia, the � Upper Secondary.� But Professor Rogers under this designation included the strata extending in Hanovernbsp;County from the North Anna River to the Chickahominy. This seriesnbsp;belongs almost wholly to the Older Mesozoic, or Rluetic formation. It isnbsp;true that in the vicinity of Hanover Junction the Potomac appears innbsp;some places, but it is inconspicuous.

It is to be understood that in Virginia the Variegated Clays, or upper member of the Potomac formation, has not been recognized. Tlie Potomacnbsp;of this State is the lower member. Only wlien we cross the Potomac Rivernbsp;going north is a distinction to be made between lower and upper Potomac.

The Potomac strata show themselves in disconnected areas along a narrow belt which extends from the Nottoway River twenty miles south ofnbsp;Petersburg in a northerly direction past the cities of Petersburg, Richmond, Fredericksburg, and Alexandria. This formation continues fromnbsp;Virginia into the District of Columbia and Maryland, including Baltimore.nbsp;The direction of this belt is almost due north and south until Fredericksburg is passed. Then it curves around so as to take a northeast coursenbsp;by Alexandria and Washington to Baltimore. Beyond Baltimore the lowernbsp;member has not been identified with certainty, but judging from the character of the material seen at its last exposures it is not probable that itnbsp;ends at that city. The name Potomac was selected for the formation bynbsp;Mr. McGee on account of its comparatively great development and its typical character along the Potomac River below Washington.

The belt in which the Potomac areas lie is situated just outside or east of the terrane of crystalline rocks. This, in Vii'ginia and Maryland, extendsnbsp;to the head of tide in the principal rivers. The Potomac was buriednbsp;deeply beneath the more recent deposits which form the coastal and tidewater region of the Atlantic slope, and hence it appears only where thesenbsp;have been removed by erosion. We accordingly find the exposures of thisnbsp;formation near the junction of the post-Potomac formations� with the crystalline rocks, and for the most part near the head of tide in the largestnbsp;rivers.

The exposures of the formation in the belt above mentioned are so arranged as to indicate the existence of at least four disconnected areas, all

of small width. There is, however, good reason to think that this isolation of the areas is ratlier apparent than real, and that the formation extendsnbsp;far to the east and seaward under the later deposits.

A general account only can be given here of the location and dimensions of the several Potomac areas. In this account I will begin at the north and proceed southward.

My examination of the distribution of the formation north of the Potomac River in Maryland and the District of Columbia has not beennbsp;sufficiently detailed to enable me to do more than indicate approximatelynbsp;the location of the area in which exposixres are found.

I have not made any search for Potomac strata north of Baltimore, but Mr. McGee has found the upper member, or the Variegated Clays, asnbsp;stated before, in force near the liead of Chesapeake Bay.

Prof William B. Rogers^ speaks of the Variegated Clays which occur between Washington and Baltimore as extending to Wilmington in Delaware, stating that toward Delaware, from the preponderance of ferruginous coloring, they have been called by Professor Booth the �red claynbsp;formation.� How far they extend in that direction, and what relationnbsp;these incoherent beds bear to the plastic clays of New Jersey, are pointsnbsp;that remain to be determined.

The upper member, the Variegated Clay, is shown greatly developed at Baltimore and all along the lines of the Baltimore and Ohio and Baltimorenbsp;and Potomac Railroads. The eastern limit is to be found several miles eastnbsp;of these railroads, the formation being covered in that quarter by a varyingnbsp;thickness of the Tertiary, by the Quaternary, or by the ruins of these formations.

The western limit lies some miles west of the above-mentioned railroads. The farthest point south at which the Variegated Clay member has been certainly identified is Fort Washington. Possibly it may form anbsp;poi-tion of the hills at Mount Vernon, but this member is certainly absentnbsp;beyond this point.

As stated before, the lower Potomac has not been identified north of Baltimore. Between Baltimore and Washington it is evidently generally

present under the Variegated Clays, but in most cases it is too deeply buried under the latter to be seen, except in a few spots, where erosion hasnbsp;been carried deep enough to reach it.

At Baltimore the only exposures seen are within the city limits. Baltimore is evidently near the original shore line of the Potomac waters, for at this place the Potomac abuts against hills composed of crystalline rock,nbsp;and the latter sends tongues into the Potomac terrane.

The Potomac at Baltimore has suffered much and unequally from erosion. In places the Quaternary alone is found above, resting immediately on the sands of the lower member. In other places the Variegatednbsp;Clay forms the surface, resting on this sand ; and in still others, the typicalnbsp;sand of the lower member has interposed between it and the Variegatednbsp;Clays, fossiliferous, argillaceous sand and laminated clay belonging to thenbsp;lower member.

Going south towards Washington, the lower Potomac is covered by a thick mass of the Variegated Clays. It is exposed at Relay Station, ninenbsp;miles from Baltimore. At Relay Station also the Potomac must be nearnbsp;its original western limit, for we find a high bluff of ciystalline rocknbsp;abutting against and rising much above it. The hills of crystalline rocknbsp;at Relay Station appear never to have been covered by the Potomac.

From Relay Station to Washington the Baltimore and Washington turnpike runs parallel to the Baltimore and Ohio Railroad and a mile ornbsp;more west of it. No exposures of the lower Potomac were seen on thisnbsp;pike, for this portion is covered by the Variegated Clays. The marginnbsp;must lie to the west of this road. That it is present under this clay isnbsp;shown by its occurrence at Hanover, about six miles south of Relaynbsp;Station. This point is some distance east of the western limit of the formation. These are the only points between Baltimore and Washingtonnbsp;where exposures of the lower Potomac have been seen. No detailednbsp;search, however, for exposures in this interval has been made.

At Washington, both in the city and near it, the lower member may be seen in a number of places We may, for the sake of distinction,nbsp;call the belt from Baltimore to Washington the Baltimore area. It is,nbsp;however, continuous with the Fredericksburg area of Virginia, In the

vicinity of Washington the lower Potomac is covered by the same formations as at Baltimore. Apparently nowhere north of the Potomac River does the lower Potomac constitute the surface rock; but it is buried morenbsp;or less deeply under later formations.

The case is different in Virginia. Here, in a belt extending from Washington to Fredericksburg, it occupies the surface, being in tlienbsp;vicinitv of the Potomac River alone, covered by Quaternary deposits.nbsp;Idiis indicates that in going north of the Potomac River the lowernbsp;member lies at a lower level, or else it has lost more from erosion.

Passing from the District of Columbia into Virginia, we find a connected area of lower Potomac rock, which forms the surface in a narrow belt that extends to a point five miles south of Fredericksburg, wlierenbsp;tlie Massaponax River enters the Rappahannock. This may be called thenbsp;Fredericksburg area. It is the only region in which the lower Potomacnbsp;comes to the surface over an area of considerable extent. It forms a beltnbsp;on an average three or four miles wide, having its western margin nearnbsp;the Telegraph road and its eastern near the Potomac River. The Telegraph road is a dirt road, which runs from Alexandria to Fredericksburgnbsp;and beyond, crossing the principal streams which flow into the Potomacnbsp;Ri ver near the head of tide in them. The margin of the lower Potomacnbsp;keeps, for tlie most part, about a mile west of this road after Alexandrianbsp;is left.

Since the upper or Variegated Clay member of the formation is absent in Virginia, the prefix lower may be omitted in giving an account of the formation in this State; Potomac formation being here equivalent tonbsp;lower Potomac.

Along tlie Potomac River the principal exposures of the Potomac formation are to be seen on the Virginia shore and in the high points that make down to the river between the creeks. Thus we find extensive exposuresnbsp;at Mount Vernon, White House Point, Freestone Point, Shipping Point,nbsp;Cockpit Point, and near the mouth of Acquia Creek. In many places,nbsp;however, along the Potomac River, where we would expect to find the formation in question, erosion prior to the deposition of the Quaternary hasnbsp;cut it away to below water level, so that we find the banks of the river

composed of Quaternaiy material. In some places tins is wholly composed of the rnins of the Potomac beds, deposited with but little sorting and modification. In these places it is sometimes difficult to distinguishnbsp;the Quaternary from the Potomac. This is the case in High Point, nearnbsp;the mouth of Occoquan River, where for a long distance the banks of thenbsp;Potomac River are formed of Quaternary. Professor Rogers, in his annualnbsp;reports, makes this material Potomac.

The exposures of Potomac beds on the Maryland shore are much fewer than on the Virginia side. This shore, lying farther east in tlie direction of the declination of the beds, contains them at lower level. Thenbsp;formation may be seen barely exposed at Fort Washington, while farthernbsp;down the river, at Indian Head, diagonally above High Point and on thenbsp;opposite side of the river, a thickness of fully eighty feet is shown.

Along tlie P6tomac River on both sides, as everywliere else, the formation has lost greatly by erosion, and the amount thus lost is very unequal in different places. It is impossible to say when this erosion tooknbsp;place, but it is clear that much of it occurred prior to the deposition of thenbsp;Eocene. The result has been to leave the formation with an exceedinglynbsp;irregular surface, and to remove it entirely from considerable areas.

Perhaps the greatest thickness of Potomac exposed at a single locality is to be found on Acquia Creek, about two miles above the point where thenbsp;Atlantic Coast Line Railroad crosses it. Here a high hill shows the formation rising to the height of one hundred and forty feet above the water.nbsp;The character of the material is well exposed by quarries It is mostly anbsp;coarse gritty sand of light color, which is generally consolidated to a prettynbsp;firm sandstone. In some places we find a good many pebbles, and sometimes a curious mixture of these and clay balls with coarse sand. Littlenbsp;intercalated clay is found here. From Acqnia Creek to near Qnantico thenbsp;Potomac, although occurring a little back from the river, is mostly wanting in its banks, Quaternary taking its place. At Quantico and Shippingnbsp;Point only about twenty feet is to be seen. Cockpit Point, about twonbsp;miles north of this last, shows fully sixty feet of very varying material.

At Freestone Point there is a long deep railroad cut, which shows that here the Potomac is over one hundred feet thick, composed of heteroge-

nous matter. Indian Head, a few miles above Indian Point, sliows much the greatest exposure of the Potomac seen on the Maryland side. Thenbsp;rock here has the same irregular structure and mixture of materials as is tonbsp;be seen in the cut at Freestone, but the proportion of light colored sand isnbsp;much smaller. It is covered here by Eocene, and the Variegated Clay isnbsp;wanting. Indeed, as stated before, this group has not been seen anywherenbsp;south of Fort Washington. Grunsen�s Creek is the estuary of the unitednbsp;creeks Pohick and Accotink. On its south and north shores near itsnbsp;mouth are extensive exposures of tlie Potomac.

On the south side, near Gunsen�s Landing, fully seventy-five feet of sand and clay appear, having the same general character as in Indiannbsp;Head. We see here a graduation of the normal sand of the Potomac intonbsp;a greenish sandy clay, which is sometimes mottled with red. The samenbsp;thing in a more striking form is seen at Cockpit Point. Some fragmentsnbsp;of lignite, but no impressions of plants, were seen at Indian Head andnbsp;near Gunserfs Landing.

On the north shore of Gunsen�s Creek, White House Point forms a high bluff, called White House Bluff, immediately on the river. Here wenbsp;may see fully eighty feet of Potomac sand and clay, capped b}^ some tennbsp;feet of Quaternary. Tliis material is sufficiently described in the noticenbsp;of the occurrence of the plants at this place. It is strikingly differentnbsp;from the Potomac shown on the south side of the creek only a short distance away. We find here a good illustration of the unequal erosion tonbsp;which the formation has been subjected.

At the upper and lower ends of the exposure of the Potomac, points not a half a mile apart, the Quaternary forms the river bank to belownbsp;water level. It may be seen rising towards the central portioti of the bluffnbsp;until fully eighty feet of Potomac is exposed beneath it. As no Variegated Clay or Eocene can be detected in this bluff, it would appear thatnbsp;It was not submerged until Quaternary times, or else these formationsnbsp;have been removed by erosion.

Two miles above White House the Potomac again appears in the high shore on which the Mount Vernon mansion is situated. It shows here sixnbsp;to eight feet of the light-colored grit which forms the lower portion of White

House Bluff. Over tins lies about twenty feet of laminated sandy gray shale, which appears to correspond to the similarly placed material atnbsp;Federal Hill, Baltimore, which has been mentioned as containing plant-fossils.

Between White House and Mount Vernon the Quaternary occupies the river bank for most of tlie way. Fort Washington, on the Marylandnbsp;shore, is a little north of east from Mount Vernon and about four milesnbsp;distant. This place is interesting as showing in the same vertical exposurenbsp;all the formations associated with the Potomac. For a very limited spacenbsp;the Lower Potomac sand with its included clays may be seen, showingnbsp;only a few feet in thickness. Resting upon this, in the order ascending, wenbsp;have the Variegated Clay, the Eocene, and the Quaternary. From thisnbsp;point to Washington, about fourteen miles, the Potomac is mostly cutnbsp;away, and the Quaternary is along the stream the principal visible rock.

It will be seen from this account that the most easterly exposures of the formation in question are confined to the immediate vicinity of thenbsp;Potomac River. It is not to be supposed that the eastern limit of thesenbsp;beds is to be found anywhere near this river. The character of the material shown in the most eastern localities where the formation is exposednbsp;would lead us to suppose that at these places we are still far from the truenbsp;eastern margin of the formation. Strangely enough, we find in some ofnbsp;the most eastern exposures the maximum thickness of the formation, thenbsp;greatest amount of coarse material, and the most irregular structure.nbsp;Indeed, if we were to judge from the lithologic and structural featuresnbsp;alone, we would be inclined to think that the material came from the eastnbsp;and not from the west.

In this area, as in all others, no strikes and dips can be made out for the Potomac beds. It is clear that the formation as a whole declines tonbsp;the southeast. As from Washington to the mouth of Acquia Creek thenbsp;general course of the Potomac River is southwest, the declination of thenbsp;formation is nearly at right angles to its direction, and on the Marylandnbsp;side it would be soon carried beneath the plane of erosion. Near thenbsp;mouth of Acquia Creek the Potomac River bends due east and entersnbsp;more and more deeply the Tertiary terrane. Hence the last exposures ofnbsp;the Potomac formation on it occur near the mouth of that creek.

It is not necessary to give descriptions of the Potomac formation as exposed in the central and western portions of the area Tlie account given of the strata at the several plant localities will give an idea of its variablenbsp;character. It may be stated generally that along the western margin therenbsp;is a larger proportion of argillaceous matter than in the eastern outcrops.nbsp;The clayey matter shows also a greater tendency to assume various colors,nbsp;due to oxide of iron, and much of it is mottled. These features are seennbsp;more especially in the upper portions of the formation.

At Fredericksburg the western margin is found about two miles west of the town. It bends around so as to strike the Rappahannock near thenbsp;mouth of the Massaponax River. Here the Eocene lies above it, and thisnbsp;is the southern termination of exposures in the Fredericksburg area.

From the mouth of the Massaponax to tlie vicinity of Hanover Junction no Potomac has been seen. Hanover Junction is the point of crossing of the Atlantic Coast Line, and the Chesapeake and Ohio Railroads. It is situated in the triangle formed by the North Anna and the South Annanbsp;Rivers, near their junction. The material exposed in this interval is mainlynbsp;a tliick mass of sands and sandy clays, very variable in composition andnbsp;color. The name Appomattox is proposed for it, from its great development in typical form in the vicinity of the Appomattox River. It isnbsp;younger than the Miocene, for it rests on the eroded surface of this, butnbsp;being witliout fossils, its exact age can not be fixed. It is probable that nonbsp;exposures of tlie Potomac can be found between tlie points mentionednbsp;above, because the erosive power of the streams in the belt where outcrops may be looked for is not sufficient to remove the thick covering ofnbsp;superjacent material. The only streams of any size are the upper watersnbsp;of the Mattapony. None of these cut through the Eocene.

In the vicinity of Hanover Junction the Potomac shows in several places a few feet of strata. It has evidently lost much by erosion. In thenbsp;cuts on the Atlantic Coast Line Railroad, between the Junction and Northnbsp;Anna River, a thin remnant may be seen of the usual character, resting onnbsp;the eroded surface of the older Mesozoic (Rhmtic), and capped by Quaternary and Appomattox. On the North Anna River, a short distancenbsp;above its junction with the South Anna, the Potomac sand maj' be seen

sliowing four or five feet under the Eocene. Here, as is commonly the case in Virginia where the Eocene marine strata rest immediately on thenbsp;Potomac sand, a layer of large cobbles is found in the top of the latter.nbsp;The area of Potomac here shown may be called the Hanover area.

Between the South Anna River and Richmond is another gap in the exposures, none being found until Richmond is reached.

Near Ashland, however, on the surface, there is a large quantity of cobblestone, which seems to be the debris from eroded Potomac. A recent well-boring in Ashland disclosed under the Appomattox, and over thenbsp;older Mesozoic, fifty-six feet of material that may belong to the Potomac.nbsp;It is highly probable that the formation underlies this interval, but toonbsp;deeply buried to be reached by the slight excavating power of thenbsp;streams.

At Richmond, owing to the deep erosion of James River, the Potomac is shown again. It is, however, barely exposed away from the immediate bank of the river, being covered by the Tertiary, both Eocene andnbsp;Miocene lying above it. Immediately on the river all the Tertiary hasnbsp;been cut away as fiir down as Deep Bottom, where it makes its firstnbsp;appearance in the river bank. At Richmond, and down the James tonbsp;Deep Bottom, Quaternary alone is found in the river banks above thenbsp;Potomac. The same is true along the Appomattox to near Petersburg,nbsp;where the Appomattox formation, witli the Tertiary underlying it, comesnbsp;above the Potomac. Away from tliese rivers, in the triangular areanbsp;between them and between Richmond and Petersburg, where we maynbsp;expect to find the Potomac, the surface is mostly composed of the Appomattox formation, showing in a few places small patches of Tertiarynbsp;exposed beneath it. This area of Potomac may be called the Petersburgnbsp;area. Its west margin may be taken as approximately determined by thenbsp;Atlantic Coast Line Railroad, which runs between Richmond and Petersburg. Along this margin the Potomac is mostly hidden under its ownnbsp;ruins and the thick covering of Appomattox material. It is to be seennbsp;exposed only along the James and Appomattox Rivers, and from whatnbsp;may be seen on these streams the formation is continuous at least as farnbsp;south as Petersburg, twenty miles from Richmond.

Along; the James from Richmond to Deep Bottom, twenty-one miles by river below that city, the Potomac formation shows itself in the basenbsp;of most of the bluffs and high banks, rising to various heights and cappednbsp;by Quatex�naiy. Considering the variability of the material, it is herenbsp;surprisingly like that found in the Fredericksburg and Baltimore areas.nbsp;On the James its greatest thickness is attained in Drury�s Bluff, eightnbsp;miles below Richmond. Here about sixty feet of it can be seen. Innbsp;Chafin�s Bluff, a little below Drury�s Bluff, for a long distance it showsnbsp;a thickness of ten to twenty feet. In the vicinity of Dutch Gap it isnbsp;exposed for several miles, reaching its maximum thickness in Trent�snbsp;Reach, where forty feet may be seen.

On the Appomattox it may be found at many places up to Petersburg. Its greatest thickness on this stream is foxind at Point of Rocks. This is four miles above City Point, where the James and the Appomattoxnbsp;unite. Here fully eighty feet may be seen. It is noteworthy for thenbsp;coarseness of the sand which makes up most of the formation, and for thenbsp;large size and abundance of the pebbles and cobble-stones found in it.nbsp;Some of the latter, composed of Potsdam quartzite, attain the dimensionsnbsp;of ten or twelve inches. This point, although one of the most easternnbsp;exj)osures, shows the formation in the Petersburg area at its maximumnbsp;of thickness and of coarseness, whicli, as on the Potomac River, indicatesnbsp;that the eastern margin of the formation is still far distant. The easternnbsp;limit of exposures in this area may be fixed by a line drawn from a pointnbsp;on the Appomattox tliree miles above City Point, in a direction a littlenbsp;east of nortli, to Deep Bottom, on the James. Although exposures do notnbsp;occur east of this line, there is good reason to tliink that the formationnbsp;extends far eastward under the Tertiary terrane.

In 1869 an artesian well was sunk at Fortress Monroe to the depth of 907 feet. This well passed through the Miocene and Eocene strata, andnbsp;at the deptli of 835 feet entered a material which differed totally from thenbsp;Tertiary, but possessed the peculiar features of the Potomac formation.nbsp;I he boring was still in this formation when it was stopped, so that at leastnbsp;seventy-two feet of this mav be found liere. Professor Rogers had annbsp;opportunity to study the material from different depths in this well and he

gives a description of itd It is surprising to find here, so far to the east, the heterogeneous composition, coarse character, and indications of thenbsp;action of agitated waters so characteristic of the Potomac formation in itsnbsp;exposures far to the west. Professor Rogers speaks of a conglomerate ofnbsp;clay, sand, and pebbles, which reminds us of the features seen in thenbsp;erosion horizons of the Potomac He mentions coarse sandy clay withnbsp;brownish or reddish blotches, clay and sand with some coarse pebbles,nbsp;reddish mottled clay with quartz pebbles, and other features common innbsp;the Potomac, but found in no other formation under the Eocene of thenbsp;Atlantic slope.

Fortress Monroe, at the mouth of James River, is on an air line in the direction of the declination of the strata, sixty miles distant from the lastnbsp;exposures seen on the James and the Appomattox. Tlie average declination of the surface of the Potomac formation is from these data about fourteen feet to the mile. Tlie strata in this, as in the Fredericksburg area,nbsp;sink in a southeast direction. ^ As no regular dip can be determined, we cannbsp;note only the depression of the surface of the formation taken as a whole.

South of Petersburg no detailed examination has been made in search of Potomac outcrops, and lienee too much stress should not be laidnbsp;on the apparent absence of them in given places. South of this town,nbsp;along the eastern margin of the Azoic rocks, no Potomac has been seennbsp;until the Nottoway River, twenty miles distant, is reached. In this interval the Potomac, if present, is buried under a thick mass of the Appomattox formation, and there is no stream capable of cutting down throughnbsp;it. The country or dirt road from Petersburg to Weldon, in North Carolina, runs near the margin of the crystalline terrane, and hence outcropsnbsp;of Potomac, if they exist, would appear near this road. As stated, nonenbsp;are seen for twenty miles. When we reach the Nottoway the formationnbsp;again appears.

At Bolling�s Bridge, where the road above mentioned crosses this stream, a few feet of typical Potomac sand with clay balls may be seen innbsp;the base of the bank. This is capped by a thin stratum of Eocene withnbsp;obscure impressions of marine shells. This exposure was apparently not

seen by Professor Rogers. About four miles higher up the river there is another outcrop of a few feet of Potomac in the base of the river bank.nbsp;Tliis was seen by Professor Rogers. In both places the material is a coarsenbsp;sand of brownish-gray color, which contains many pebbles, some of whichnbsp;are three inches in diameter. At tlie bridge occur balls of dark gray claynbsp;of a foot or-more in diameter, which, as in the areas farther north, arenbsp;embedded in the pebbly sand. The two exposures considered alone indicate here an area only four miles long; but tlie coarse pebbly character ofnbsp;the sand, taken with the fact that only the top is shown, seems to show thatnbsp;this, which may be called the Nottoway area, is much more extensive.nbsp;The river in cutting down has evidently barely reached the top of the formation.

As the Potomac of the Nottoway area in the most important points possesses exactly the same features as those of the more northern areas,nbsp;there can be little doubt that, if we could trace each of the areas eastward,nbsp;we should find them uniting to form one continuous terrane extending fromnbsp;north of Baltimore to the Nottoway. South of the Nottoway unequivocalnbsp;Potomac has not been seen. In portions of Greenville County some ofnbsp;the Appomattox beds are strikingly like the pebbly sand of the Potomac,nbsp;and indeed seem to be composed of the debris of Potomac strata but littlenbsp;modified. This may explain the announcement of the existence of the formation in this part of Virginia made by Professor Rogers in his earliestnbsp;reports, but not repeated in his later ones.

Until tlie Roanoke at Weldon is reached the streams do not seem to have cut down through the Tertiary, and hence they do not reach thenbsp;horizon of the Potomac. The Roanoke, however, at Weldon, in Northnbsp;Carolina, has cut down to the Azoic rock, but it is difficult to find exposures at the level where the Potomac may be looked for. The river innbsp;flood deposits a large amount of mud on its banks and in the channels ofnbsp;the creeks emptying into it, and this hides everything. Except immediately on the river a thick covering of the Appomattox foi�ination here, asnbsp;everywhere south of the Nottoway, conceals even the Eocene and Miocenenbsp;beds. At Weldon, near the north end of the railroad bridge, a smallnbsp;stream, a mere spring branch, flows at a low level into the Roanoke. Over

a very small space it lias stripped tlie floor of gneiss of the covering which conceals it. In contact with the gneiss a layer a few inches thick is found,nbsp;consisting of coarse sand and gravel, showing some of the characteristicnbsp;features of the Potomac. It looks like a mere remnant of what was anbsp;formation of some extent, but which in this place has been almost entirelynbsp;removed by erosion, and it suggests the idea that the Pot-ornac may benbsp;found as far south as this place. The exposure, however, is too slight to benbsp;taken as anything more than suggestive of probabilities.

If we take the lower Potomac as ending in the vicinity of the Nottoway, and extending east only as far as Fortress Monroe, it will still rank among the more extensive formations of the Atlantic coast region. Stretching from Baltimore to the Nottoway, its length would be about two hundred miles. This, with an average width of sixty miles, would give twelvenbsp;thousand square miles as the approximate space occupied by the Potomac.

There is good reason to think that the present westernmost exposures of the Potomac do not determine the original extension of the formationnbsp;in that direction. It seems at one time to have been present considerablynbsp;farther west than any of the outcrops now visible. The formation atnbsp;various horizons contains deposits of pebbles and cobble-stones. These arenbsp;chiefly composed of quartz, but in some portions rounded stones of variousnbsp;hinds of ciystalline Azoic rocks occur. In the vicinity of Washingtonnbsp;some cobbles and pebbles of Potsdam quartzite may be seen. In thenbsp;Petersburg area, especially along the James and Appomattox Rivers, thenbsp;Potsdam material is noteworthy for its abundance and the large size of thenbsp;stones.

On the weathered surface of the lower Potomac and on that of the formations adjacent to its outcrops a large amount of gravel and cobblestones occurs of the same nature as the material found in the Potomac.nbsp;It would seem that the original home of this surface material was thenbsp;lower Potomac, and that the stones were liberated on the erosion of thatnbsp;formation. Except along the streams which cross from the Potomac intonbsp;the Tertiary terrane, these gravels do not pass far into the region occupiednbsp;by the Tertiary and later formations. On the rivers they are foundnbsp;forming the basal portion of the Quaternary, and as this often rests

directly on the Potomac, it is not always easy to distinguish the Potomac gravels from the later ones. In this material the Potsdam cobbles are thenbsp;most significant, and tliey are usually easily identified. The Potsdamnbsp;gravel is not seen north of Washington, and south of that city it is notnbsp;traced farther than Pohick Church, near White House Point. Thisnbsp;distribution indicates that these stones were brought down the Potomacnbsp;River, which crosses for the last time outcrops of the Potsdam a little westnbsp;of Harper�s Ferry. The Potsdam cobbles may be seen throughout thenbsp;Petersburg area near the outcrops of the Potomac, and they are found,nbsp;as near Washington, over a belt of country extending considerabl}^ tonbsp;the west of it and within the Azoic terrane. They may be followed alsonbsp;all along to the west of the Hanover area, and five or six miles to thenbsp;north of its termination. Much rounded quartz material is found withnbsp;these stones. In the Azoic terrane they are often found inclosed in Appomattox clays and sands.

The distribution of this coarse, loose material indicates that the Potomac once extended west of its present exposures over a belt varyingnbsp;from ten to tvmnty miles in width.

So much has been said in the preceding pages concerning the geology of the formation, that the remarks under this head may be much abbreviated. It is very difficult in any brief general account to give a clearnbsp;idea of the character of this formation. Tlie want of regular structurenbsp;and the continual, often abrupt, changes in mineral character and physicalnbsp;features make it necessary to give a separate description of each locality.nbsp;Sections at the same locality, taken at intervals of a few yards or even feet,nbsp;vary generally in most of their features. It is impossible to take the dipnbsp;and strike, and no single bed can be traced over any large area. Thisnbsp;arises from the fact that the characteristic mode of arrangement of thenbsp;materials is in irregular po�kets, or more commonly in interlockingnbsp;lenticular layers. The layers may each continue throughout, containingnbsp;the same kind of material, dovetailing between layers of a very differentnbsp;kind. A layer, on being traced horizontally or vertically, may pass

gradually or abruptly into something quite different. The individual layers may be variously constituted, and show in their parts on a minornbsp;scale the variable features discerned in the composition and the groupingnbsp;of the layers taken as a whole. Then on various horizons matter previously deposited seems to have been torn up, transported to varyingnbsp;distances, and deposited in a confused manner. These last-named featuresnbsp;mark what, for the sake of distinction, I call erosion horizons. They addnbsp;much to the irregularity of the formation. When one has before him anynbsp;considerable exposure of the lower Potomac he may well hesitate tonbsp;attempt an accurate description of it, feeling that this would require annbsp;examination of each yard of the material.

The layers of sand are often marked by undulating lines across the direction of their length, forming a marked current bedding. This featurenbsp;is conspicuous m the cuts on the narrow-gauge railroad west of Fredericksburg. We may often find gravel, coarse sand, and clay pelletsnbsp;confusedly mixed together. This is to be seen at the top of the quarrynbsp;on Acquia Creek on a large scale. While no regular dip could be madenbsp;out from the tracing of individual strata, the formation as a whole sinksnbsp;gently to the southeast.

Two principal kinds of material make up the lower Potomac beds; namely, sand and clay. The sand is by far the most abundant. It is thenbsp;typical material, while clay occurs in limited local layers, either inclosed innbsp;the sand or replacing portions of it, owing to the graduation of the sandnbsp;into it.

The sand may be loose, or cemented into a pretty firm sandstone, which has been used as a building stone. This is its nature to a considerable extent on Acquia Creek and around Stafford Court House. It isnbsp;more generally friable and incoherent, especially in outcrops. All thenbsp;material near the Potomac River and north of it has this character, butnbsp;the larger portion of the sand of all the areas does not form a coherentnbsp;rock. The indurated sand or sandstone generally forms irregular masses,nbsp;inclosed in the more friable material, or some irregular portion of a friablenbsp;stratum may show this induration. The crumbling sandstone or sand isnbsp;often quite fine in texture, and has more or less of a light-colored to white

clay, which serves as a cementing- matter, in which the grains of sand are embedded. There seems to be some connection between the presence ofnbsp;this clay and the incoherence of the material, but we find loose sand withnbsp;little or none of this clay. This is the material which Professor Rogersnbsp;has called �feldspathic sand.� I have seen no feldspar, fresh or decayed,nbsp;in this material, and the clay, although often quite white and pure, is rarelynbsp;the direct product of the decay of feldspar. This argillaceous sand generally has a white or light gray color.

In some places the amount of the clay thus intimately mixed with the sand makes up a large proportion of the material, forming from one-fourthnbsp;to one-third or more of the bulk. This sort of sand is common aroundnbsp;Fredericksburg, and may also be found in the lower part of the bluff atnbsp;White House, as well as in many other places. Strange to say, we maynbsp;find this dispersed clay mixed with coarse sand and even with pebbles.nbsp;Tins is the case at White House, for example, and at Point of Rocks nearnbsp;City Point. The base of the bluff at White House Point to the height ofnbsp;fifteen or twenty feet is composed of a very coarse white indurated sand,nbsp;containing a large amount of diffused white clay, and in places manynbsp;quartz pebbles. These are half an inch in diameter and under, and theynbsp;are irregularly scattered through the mass of the rock. At Point of Rocks,nbsp;on the Appomattox, seventy feet and more of this material is exposed. Itnbsp;contains pockets and irregular courses of large cobbles, most of them ofnbsp;Potsdam quartzite, some of them attaining the diameter of ten to twelvenbsp;inches. Here we find, in one place at least, several masses of the pale reddish Potomac clay embedded in this coarse mixture. One of these blocksnbsp;was two and one-half feet long and subangular-prismatic in shape. Therenbsp;is a large amount of this irregularly mixed coarse material and white claj^nbsp;in Trent�s Reach. In one layer here the cobbles of Potsdam and othernbsp;material abound, and many of them are eight to ten inches in diameter.

These characters in the sand indicate that it was laid down in agitated and probably shallow waters, in which tliere was little or no sorting of the'nbsp;materials.

ever seen in any of the beds of tlie Fredericksburg area. It is more com-MON XV--4

mon in some of the gray clays of the Petersburg area, but it is not there abundant. This is not what we would expect if we attribute the origin ofnbsp;the material to the crystalline rocks lying to the west of the Potomac. Innbsp;most of these mica forms a large proportion of the rock, as in the granite,nbsp;gneiss, mica-schist, hornblende-schist, etc. The sandy matter of the Potomac is by most persons called a sandstone, but it is more properly a sandnbsp;in most cases. The gradation in the fineness of the material and thenbsp;change in the proportion of clay and sand, as has already been stated, arenbsp;not what we should expect if the sediment came from the west, the materials being coarser and having more sand in the exposures farthest east.

The color of the sand, especially of the lower beds, when they contain much diffused clay, is light gray or white; but this material, owing apparently to the oxidation of diffused pyrite, is sometimes colored yellowish, reddish-brown, etc., the colors being in irregular patches and seams.nbsp;This coloration often follows, and makes much more distinct the planes ofnbsp;current-bedding.

Towards the upper part of the formation there is a considerable admixture of colored and impure clays with the sand, which then tends to assume brownish-gray, yellowish-gray, and other kindred colors. Thenbsp;colors are in such cases often ai-ranged so as to produce a mottling on anbsp;small scale of gray with other colors, or a blotching on a large scale.nbsp;Towards the western margin of the Fredericksburg, area, and especiallynbsp;between Acquia Creek and Occoquan, there is a large proportion of sandynbsp;clays of various colors�gray, reddish, yellowish, etc. The colors here arenbsp;often arranged irregularly, producing mottling and blotching. Thesenbsp;colored impure clays are in considerable force along the route of thenbsp;Atlantic Coast Line Railroad between Alexandria and Telegraph Station.nbsp;Possibly some of the Variegated Clay members may be found with thesenbsp;clays.

Pebbles and cobbles, as will appear from what has already been said, are not uncommon in the lower Potomac. They occur at different horizons within the beds and ai�e common towards the top. Very generally innbsp;Virginia, where the Eocene rests on the Potomac sand, the upper portion ofnbsp;the latter is a layer of cobbles packed in sand. This is the case at Rich-

mond, where a well dug- through the Eocene to the top of the Potomac disclosed a layer of large cobbles, many of them composed of Potsdamnbsp;quartzite, and some ten inches in diameter. The same thing may be seennbsp;at Deep Bottom and near Hanover Junction. Indeed, so common is thisnbsp;feature, that Professor Rogers, in his earliest publications on the geologynbsp;of Virginia, called attention to the trenched and eroded character of thenbsp;lower Potomac surface upon which the Eocene rested, and to the accumulation of large stones in places on this surface.

These stones are to be found also generally where the Quaternary rests on the Potomac, and then they attain their maximum in abundancenbsp;and size, deserving sometimes to be called bowlders, since some of thenbsp;Potsdam stones are two feet in diameter, while the Azoic masses are occasionally much larger.

The stones within the Potomac beds are generally small, being two to three inches and under in diameter, but sometimes they attain the diameter of five to six inches and more. They occur sometimes aggregatednbsp;into irregular beds and pockets, then attaining their largest size. Thenbsp;smaller pebbles are often very abundant, scattered through the generalnbsp;mass of the rock, and showing no particular relation to the inclosing material. This may be sand, coarse or fine, or it may be clay. This showsnbsp;that there was little sorting action in the waters.

As stated before, Potsdam material is not seen in the northern areas except in the vicinity of Washington, for in the areas north of Fredericksburg the inclosed stones are usually quartz or Azoic. In the Petersburg area, as before stated, tliese are accompanied by an abundance ofnbsp;Potsdam cobbles. No Potsdam stones were seen in the Nottoway area.nbsp;The Nottoway River does not cross the Blue Ridge and touch the Potsdam terrane, as do the James and the Potomac. The Potsdam quartzitenbsp;is found in place on the western flanks of the Blue Ridge, but not eastnbsp;of it.

e find these stones in the top of the lower Potomac where the Variegated Clays rest on the sand, but sufficient exposures of this contactnbsp;have not been seen to enable one to say what is generally the case at suchnbsp;S' junction. It is not an uncommon thing to find plant-impressions in the

disturbed clay which is frequently associated with these deposits of stones. The rich plant-layer at Fredericksburg rested on a mass of cobbles. Thenbsp;plants found on the Telegraph road near Potomac Run, and those on thenbsp;railroad near Brooke, as well as the richest deposit of clay at Dutch Gap,nbsp;are all associated with pebbles.

It is worthy of mention that Professor Rogers, noticing the abundance and large size of the Potsdam cobbles at Point of Rocks, and knowingnbsp;that they must have been brought from the Blue Ridge, speaks of them asnbsp;marking a diluvial era of ancient times. At that period many geologists,nbsp;and Professor Rogers among them, were disposed to explain the phenomena of the drift of the glacial period by assuming the existence of anbsp;diluvial rush of waters.

The clays found in the lower Potomac are, as has already been stated, merely subordinate masses occurring occasionally in the sand.nbsp;They are important simply from the fact that they contain all the plant-impressions and nearly all of the undisturbed lignite. Their character and mode of occurrence have already been given. The originalnbsp;isolated pure clay layers are usually thin, being one or two feet thick,nbsp;but they may suddenly swell up to considerable dimensions, as at thenbsp;lower entrance of Trent�s Reach. They may split up and be lost in thenbsp;sand, and they generally disappear by thinning out and dovetailingnbsp;between sand layers.

The sandy mottled clays formed by the graduation horizontally of a sand into clay are more considerable in amount. This material may benbsp;greenish or grayish in color, and when traced horizontally it may assumenbsp;reddish colors in large masses; or, again, the colors may be intermixed sonbsp;as to resemble mottled castile soap. In the vicinity of Fredericksburgnbsp;this kind of material replaces large portions of the normal sands, and itnbsp;sometimes extends over considerable areas, but witliout any regirlarity ofnbsp;occurrence. As illustrating its occurrence, we may take tbe conditionnbsp;of things seen at Cockpit Point Hei�e the lowest exposed material is anbsp;greenish, gray argillaceous sand. If we follow it, we see it in places becoming more nearly a pure clay, but it then soon becomes again sandy,nbsp;and is now marked in huge blotches witli a brilliant red color. In places

the entire mass is red. Still farther on it changes to a light gray sand, which is totally unlike the material in other places. This sort of changenbsp;is common in the Fredericksburg area, but was not seen in the Petersburg district.

A beautifully white, pure, plastic clay is sometimes found in the form of balls, embedded in the sand. It was seen, for example, in the lowernbsp;part of White House Bluff. It has never been seen in the original ornbsp;undisturbed beds.

The layers of isolated plastic clay in their original position sometimes show peculiar features in their arrangement, and illustrate the ii i-egularity of the lower Potomac formation. Sometimes, as at Dutchnbsp;Gap, we may see in the same vertical exposure several of these layers.nbsp;They may be found in the sand inclined at different angles to one another,nbsp;and in one case several were seen diverging from a common point likenbsp;the outspread fingers of a hand. Of course such layers must be depositednbsp;upon a shifting surface. These layers are sometimes cut off at one endnbsp;by coarse sand and gravel. When partially cut away they are frequentlynbsp;associated with clay balls which have been torn from them.

The isolated clay balls and masses often show peculiar features. They occasionally are seen where no trace is left of the bed which furnished tliem. Some clay masses, four or five feet in diameter, embeddednbsp;in coarse sand, may be seen at the plant locality on the railroad nearnbsp;Acquia Creek, the dark gra,y clay contrasting strongly with the lightnbsp;colored sand. In Trent�s Reach, where considerable cliffs of nearly whitenbsp;sand occur, we may see a number of large balls of gray clay embeddednbsp;in the sand, and displayed on the same horizon for a considerable distancenbsp;in the face of the bluff.

The embedding of clay balls in coarse sand is one of the most constant and characteristic features of the lower Potomac. Clay balls thus inclosed may be seen at all exposures of the formation from Baltimorenbsp;to the Nottoway River, and the clay is strikingly similar in all cases.nbsp;Clay balls and irregular deposits of disturbed clay are common in the topnbsp;of the lower Potomac sand, associated with the pebbles and cobbles ofnbsp;that horizon. This clay seems to point to the former existence of an

argillaceous member in the top of the lower Potomac, like that seen at Federal Hill, Baltimore, resting on the sand and apparently extendingnbsp;over a wide area. As this member, from its position, was the portion ofnbsp;the lower Potomac most exposed to erosion, and as it was soft and easilynbsp;destroyed, we might expect to find it preserved less commonly than thenbsp;underlying sand. If the lower Potomac has lost much from erosion, thisnbsp;member, if it existed, would suffer most. There is good reason to thinknbsp;that in the long period of time that has elapsed since the deposition of thenbsp;lower Potomac it has lost much of its thickness. Allusion has alreadynbsp;been made to the trenched and eroded condition of its surface where, asnbsp;in Virginia, it is covered by the Eocene, In Virginia the outcrops of thenbsp;Potomac occur at very different altitudes, so that it may in some placesnbsp;stand much higher than the Eocene and younger formations, even whennbsp;found in the ijnmediate vicinity. An example of this may be seen atnbsp;Point of Rocks, on the Appomattox. Here the Eocene occurs only a milenbsp;away. It is exposed in a ravine much below the level of the surface ofnbsp;the Potomac at that point. The two pre-Eocene ravines near Brookenbsp;have been mentioned. They give another example of a worn surface.nbsp;In Maryland, between Relay and Baltimore, where the Variegated Claynbsp;rests on the lower Potomac, miich irregulaidty is shown in the heightnbsp;of the top of the latter formation. Of course, where the Quaternarynbsp;rests on the lower Potomac the greatest variation is shown in the heightnbsp;of its surface. A striking case is at White House Bluff, where eightynbsp;feet of the formation seen in the point shows on each side Quaternary tonbsp;the level of the water. Many other localities on the Potomac River andnbsp;elsewhere might be mentioned where the lower Potomac rises high abovenbsp;the surrounding Quaternary.

While from this extensive erosion of the lower Potomac we would expect to find the former uppermost portions of it generally missing, wenbsp;find in some places remnants which appear to represent it. These havenbsp;been already mentioned, being the clay bed near the railroad in thenbsp;vicinity of Brooke, the upper argillaceous portion of the lower Potomacnbsp;at Mount Vernon, and the plant-bearing argillaceous material occurringnbsp;in the top of the formation at Federal Hill. This latter may, I think, be

considered typical of this portion of the lower Potomac, and for this reason the section at Baltimore will be given further on. We may, then, withnbsp;some probability conclude that the original uppermost portion of tlie lowernbsp;Potomac in most of the areas was more argillaceous than the typical sandnbsp;now representing most commonly the formation.

I am thus particular in speaking of this possible uppermost member for several reasons. It seems that, if we can assume its existence, it maynbsp;explain tlie difference seen in the facies of the flora found at certain pointsnbsp;It has already been stated that the most noteworthy plants found in thenbsp;embedded bowlders at Deep Bottom, also those in the disturbed clay atnbsp;tlie 72d mile-post near Brooke, and in the bank near the railroad in thenbsp;vicinity of the last locality, are dicotyledons; and that these in manynbsp;cases have a younger aspect than the plants found elsewhere, as at Fredericksburg and at Dutch Gap.

At the same time, in the places first named, the dicotyledons outnumber the ferns, cycads, and conifers, which is not the case at most of the Potomac plant localities. The material at Deep Bottom containing thesenbsp;plants, as well as that at the 72d mile-post, looks as if it were the ruins ofnbsp;this argillaceous upper member. The clay layer in the bank near thenbsp;mile-post, but farther down the railroad, looks like an uneroded remnantnbsp;of such a member, and this is true of the plant-layer at Baltimore. Thisnbsp;latter contains some dicotyledons similar to some of those found nearnbsp;Brooke. It might, then, be supposed that the younger aspect of thenbsp;dicotyledonous plants at these places is due to the fact that they belong tonbsp;a flora distinct from that typical of the lower Potomac, and that thisnbsp;occurs in an independent younger group of beds.

But there are many difficulties in the way of this supposition. The connecting links are too numerous. Too many plants found in the localnbsp;floras having an older facies occur with these. The stratum in Whitenbsp;House Bluff, which contains numerous dicotyledons like those occurringnbsp;near Brooke, is not found so placed that we can admit that it belongs tonbsp;a group of beds distinct from and younger than the normal lower Potomac sand. It has twenty to thirty feet of this coarse sandy matter abovenbsp;it, and it is clearly a member of the typical lower Potomac. In all the

other cases it is impossible to separate the material carrying these dicotyledonous plants from that containing the seemingly older ones. There is no break between the beds, and the general geological features are thenbsp;same in all. An attempt will be made in another connection to give thenbsp;significance of these apparently younger elements, If anj^ more argillaceous upper member was ever generally present in the lower Potomacnbsp;it is synchronous with it, and the two form one unbroken series

A good type of the upper member, whose probable wide extent has been noticed above, may be found in the southeast slope of Federal Hill,nbsp;Baltimore. The spot is located on Covington street, near Ellicott�s ironnbsp;furnace. The exposures seen at the time of my visit (August, 1886) werenbsp;necessarily temporary, as they were made in the grading of a sti�eet andnbsp;in slight excavations formed for the purpose of obtaining sand from thenbsp;sandy member o,f the lower Potomac. Professor Uhler writes that thenbsp;aspect of the place has since been totally changed. The hill has been dugnbsp;away and the pits have been filled up.

I was informed by intelligent persons who had much experience in excavating the Potomac beds at Baltimore, and whose business compellednbsp;them to make a close study of the different kinds of rocks found there,nbsp;that the features seen in the section given belorv might be seen at a number of other points in and near the city. In the descending order wenbsp;have:

The Variegated Clay (No. 4) has already been described in its general character. It descends from the top of the hill to near its base. It is mostly a tenacious gray clay, quite plastic towards the base, and whennbsp;obtained from that horizon it is used for making tiles, etc. It has no bedding and no cleavage, is much contorted and affected with slickensides,nbsp;. contrasting strongly in these points with the clay of No. 3. While graynbsp;is the normal color, it is in places variegated in large blotches with red

and other colors, dne to iron oxide. Irregular masses of it are sometimes sandy. It has often small bits of plants and fragments of lignite, but nonbsp;lignitic entire trunks were seen. The bottom of this clay is easily distinguished from the top of No. 3 by its peculiar structure. At the samenbsp;time the clay of No. 3 is rather more sandy.

No. 3 consists of alternations of gray clay and argillaceous sand, showing a distinctly bedded arrangement, but much irregularity in thenbsp;thickness and other features of the constituent beds. The lower portionnbsp;has a predominance of sandy matter, but the clay increases as we ascend,nbsp;and in the top it exceeds the sand in amount. The sandy layers of No. 3nbsp;are gray in color and more argillaceous than No. 1. They have manynbsp;blotches and streaks of yellowish-brown and reddish colors mingled withnbsp;the dingy gray, which is the principal color, and the layers swell iip andnbsp;thin away in the most irregular manner. At the base of No. 3 and restingnbsp;on No. 2 we find in several places two or three feet of a tender ash-graynbsp;shale, with patches and irregular lenticular thin partings of fine sandynbsp;matter. This is the portion that contains the recognizable plant-impressions. This portion, and indeed all the clay of No. 3, is easily distinguished from the Variegated Clay by most of the workers in the Baltimorenbsp;clays, and the plant-bearing part is called �shelly or slaty clay.�

No. 2 seems to be simply the upper part of No. 1, which has been impregnated with iron. It is not universally present, being generallynbsp;wanting when formations younger than the Variegated Clay rest on No. 1.

No. 1, at Federal Hill, has clay balls with some pebbles, and it is stained reddish in some irregularly shaped portions by iron oxide. It isnbsp;here very friable, appearing as an incoherent sand. It has very littlenbsp;diffused white clay or so-called kaolin. It is sought for on account ofnbsp;the comparatively pure sand that it yields.

The Variegated Clay seems to be a northern formation. As stated before, the point farthest south at which it has been seen with its characteristic features is Fort Washington. Here it is much thinner than betweennbsp;Washington and Baltimore. If it appeal�s in Virginia, it occurs withoutnbsp;the features which are so conspicuous farther north. It has not beennbsp;recognized in that State.

This group of clays appears to he greatly developed northeast of Baltimore, and from the statement of Professor Rogers, previously quoted,nbsp;it extends into Delaware.

Mr. McGee has found in this clay formation at the head of Chesapeake Bay some poorly preserved plant-impressions, which are nearly all dicotyledons. These impressions are too few in number and too imperfectnbsp;to throw any clear light on the question of the age of the formation. Innbsp;the absence of any evidence that shows the Variegated Clay group to benbsp;distinct from and decidedly younger than the lower Potomac formation,nbsp;its close association with the latter and the difficulty of separating thenbsp;two make it necessary to group them together as forming one series ofnbsp;beds.

As the Variegated Clay group furnishes none of the plants described in this memoir, igt;o further description of it is called for.

In what will be said under this head the evidence of the fossil plants will not be used, but the horizon of the lower Potomac will be fixed sonbsp;far as it can be done on evidence independent of them.

Throughout most of the area occupied by tlie lower Potomac the base when seen has been found to be composed of the crystalline rocks,nbsp;whose age must be placed so far back that they give us no aid in determining the lower limit of the horizon of the Potomac. But in the vicinitynbsp;of Hanover Junction this formation may be seen resting on the erodednbsp;surface of the older Mesozoic, with evidence of a decided break betweennbsp;them. This older Mesozoic in this part of Virginia, as I have shown innbsp;Monograph U. S. Geological Survey, No. VI,^ is Rhsetic in age; at leastnbsp;the plant-bearing portion of it. If the strata of this formation overlyingnbsp;the plant-bearing part differ from the rest in age, they are of coursenbsp;younger.

The striking differences generally found in the lithologic and structural features of the two formations indicate that the difference in their ages is considerable, the Potomac being decidedly the younger. Time

enough must have elapsed to permit an almost total change in the geologic conditions under which the two formations were laid down. The inland bodies of water, in whicli the older Mesozoic was for the most partnbsp;deposited, had been drained ofiF, so that deposition in Potomac times tooknbsp;place only outside of the crystalline terrane, within which nearly all of thenbsp;older Mesozoic is to be found. The older Mesozoic areas and the crystalline rocks adjoining them are cut by numerous trap dikes. Not a trace ofnbsp;these traps can be found in the Potomac beds. The period of igneousnbsp;activity which has left so many traces, probably at the end of the Oldernbsp;Mesozoic time, must have then been over when the Potomac sedimentsnbsp;were accumulating. These facts do not enable us to fix the lower limit ofnbsp;the Potomac horizon very definitely, but at least we can say that the formation is considerably younger than the Rhmtic.

The upper limit in age can be fixed more nearly. The marine Cretaceous of New Jersey and Maryland is wanting in Virginia, as is the Variegated Clay formation. In this State the oldest formation which restsnbsp;upon tlie Potomac, and whose age is fixed, is the Eocene. Well-exposednbsp;contacts of the Eocene with the older formation may be seen in a numbernbsp;of places. The greensand marl bed is the oldest portion of the Eocene thatnbsp;contains any considerable number of fossils. This bed contains, amongnbsp;others, such shells as Ostrea, Turritella, Pecten, Ciftherea, CucuUea. This bednbsp;in all of the area south of Fredericksljurg, and at this place also, restsnbsp;directly upon the typical sand of the lower Potomac. This latter, in allnbsp;such cases, gives evidence of having lost much from erosion, and its uppermost portion nearly always contains large cobbles. Towards the northernnbsp;part of the State we find under the greensand bed, it is true, a variablenbsp;thickness, amounting in some cases to from seventy to ninety feet, of non-fossiliferous sand)^ matter. This, however, from the glauconite that it contains and other features, belongs to the Eocene formation. Under it thenbsp;lower Potomac still shows marks of great erosion.

The Eocene is a true marine formation, laid down under very different conditions from those attending the deposition of the lower Potomac. Thenbsp;eastern margin of the continent must have become depressed enough tonbsp;permit the sea to occupy portions that in lower Potomac times showed

only shallow agitated waters, and .an abundant marine fauna flourished where hitherto no trace of marine organisms has been found.

Judging, then, from the condition of things in Virginia, we must conclude that the Potomac is considerably older than the oldest Tertiary. In the District of Columbia and in Maryland we have the Variegated Claysnbsp;superposed on the lower Potomac. At Relay Station, where the clays restnbsp;on the lower Potomac sands, these last show the same marks of erosion andnbsp;the same pebble-bed as in Virginia, where the marine Eocene occupies anbsp;similar place. At Federal Hill, where we find the Variegated Clays resting on an argillaceous member interposed between them and the sands,nbsp;the indications of a lost interval are not so decided, but still they may benbsp;seen. We may then conclude with some degree of assurance that thesenbsp;Variegated Clays are younger than the lower Potomac, although not yetnbsp;clearly separable^ as a distinct formation. So far as the evidence goes, itnbsp;indicates that the Variegated Clays probably are of the same age as thenbsp;plant-bearing Soiith Amboy clays of New Jersey. These have been heldnbsp;to be nearly of the age of the Cenomanian of Europe. If this is correct,nbsp;then from the stratigraphy and general geologic features the lower Potomac beds must be regarded as considerably younger than the Rhaetic andnbsp;somewhat older than the Cenomanian. There is, at least in the evidencenbsp;above given, nothing wliich opposes the assumption that the age of thesenbsp;beds is Neocomian.

It is proper, in this connection to say something as to the origin of the lower Potomac beds, or the conditions under which they were laid down;nbsp;because, as it happens, they appear to be similar to those attending thenbsp;accumulation of a formation which in Europe has a number of plantsnbsp;closel}^ allied to those of the lower Potomac. In order that the readernbsp;may appreciate the peculiarly irregular character of �this formation, it maynbsp;be well to repeat in a summary the leading features that may be seen in it.nbsp;If the exposure of the beds at any locality is considerable, all of thesenbsp;features might be seen there.

The lower Potomac is usually a mass of sandy matter of varying coarseness, generally incoherent, and liaving some light-colored interstitialnbsp;clay. It has usually a light gray to white color, but this is very often

marked irregularly with colors due to oxide of iron. No regular bedding or structure is found, but we have a series of interlocking lenticular layers,nbsp;showing extreme variableness in composition, texture, and structure. Tlienbsp;arrangement shows mostly current-bedding, and not uncommonly beach-structure. Dispersed pebbles and clay balls, also nests and pockets ofnbsp;pebbles and cobbles and disturbed clay, are frequent. Lenticular sheets,nbsp;occasionally partially cut away and sometimes containing plant-remains,nbsp;are often�met with. These are intercalated in the sand in the most irregular manner, and occur at no fixed horizon, lying sometimes inclined tonbsp;one another, as if deposited on a shifting surface.

These features mark the lower Potomac at all its exposures from the Nottoway River to Baltimore, and, so far as they can be shown in borings,nbsp;they appear to be present as far east as Fortress Monroe. Such characters could be pi'oduced only in deposits accumulating in unquiet andnbsp;comparatively shallow shore waters, or in the estuary of a great river.

The entire absence of all marine life shows that the waters must have been fresh, or at most brackish.

That the deposits accumulated near land, and probably in part at least in estuary waters, is strongly indicated by the nature and distribution of the plant-remains. The great quantity of dispersed lignite in thenbsp;form of isolated logs and limbs seems to show that the amount of driftnbsp;timber must have been large. These trees were probably floated down innbsp;the larger streams.

The areas showing thickly placed logs of lignite, appearing to be formed out of trees which fell where they grew, seem to point to portionsnbsp;of the shore or to islands in the estuary which were suddenly submerged.nbsp;The delicate ferns and other plants, often preserved in great perfection,nbsp;could not have been drifted far or floated long in the agitated waters without being destroyed. They probably grew on islands.

It seems probable that the James and Potomac Rivers had their representatives in lower Potomac times in two streams, which in theirnbsp;course may not have differed essentially from the present rivers.

If we are permitted to assume that at the time of the accumulation of the lower Potomac sediment two such rivers existed, and, further, that

they were much larger than their representatives and united to form a great estuary whose waters extended at least from Petersburg to Baltimore, we could explain the origin of many of the features of the formationnbsp;now in question.

The character and distribution of these beds seem to indicate that the margin of the continent covered by these estuary waters was subjected tonbsp;oscillations of level, so that the shore-line retreated and advanced. If wenbsp;assume that this margin was first rapidly depressed and then elevatednbsp;without pause, unquiet conditions would prevail throughout the epoch, andnbsp;marine life could not be established in the area affected.

The tendency of the action of the waves and river currents would be to work over deposits recently made and to produce the peculiar effectsnbsp;due to alternating erosion and sedimentation wliich are so conspicuous innbsp;the lower Potomac beds. The tendency would also be to work thenbsp;deposited matter seawards and to give in that quarter thicker accumulations than those found on the western margin, for this would be submergednbsp;only temporarily.

If these assumptions be correct, there would be a noteworthy similarity in the conditions attending the formation of the lower Potomac strata and those of the Wealden of Europe, and it is interesting to notenbsp;tliar in the plant remains of the lower Potomac there is an important element which finds its nearest relations in that formation.

DESCRIPTION OF THE SPECIES.

None of the Equiseteoe except Equisetum have been found in the flora of the lower Potomac. Neither of the species of Schizoneura, which occurnbsp;in the flora of the older Mesozoic, or RhaBtic of the Richmond Coal Field,nbsp;appears. As compared with the species of Equisetum of the older Mesozoic. thpse of the Potomac formation show a marked change. In the oldernbsp;Mesozoic the variety of forms, it is true, is small, but the number of individuals of Equisetum Bogersi is very great, and the specimens are often tonbsp;be found filling certain strata in such numbers as to show that the plantsnbsp;must have grown thickly over large areas, and must have formed thenbsp;greater part of the vegetation of the marsh. The great size attained by allnbsp;of these individuals and the rarity of their branching show that theynbsp;belong to tlie Triassic and older Jurassic type.

The species of the Potomac strata show decidedly more modern aspects, and clearly belong in type to the younger Jurassic and Wealden,nbsp;showing marked affinity with the species of these periods, especially thenbsp;latter. Specimens are rare, and they occur singly, scattered very sparinglynbsp;in certain strata. Tlie plants were small and mostly much branched. Innbsp;these points they resemble living forms.

Stems and branches branch copiously; the diameter I�anges from 3�� to 8��, the average being I�quot;*; length of internodes, 8�� to 22��; sheaths

closely appressed, 5�� to lO�� long; teeth visible on the upper surface of stems and branches, 5 to 6. They are usually linear, lanceolate, acute,nbsp;rarely somewhat obtuse, and approximate.

This pretty little Eqiiisetmt has not been found anywhere except at the single locality given above. At this place it is rare. This species innbsp;general appearance much more nearly approaches living forms than E.nbsp;Boffersi, which is its last predecessor in this region. It is very close tonbsp;E. Burcliardti Schimper, from the Wealden of Germany, and perhapsnbsp;should be identified with that species. It does not, however, show thenbsp;swollen sheaths and the wide divergence of the teeth seen in tlie Wealdennbsp;species. Still, something of both of these features may sometimes be seen.

The most noteworthy features of the Potomac species are the copious branching and tlgt;e slight diminution in the size of the successively formednbsp;branches. In many cases there is little or no difference in the size of thenbsp;stem and the branch which it sends off. The mode of branching seemsnbsp;to be quite often dichotomous, but this may possibly be the effect ofnbsp;compression. The specimens are often partially or wholly decorticatednbsp;so as to show no teetli, and in most of the specimens the teeth appear,nbsp;from maceration, to be narrower and farther apart than they werenbsp;originally.

The unusual forms shown in PI. II, Figs. 1-3, appear to be portions of the main stem, or at least of the primary branches They show sixnbsp;teeth, while the smaller and much more common forms show five. Thenbsp;eidarged portion, PL I, Fig. 1'^, gives what seems to be the normal originalnbsp;form of the teeth. They are closely approximate, and have a short acutenbsp;tip. PL I, Fig. P, shows a slightly different form of teeth. They arenbsp;blunter and farther apart at the tips. This is perhaps due to distortionnbsp;from pressure and partial maceration.

Tliis plant must have attained a considerable height. It has much resemblance to the genus Casmrina in the mode of branching, its copiousness, the great length of the branches, and their woody character.

Schenk^ says of Lyelli, from the Wealden of England: �It has a branching stem, with internodes �2� long, and is 10�quot;� to 13quot;quot;� in diameter.nbsp;The branches are 5quot;quot;� in diameter. The sheaths are 1�'� long, and the teethnbsp;are linear and acuminate.�

The Potomac plant in most of these features agrees closely with JE. Lyelli. The form given in PL II, Fig. 4, and the smaller stem in Fig. 5 ofnbsp;the same plate, are probably brandies. The resemblance is especiallynbsp;close in the long, narrow, and remotely placed teeth. This plant has alsonbsp;a marked likeness to E. iMsikmicum Heer, from the Jurassic of Portugal.^

Localities: The form given in PI. I, Fig. 7, comes from Fredericksburg, and the others from the fishing hut above Dutch Gap Canal.

Plate II, Fig. 8, depicts a fossil which appears to be the rhizome of an equisetum. It shows no sheaths, is jointed at unequal intervals, and hasnbsp;on the upper surface three or four narrow prominent ridges. It seems tonbsp;be decorticated, and is probably the rhizome of E. Lyelli.

Stems branching copiously; branches long and slender; surface smooth; branches 1.5'�'� and less in diameter; internodes 15�� or a littlenbsp;more in length; sheaths slightly swollen, 2'��* long; teeth visible on thenbsp;branches, three to four in number, very short, oval in shape, and terminating in short acute tips.

Specimens of this little Eijuisetwn may be found occasionally in the shale, especially of Covington street. They are mostly in the form of

^Compare Heer�s Coiitrib. FI. Fos.s. Portugal, Lisbonne, 1881, PI. VIII,� Figs. 1-6.

slender decorticated branches, often attached to stems but slightly larger than the branches, in such a manner as to indicate that the branching wasnbsp;copious; in this respect reminding one of JS. Virginic,um. The branchesnbsp;average in diameter 1�� and under. Considering their slenderness, theynbsp;have a remarkably rigid and woody aspect. The length that many ofnbsp;these impressions attain and their stiff character remind one of Gasuarim.

PL CLXX, Fig. 8, gives a specimen found at Covington street, Baltimore. It seems to be the decorticated rhizome of some Equisetum, showing two tubercles. Only one specimen was found. As E. Marylandicim occurs at this spot, it is probable that this rhizome belongs to it.

The ferns form a very important element in the Potomac flora. Notwithstanding the great variety of forms, with very few exceptions specimens of ferns are rare at all the localities. This comparative scarcity of individual preserved fossils is no doubt due to the conditions attending thenbsp;fossilization, which favored the preservation of other plants in larger proportion. The large number of species, although represented by comparatively few individuals, shows that ferns abounded. There is a curiousnbsp;mingling of older and more recent aspects in the fern-flora. Taken as anbsp;whole, Jurassic and Wealden types decidedly predominate. The verynbsp;large proportion of species belonging to the Qladophlebis and Thyrsopterisnbsp;forms gives a marked Jurassic facies to the flora. Many forms are closelynbsp;allied to Sqdiempteris Mantelli aud other Wealden species, so that the Weal-den element is a large one. But the numerous species of Aspidkm givenbsp;modern features a strong representation.

In the ferns, as in most of the other plants of the Potomac, we And much isolation of the species, forms occurring at a given locality beingnbsp;commonly restricted to it. In some of the species of CladopJdebis we findnbsp;some of the closest approximations made by Potomac forms to those of thenbsp;older Mesozoic or Rhsetic flora of the Richmond Coal Felds. This latter

flora is in the Potomac terrane, the one which came next to the Potomac flora among its predecessors.

Saporta^ first defined the character of the genus Cladophlehis. He gives the following description: �Frond pinnately divided; pinnules separate from one another, or slightly united, attached to the rachis by thenbsp;entire base.� Schimper^ gives a much fuller analysis of the generic character. He says: �Eironds pinnately divided; pinna? spreading; lobes ornbsp;pinnules attached by the entire base, sometimes confluent, rarely slightlynbsp;auriculate, acuminate, or obtuse, occasionally dentate, especially at thenbsp;apex, not rarely subfalcately curved upwards; midnerves pretty strong;nbsp;secondary nerves departing at a more or less acute angle, dichotomousnbsp;a little above the base, and repeatedly dichotomous: slender to verynbsp;slender.�

In his later work, however, for Zittel�s Handbuch der Paleontologie, he makes no mention of this genus. If we modify Schimper�s description so as to make it read, midnerve strong at base, and towards the summit dissolving into branches, we have a very accurate description of anbsp;group of ferns that is strongly characteristic of the Jurassic, and which isnbsp;fully as much entitled to be called a genus as is Sphenopteris or Pecop-teris. In my opinion it is necessary to retain the name Cladophlebis fornbsp;all fossil plants with the above-described character, and which have nonbsp;fructification by which they can be placed in other genera. It does notnbsp;seem proper, as some have done, to group under this specific name allnbsp;the Jurassic plants of the Cladophlebis type, which have more or lessnbsp;resemblance to the Pecopteris Whitbiensis of Bindley and Hutton and thenbsp;different plant given the same name by Brongniart. Pecopteris Whitbiensis, used by Heer as a specific name for plants widely diffused over thenbsp;world in the Jurassic period, is nearly equivalent to the generic namenbsp;Cladophlebis. Again, because certain Jurassic plants of the Cladophlebisnbsp;type have in their foliage some of the features of ferns possessing the fructification of Asplenium, Dichsonia, etc., it does not seem proper to group

1 Pal. F I'rauc., 2d series, V�g�taux, PI. Jurass., vol. 1, pp. 2^8, 299. �Trait� de Pal. V�g., vol. 3, p. 503.

them as Asplenium, Dicksonia, etc., when they have no fructification and are found in countries far remote from the supposed fructified forms. Fornbsp;the reasons given above, the generic name Gladoplilebis is retained for Mesozoic fossil ferns which possess the character given by Schimper, amendednbsp;as suggested.

Plate II, Fig. 11; Plate III, Fig. 2; Plate VI, Pigs. 5, 6,8-14; Plate XXI, Pigs. 9,13; Plate CLXIX, Fig. 2.

Frond bipinnate or tripinnate, arborescent; principal rachis slender; primary pinnte remotely placed, very rapidly becoming shorter in ascending; ultimate pinnae very remotely placed, alternate, in the lower part ofnbsp;the frond pinnately lobed; in ascending on the frond abruptly passingnbsp;first into pinnules with undulate margins and then into those with entirenbsp;margins; pinnules mostly very remotely placed, thick and leathery, alternate, at their tips subacute or obtusely rounded, often constricted at base;nbsp;in shape oblong to ovate; the midnerves of the pinnules towards theirnbsp;summits split up into branches. The lower lateral nerves are once ornbsp;twice forked, the upper ones once forked.

Localities: Fredericksburg; 72d mile-post, near Brooke: Deep Bottom; Covington street, Baltimore. In all these places rare.

I have united in this species a number of forms which differ somewhat in facies, but not enough to form the basis of specific separation. In PI. XXI, Figs. 9, 13, are given two small fragments coming from Deepnbsp;Bottom, being the only specimens found there. They are thick andnbsp;leathery in character, and differ considerably from the fine specimennbsp;given in PI. II, Fig. 11, which comes from Fredericksburg. The smallnbsp;fragment depicted in PI. CLXIX, Pig. 2, comes from Covington street,nbsp;Baltimore. Tliis also is leathery in character, and is much smaller thannbsp;most of the normal forms. The forms given in PI. VI, Figs. 3, 12-14, comenbsp;from the 72d mile-post, near Brooke. Their texture is very leathery andnbsp;thick, and the general character of the pinnules is not exactly that of thenbsp;type form, which may be considered as given in PI. II, Fig. 11. PI. VI,nbsp;Fig. 9, gives a small fragment from Fredericksburg which in facies isnbsp;much like a Gleichenia, and is quite aberrant.

The smaller forms of this species are somewliat like Pecopteris borealis Brong., which, as Heer has shown, occurs in Koine, Greenland. Pecopterisnbsp;Uherata Heer in the JuraSsic flora of Cape Boheman,^ has the pinnulesnbsp;constricted at base, and is a good deal like some of those found in thisnbsp;species. But neither one of these species is near enough to the Potomacnbsp;plant to be identifled without hesitation with it.

The leaf substance of all the specimens of this plant must have been thick and leathery, for the pinnules and lobes make deep impressions innbsp;the shale, and some of the rounded small pinnules and lobes leave roundnbsp;pits. The epidermis of the pinnules seems to have been thick and durable,nbsp;for the specimens often have a dark brown shining surface. I have, withnbsp;a good deal of hesitation, placed in this species some of the specimensnbsp;given in the figures named

Among described fossils, Schenk�s AletJiopteris cycadina stands nearest to the plant now in question. The resemblance is considerable betweennbsp;the form given in PI. VI, Fig. 2, and Schenk�s Foss. Flor. d. nordwest-deutsch. Wealdenformation, PI. X, Fig. 2.

Frond bipinnate or tripinnate; principal rachis slender, with a keel in the middle; pinnae quite remotely placed; pinnules broad, very obtuse,nbsp;with undulate margins; alternate, subauriculate, and rounded off at base,nbsp;attaclied by tlie middle of the base, separate and rather remote; midnerve,nbsp;as in the genus generally, strong at base, and towards the summit splittingnbsp;up into veins; lower lateral nerves forming copiously branched groups;nbsp;tliose higlier are bifurcate, and simply forked, slender, but very distinctlynbsp;defined; leaf-substance thin.

flliis beautiful species was found only at Fredericksburg, and but two specimens were obtained.

The dimensions and character shown indicate that the plant was probably arborescent. It is nearly allied to no fossil known to me. It is more

like Pecopteris Ilaihurnensis, L. and H., from tlie Oolitic formation of Hai-burn Wyke, Yorkshire, England, than any other previously described plant, but is quite distinct from tliis. It has some resemblance to Neurop-teris imclulata, L. and II., Foss. Flor., vol. 2, PI. LXXXIII.

Frond bipinnate or tripinnate, arborescent; principal rachis very stout and woody ; rachises of the penultimate and ultimate pinnte stout,nbsp;rigid, on the under side rounded and prominent, on the upper side ridgednbsp;on each margin; ultimate pinnm very long, rather remote, subopposite;nbsp;pinnules alternate to subopposite, at the tips varying from acute to obtuse,nbsp;with margins usually very entire, rarely crenulate to subdentate, in shapenbsp;ovate to lanceolate and subfalcate, attached by the greatly widened base,nbsp;mostly separate to the base; midnerve stout at base, but soon becomingnbsp;attenuated, and some distance below the summit splitting up into veins;nbsp;lateral nerves at the base of the pinnules branched several times, in somenbsp;cases forming nerve-bundles, in ascending towards the tips of the pinnulesnbsp;less and less subdivided, finally simply furcate and unbranched.

d�his splendid plant is perhaps the most common fern at Fredericksburg, but it is not abundant there. The specimens are usually quite fragmentary, as if they had been transported some distance. From the size of the rachis shown in PI. Ill, Fig. 3, the plant must have been arborescent. The rachis of the pinnm in all the specimens is strong and rigid.nbsp;The under side of the rachis is usually rounded and prominent. On itsnbsp;upper surface a strong ridge is often seen on each margin, and to this thenbsp;pinnae and pinnules are attached. The pinnules of PI. Ill, Fig. 3, may benbsp;taken as typical for form and dimensions. Sometimes, however, pinnulesnbsp;may be seen which are quite obtuse at their tips, and in some cases theynbsp;occur with margins showing incipient lobing. These come probably fromnbsp;lower portions of the frond. Possibly in PI. IV, Figs. 1, 3, may be denoted a smaller species of this type.

This plant is plainly Jurassic in type, and may be regarded as a survivor of the Jurassic flora. It is so much like the sterile forms of the plant from the older Mesozoic or Rlimtic flora of Vii'ginia, first made known bynbsp;Bunbury and described by me in Contributions to the Knowledge of thenbsp;Older Mesozoic Flora of Virginia,^ under the name Acrostichides linncB-cefoliiis, that one is tempted to consider it as a descendant of the latter.nbsp;Comparison maybe made with PL VII, Fig. 1, and PI. VIII, Fig. 1, ofnbsp;the work cited. It is also in some points much like Acrostichides rhombi-folius, described in the same monograph.

The Potomac plant is strikingly like Brongniart�s Pecopteris Whit-biensis, and F. tenuis, and one may well hesitate to separate them. Heer, in Flor. Foss. Arctica, vol. 4, under the name Asplenitim, has describednbsp;some forms that are very close to the plant now in question. It does not,nbsp;however, seem proper to make the Potomac plant an Asplenium so long asnbsp;it shows no fructification.

Frond bipinnate or tripinnate; rachis of the pinnte rather slender; pinnules opposite to alternate, attached by the entire base, oblong to lanceolate, subfalcate, minutely dentate toward their tips, those in the uppernbsp;part of the frond entire; midnerve as in the genus; lateral nerves bifurcate or simply forked, and rather slender.

I have with much hesitation united the plant given in PI. IV, Fig. 2, which comes from Fredericksburg, and that depicted in PI. VII, Fig.nbsp;7, which was found on the road-side near Potomac Run. The latter differs from the former in having the pinnules more erect, oblong in shape,nbsp;and separate to the base. Then, too, they have their nerves simply forked,nbsp;and more Pecopteris-like. The very fragmentary nature of the specimensnbsp;does not permit the true nature of the species to be fully made out.

The form given in PI. VII, Fig. 7, may be compared with Pecopteris denticulata, Ileer, as given in Flor. Foss. Arctica, vol. 3, Die Kreideflora

des Arctisclien Zone, PI. XXVI, Fig. 7. The Potomac plant resembles this a good deal. The form from Fredericksburg given in PI. IV, Fig.nbsp;2, is much like Nenropteris ligata,^ L. and H., but the nerves are morenbsp;copiously branched and the pinnules are broader. The Potomac plant isnbsp;no doubt nearer this latter than any other described form.

Frond bipinnate or tripinnate, arborescent; rachis of the primary pinnee or of the frond stout and rigid ; pinme opposite, with a moderatelynbsp;strong rigid rachis; pinnules mostly opposite, sometimes alternate, falcate,nbsp;acute to obtuse, separate to the base, and slightly rounded off on the uppernbsp;side, witli margins mostly entire, rarely slightly lobed, attached by thenbsp;whole of the broad base, varying in size according to position on the frond.nbsp;The pinnm of ultimate order, in ascending on the frond, pass through pinnules that are long and falcate with slightly lobed margins, into those ofnbsp;smaller size with entire margins; midnerve rigid and continued to nearnbsp;the summit, with comparatively little diminution in size. The lateralnbsp;nerves are bifurcate and go off at an acute angle, and curve outwards tonbsp;meet the margin.

ddiis fine plant is one of tlie most common ferns at Fredericksburg. It has, more than is usual in the Cladophlebids, the aspect of an Aletliop-teris, and although a good deal larger, is something like the Fecopteris Wliit-biensis of Lindley and Hutton. The Jurassic ferns that have some resemblance to this species are numerous, and it is hardly worth while to refernbsp;to all of them, as none of them can with much probability be identifiednbsp;with it. The forms with larger pinnules may be compared with Fecopterisnbsp;insignis, L. and H but, besides other points of difference, the nervation isnbsp;essentially distinct.

Ileer�s Asplenimn specMhile^ Flor. Foss. Arctica, Jura. Flor. Ost. Sib., vol. 4, PL XXI, Figs. 1, 2, has the nervation of this plant. The Potomacnbsp;specimens, with smaller pinnules, resemble more or less a number of

Jurassic ferns from widely separated portions of the globe. Among these we have Neuropteris recentior, L. and H., Foss. Flor. of Great Britain, PLnbsp;LXVIII, and several of the fossils united by Heer with Asplenium Whiibi-ensis, in his article on the Jura. Flor. Ost. Sib., Flor. Foss. Arctica, vol. 4,nbsp;No. 2, p. 94, Pecoptcris Indica of Oldham and Morris, and Nathorst�s figuresnbsp;of Gladophlehis nehbensis from the Rhsetic of Sweden, resemble in somenbsp;points the smaller forms of the Potomac plant. Some of the pinnules ofnbsp;C. nehbensis show a fine toothing similar to that found on Gladophlehisnbsp;denticulala.

I have with some hesitation grouped under the species C. falcata several forms that do not resemble in all respects the moi�e common and typical specimens of that species, which may be taken as represented in PL V, Figs. 1, 2. The bluntly terminated pinnules in PL V, Figs. 3, 5, also thenbsp;very slightly falcate pinnules and the nerves of PL VII, Fig. 2, show anbsp;departure from the normal form.

Frond bipinnate or tripinnate; principal rachis proportionally very stout and rigid; pinnae short, alternate to subopposite; pinnules alternate,nbsp;ovate, subfalcate, acute, except in the upper part of the frond, separate tonbsp;the base; midnerve as in the genus; lateral nerves mostly once forked;nbsp;leaf-substance thick. '

In the shape of its pinnules it belongs to the same type as G. Virgini-ensis, but the nerves are not so copiously branched towards the base of the pinnules, and do not diminisli in the number of branches so rapidly towardsnbsp;the summit of the pinnules. It is much like Gladopldebis pseudowhit-biensis,^ but is a smaller plant. It resembles also the upper part of Pecop-teris dentata, given by Lindley and Hutton in Foss. Flor. of Great Britain,nbsp;PL CLXIX. The nerves, however, do not agree with those of that plant.

This small fern is probably another survivor of the Jurassic, or rather Rhsetic, flora of Virginia.

�Contributions to the Knowledge of the Older Mesozoic Flora of Virginia: U. S. Geol. Survey, Mon. No. 6, 1883, p. 52, PI. XX.VII, Fig. 4.

Plate V, Pig. 7; Plate VII, Fig. 6; Plate X, Figs. G, 7 ; Plate XI, Figs. 7,8; Plate CLXVI, Fig. 5.

Frond bipinnate or tripinnate, arborescent; principal rachis stout and rigid; pinna3 witli stout rigid rachises go off at an angle of 45� and curvenbsp;upwards; pinnules alternate, united at base, falcate, ovate to oblong,nbsp;acuminate; midnerve rather stout and rigid, prolonged to near the summitnbsp;of the pinnules; lateral nerves furcate, with branches subparallel.

Localities: Hill-side near Potomac Run, I�ather common; rare -at fishing hut above Dutch Gap Canal.

This plant has some of the features of the Pecopteris type combined with those of Cladophlebis. The pinnules show sometimes an inclinationnbsp;forward along the rachis. In tlie typical forms, such as PI. XI, Fig. 8, thenbsp;pinnules are united at base and decidedly falcate. PI. XI, Fig. 7, andnbsp;PI. V, Fig. 7, give forms with unusually long and slender pinnules. Tlieynbsp;probably represent ultimate pinnae changed in the upper part of the frondnbsp;to pinnules. PI. X, Fig. 6, differs from the normal forms a good deal, andnbsp;hesitatingly I unite it with the species now in question.

Cladophlebis acuta is more like Dunker�s Neuropteris Alhertsii from the Wealden of Germany than any other previously described fossil, and is nonbsp;doubt quite near the Wealden species. Sciienk, in Foss. Flor. nordwest-deutsch. Wealdenformation, PI. VI, Fig. 4, gives a form with the namenbsp;Alethopteris Albertsii, which resembles our plant more than do the figuresnbsp;of Dunker. Heer, in Flor. Foss. Arctica, vol. 6, Pt. 2, Pis. XVI, XXVIII,nbsp;XLVI, has given a number of figures of a plant which he identifies withnbsp;Dunker�s species, but which he calls Fteris Albertsii, making it a Fterisnbsp;without any evidence from fructification. The Potomac fossil is very closenbsp;in form to the figure he gives from Unter Atanekerdluk, PI. XVI, Fig. 6.

Frond bipinnate or tripinnate; arborescent; ultimate pinna; long and linear, with rigid and comparatively stout rachises; pinnules alternate,nbsp;oblong, very slightly falcate, in the upper part of the frond with entire

margins, in the lower portions of the plant with crenate margins; midnerve pecopteris-like, rigid, and prolonged to near the summit of the pinnules; lateral nerves very regularly once forked, with branches subparallel; leaf-substance thick and leathery.

Localities: Fredericksbui�g, very rare; more common but still rare at fishing hut above Dutch Gap Canal; found also in the banks of Dutchnbsp;Gap Canal, and in the red clay ball occurring in these banks.

This plant is rare at all the localities where it occurs. It is found in fragments that are too small to give a good idea of the character of thenbsp;frond. That represented in Fig. 5 was found in the red clay ball whichnbsp;occurs in the right-hand bank of Dutch Gap Canal; To judge from thenbsp;size of the rachis in Fig. 5 the plant must have attained very considerablenbsp;dimensions. This specimen shows a ridge on each side of the rachis.nbsp;This is one of the forms that possess some of the features of Pecopterisnbsp;and Alethopteris. It does not bear much resemblance to any previouslynbsp;described fossil known to me. It seems to be nearest to Pecopfcns WJiit-hicnsis of Lindley and Hutton. It appeal�s also to be like Cladoplilehisnbsp;Virginiensis of this work, but can not be united with it by transitionalnbsp;forms.

Plate IX, Figs. 7-9; Plate X, Figs. 1, 2; Pl.ate XIII, Figs. 1-3; Plate XIX, Fig. 1; Plate XX, Fig. 6.

Frond bipinnate or tripinnate; rachis of the primary and secondary pinna; strong and rigid; pinnm mostly alternate, rarely opposite, going offnbsp;at an angle of 45�, and closely placed; pinnules alternate, obliquelynbsp;rounded at base above, and slightly decurrent on the lower side; in shapenbsp;ovate-acuminate and falcate; margins with distinct crenate toothing;nbsp;midnerve as in genus; lateral nerves of the basal lobes of the pinnulesnbsp;fasciculate and pahnately diverging, those of the upper lobes once ornbsp;twice forked.

Localities: Fredericksburg, most common; 72d mile-post, near Brooke; hill-side near Potomac Eun; rare.

The crenate lobing of the pinnules seems to be a constant feature, and there does not appear to be any tendency to pass into entire pinnules.

Most of the specimens figured come from Fredericksburg. PI. IX, Fig. 2, a form with opposite pinnm, comes fi�om the 72d mile-post, nearnbsp;Brooke. PI. XIII, Fig. 3, comes from the hill-side near Potomac Run.nbsp;It has the lobes more rounded than usual. The pinnules are often decurrent some distance on the rachis.

This plant is not very near any described fossil known to me. It may be compared with Gyatliea Tcliihatchewi, Schmalhausen,^ but showsnbsp;obvious differences. In the shape of the pinnules the species is nearest tonbsp;Pecopteris borealis, Brong., as figured by Heer,^ from the Kome beds, butnbsp;this latter has the nerves single.

Nature of frond and pinnae unknown; pinnules alternate, oblong, acute, slightly falcate, attached by a widened base under a large angle;nbsp;midnerve vanishing before attaining the tip of the pinnule; lateral nervesnbsp;not seen; leaf-substance thick.

Localities: Fredericksburg; hill-side near Potomac Run; at both places very rare.

Frond bipinnate or tripinnate, arborescent (?); pinnae of ultimate order, opposite, short; pinnules, ovate-lanceolate, acute, inclined forward, alternate, attached by the whole of the widened base, separate to the base,nbsp;slightly falcate; midnerve of pinnules slender above the base, but continued to near the apex of the pinnules; lateral n�rves once forked.

This plant is a good deal like some of the forms of G. acuta, as given in PI. X, Fig. 6, but the pinnules are smaller and not united at the base,nbsp;and none of the lateral nerves are more than once forked. It is so muchnbsp;like Pteris AlbertsiP Heer, found in the flora of the Atanc beds, that it is

* Beitr. .Jura Flora Rnsslaud�s, PI. HI, Fig. 3. St. Petersburgli, 1879 *Flor. Foss. Arc., vol. 6, Pt. 2, PI. II, Figs. 9�, 10.

with much hesitation that I separate them. Heer thinks that this plant is Uunker�s Neuropteris Albertsii, hut it seems to be quite dififerent from thenbsp;forms figured by either Dunker or Schenk.

Frond bipinnate or tripinnate; principal rachis stout and rigid; pinnae alternate, linear elongate, with rigid strong rachises; pinnules oblong ornbsp;ovate, very obtuse, distant; leaf-substance thick and leathery, slightly falcate, alternate, attached by the entire base ; midnerve pecopteris-like ; lateral nerves once forked and strong.

Locality: Not very rare in the banks of Dutch Gap Canal; rare at fishing hut above the canal.

This small fern seems to be quite restricted in its distribution. It is well characterized by its pinnules, which are small in size, of leatherynbsp;texture, and remotely placed.

Frond and pinnee unknown; pinnules subopposite, ovate to ovate-oblong, obtuse, united at the widened base, going off nearly at a right angle; midnerve as in the genus; lateral nerves once forked, or with onenbsp;branch of the basal pair forking again.

Localities: Hill-side near Potomac Run; bank near Brooke; very rare at both places.

This plant is too rare and found in fragments too small to permit its character to be made out. It seems, however, to be quite distinct fromnbsp;any other fern described coming from the Potomac formation.

Frond tripinnatifid, arborescent; principal rachis stout and rigid; pinnae alternate, curving upwards, with strong rigid rachises; pinnulesnbsp;with thick leaf-substance, opposite or subopposite, in shape linear-lance-

olate, acute, and falcate, narrowed at the base and decurrent, forming a strong wing on the rachis, margins cut more or less deeply into ovate-acute teeth; -midnerve slender, prolonged to near the summit of the pinnules; lateral nerves fasciculate in each tooth or lobe, forming nerve-bundles, with mostly four branches.

This fine, well characterized plant is very rare, and, so far as known, occurs only at Fredericksburg. It seems to have been a fern of largenbsp;size, and wms probably arborescent. Some of the Potomac ferns elsewhere described, such as CladopldeMs crenata and Aspidium Fredericks-hurgense, look a good deal like this plant, but the decided narrowing of thenbsp;pinnules on both sides at the base and the distinct wing in Gladoplihhisnbsp;alata serve to distinguish it.

Geyler gives^a figure^ of his Pecopteris exiliformis, which in general form looks something like the Potomac species, but the differences arenbsp;marked.

Frond and pinnm unknowm; pinnules linear-lanceolate, acute, with margins cut into ovate-acute lobes and teeth; midnerve as in the genus;nbsp;lateral nerves in each lobe or tooth having a midnerve, which sends off onnbsp;each side alternately branches that are mostly single, and curve upwardsnbsp;towards the summit of the tooth.

This plant is too fragmentary to make out its character. It may be merely a portion of the upper part of the frond of some of the speciesnbsp;described under another name. The so-called pinnules look like pinnmnbsp;reduced to pinnules.

Frond bipinnate or tripinnate, arborescent (?); principal rachis stout, rounded, and prominent; pinnge short, with a strong rigid rachis; ultimate

* Foss. Pflanzeu Juraformation Japaus, Palaioutograpliica, vol. 24, 1877, PI. XXX, Fig, 1�.

pinnae, from the lower part of the frond, with alternate, short, broadly ovate, very obtuse, ronnd-lobed pinnules, those of the upper part of thenbsp;frond having the lowest pinnules distinct and more or less round-lobed,nbsp;and towards the summit with pinnules passing through such forms asnbsp;rotundate, subrhombic, and decurrent to entire and rounded, the latter liav¹nbsp;ing the tips round-lobed and very obtuse; nerves varying according to thenbsp;position and shape of the pinnules, those of the round-lobed pinnules andnbsp;of the pinnae reduced to pinnules flabellately diverging in each lobe, thenbsp;branches being either forked or simple. The nerves of the subrhombicnbsp;pinnules have a midnerve, which sends off alternately on each side forkednbsp;or simple brandies. All the nerves are very strongly marked and stout.nbsp;The leaf-substance is thick and leathery.

This plant is well characterized by its very strong prominent nerves and by the varying pinnules, which show some of the features of Splienop-teris, of Thjrsopteris, and of CladopUeUs, respectively. It seems to benbsp;unique.

Frond bipinnatifid or tripiiinatifid; pinnules or uppermost pinnse ovate-lanceolate, obtuse, narrowed much at base and attached by the narrowly winged base of the rachis or midnerve, lower ones deeply andnbsp;obliquely cut into oblong lobes, which are very obtuse and rounded atnbsp;their tips, upper ones cut less deeply and into fewer lobes, at the summitnbsp;united and forming a termination similar to the lower pinnules or pinme;nbsp;nerves flabellately diverging in each lobe, branching several times, verynbsp;fine and closely placed, but very distinct.

This plant, although found in small fragments only and very rarely, is still evidently a distinct species. It should, perhaps, be placed rather innbsp;the Sphenopteris than in the Cladophlebis group of ferns. It is somethingnbsp;like Thyrsopteris pirisca,^ Eichw., as figured by Heer, but the nerves are

Flor. Foss. Arctioa, vol. 4, No. 2, Beitriige zur Flor. Ost. Sib., PI. XVIII, Fig. 8.

more numerously divided and much finer, and the pinnules are longer and proportionately more slender in the Potomac plant.

Frond hipinnate or tripinnate; rachis of primary pinnge comparatively stout and rigid; pinnules, or reduced ultimate pinme, alternate, oblong,nbsp;acute, somewhat falcate, narrowed to the base into a winged petiole, cutnbsp;into ovate subacute teeth; lateral nerves in each tooth composed of anbsp;slender midnerve, which sends out alternately on each side simple nerves.

This plant is in form a good deal like Thinnfeldia variabilis, from the 72d mile-post, near Brooke. The nerves, however, are fewer, coarser,nbsp;and more remote.' It seems to be a distinct new species.

Frond bipinnate or tripinnate; primary rachis slender; pinnules or reduced pinnse petiolate, lanceolate-acute, alternate; leaf-substance thick;nbsp;basal lobe on the upper side of the pinnules or pinnai ovate-obtuse, erect,nbsp;and much larger than the other lobes or teeth; the other lobes or teeth ofnbsp;the pinnules ovate-acute, and directed towards the tip of the pinnules;nbsp;pinnules towards the summit of the primary pinnae sparingly and acutelynbsp;toothed; nerves of the lobes and teeth not seen.

This small plant seems to show the upper portion of a primary pinna in which the ultimate pinnai are reduced to lobes and teeth. It seems tonbsp;be a distinct species.

Ultimate pinnse linear, with a comparatively stout rachis; pinnules subopposite, with a dense leathery leaf-substance, ovate-falcate, acute,nbsp;remotely placed, separate to the base, free on the upper side, and cut

away to form a sort of petiole, attached only b}'' the lower portion of the base; midnerves strong; lateral nerves not seen.

This seems to be a very distinct species. It belongs to the Jurassic type of CladopUehis. It is something like Pecopteris WilUamsoni, Brong.,nbsp;but is a much smaller form.

Pinnules subfalcate, thick and leathery, separate to the base, attached by the whole of the widened base; in shape ovate-acute; nerves not seen.

Tlie small specimen figured was the only one found. It seems to be a distinct species.

Frond, ? ultimate pinnae very short, subopposite, cut to varying depths into rounded, oval, or elliptical pinnules and lobes; pinnules rounded atnbsp;base; nerves strong, rather distant, composed of a midnerve dissolved anbsp;short distance above its base into branches, which are once or twice forked,nbsp;and curve strongly outwards to meet the margin of the pinnules andnbsp;lobes; leaf-substance thick.

This plant is something like Cladophlebis constricta; the nerves, however, curve outward more strongly, and are more copiously branched, and the ultimate pinnm are much shorter. It is also something like Dunker�snbsp;Pecopteris MurcMsoni, but the pinnules are rounded and narrowed at base,nbsp;and the nerves are more flabellate and spreading.

Fronds once or several times pinnate; pinnules mostly entire, attached by the whole of the base, which is rarely narrowed; midnervesnbsp;extending to the tips of the pinnules; lateral nerves going off on each sidenbsp;MON XV-6

of the midnerve in a pinnate manner, and at a varying angle, simple, or several times forked, not anastomosing.

The genus Pecopteris, based mainly on the nervation and probably containing many species of distinct ferns, serves simply as a convenientnbsp;grouping of plants having a particular facies, and whose generic characternbsp;can not be otherwise fixed. There are a number of forms in the Potomacnbsp;flora which have the character given above for Pecopteris, and which isnbsp;taken from Schimper�s description of the genus. The number of ferns,nbsp;however, found in the Potomac flora which could be placed in the genusnbsp;Pecopteris is far less than that of those which possess the characters ofnbsp;CladopUebis and Thyrsopteris. This type is rather feebly represented in thenbsp;Potomac flora.

Plate VIII, Figs. 1-7; Plate IX, Figs. 1-6; Plate XXIV, Fig. 2; Plate CLXIX, Fig. 3.

Frond bipinnate or tripinnate, arborescent; pinnae alternate, very long; leaf-substance thick and durable; the principal rachis and that ofnbsp;the ultimate pinnae stout, rigid, with the margins on the upper face raised innbsp;the form of a cord; pinnules elongate-oblong to narrowly linear, oppositenbsp;to alternate, much narrowed at the base and separate to the base, cutnbsp;away obliquely on the upper side and decurrent slightly on the lower one,nbsp;or else united at base to form a wing along the rachis of the pinnae; margins denticulate to distinctly dentate, straight or more commonly slightlynbsp;falcate; midnerve prolonged to near the tips of the pinnules, often rathernbsp;slender but distinct; lateral nerves once forked, one of the branchesnbsp;usually ending in the tip of the tooth on the margin.

Localities: Red clay ball in the banks of Dutch Gap Canal; fishing hut above Dutch Gaip Canal; Fredericksburg; road-side near Potomacnbsp;Run ; 72d mile-post, near Brooke; near Telegraph Station; Covingtonnbsp;street, Baltimore.

This is perhaps the most widely diffused of the Potomac plants. At the locality on the road-side near Potomac Run the fragments are amongnbsp;the most common. They occur in such a way in the irregularly depositednbsp;clay as to suggest that the dimensions attained by this fern were great.nbsp;The clay was of such a nature at this locality as to render it impossible

to take out the specimens without reducing their size very considerably. In PI. VIII, Fig. 2, is shown a fragment of what was formerly a portionnbsp;of tlie frond a foot wide and more than a foot long. At all the otliernbsp;localities it is rare. It is a singular fact that not a trace of this plant isnbsp;found at the locality on the hill-side, which is not more than one hundrednbsp;and fifty yards distant from that on the road-side. This is true, althoughnbsp;ferns are the most common fossils at the first-named place.

This fern is so well characterized, that there is no difficulty in identifying it. Indeed it can usually be detected at a glance. The plant shows some variation. Some of the pinnules, especially in those specimens foundnbsp;at the fishing hut above Dutch Gap Canal and at Baltimore, are verynbsp;narrow, elongate, and slightly toothed. We may take PI. VIII, Fig. 6, asnbsp;a typical specimen, the teeth being acute; but in Fig. 1 of the same platenbsp;we have a jfiant from Fredericksburg which has the teeth less deeply cutnbsp;and more obtuse. This form somewhat resembles Cladopldebis oblonga.

In most cases, and in typical forms, the pinnules are narrowed at base, strongly decurrent, and united to form a wing, as in PI. VIII, Fig. 4,nbsp;from Fredericksburg, and Figs. 2, 6 ,7 of the same plate, coming from thenbsp;road-side near Potomac Run. In such forms, however, as PL VIII, Fig. 3;nbsp;PI. IX, Fig. 1, from Fredericksburg, and Fig. 5 of the same plate, fromnbsp;the 72d mile-post, as well as PL IX, Fig. 2, from the fishing hut abovenbsp;Dutch Gap Canal, the pinnules are separate, not decurrent at base, lessnbsp;linear, and narrow in form, and less inclined forward. These points maynbsp;be due to the fact that the parts which show them come from a portion ofnbsp;the frond different from that affording the normal forms, or they may benbsp;of sufficient importance to denote a variety of the species.

The form, PL VIII, Fig. 5, from the locality at the 72d mile-post, is the only specimen which gives the summit of a compound pinna. Thenbsp;corded margins of the rachis appear only on the upper surface, as innbsp;PL VIII, Fig. 2, while the lower face is rounded and prominent, as innbsp;Figs. 1, 4, 6 of the same plate. The lateral nerves are typically oncenbsp;forked only, as in PL VIII, Figs. 2�, 2^, but in PL VIII, Fig. 3, and PLnbsp;IX, Fig. 1, the}^ in the lower teeth form nerve-groups, composed of lateralnbsp;nerves which go off alternately from a midnerve.

This plant is more like Pecopteris denticulata,^ Brong., than any other. The only difference is found in the more slender and elongated pinnulesnbsp;of the Potomac 'fossil and in their greater thinness. Pteris frigida,^ Heer,nbsp;from the Atan� beds, resembles the Potomac plant, but it lacks the distinctnbsp;toothing found in the latter.

Plate XIII, Figs. 6-8; Plate XIX, Fig. 9; Plate XX, Fig. 3; Plate XXII, Pig. 13; Plate CLXX, Figs. 5,6.

Frond bipinnatifid or tripinnatifid; rachises slender; pinnae subopposite to alternate, linear; pinnules united for a considerable distance above their bases, oblong, usually obtuse and inclined forward, slightly falcate,nbsp;those of the lower part of the frond denticulate, of the upper part entire;nbsp;leaf-substance thick and obscuring the nerves, which are slender and immersed in it; latertil nerves of the lower pinnules furcate, with the lowernbsp;branch ending in the teeth; lateral nerves of the upper pinnules mostlynbsp;forked only in the basal ones, most of them simple, all usually parallelnbsp;and straight, or nearly so.

This elegant little plant occurs more abundantly at Fredericksburg than at Baltimore. All the specimens figured, except PI. CLXX, Figs. 5,nbsp;6, come from the former place. Still it is not an abundant plant evennbsp;there. PL XIII, Fig. 6, seems to be an abnormal form, which has thenbsp;pinnules united higher up than usual and the lateral nerves more commonlynbsp;forked and more curving than is usual in the pinnules of this fern, whichnbsp;have entire margins. Perhaps it would be better to separate this as anbsp;variety with the name var. unita. PI. XIII, Fig. 7, gives a normal formnbsp;for the pinnse and pinnules coming from the middle part of the frond.nbsp;Fig. 8 of the same plate seems to come from down lower on the frond,nbsp;where the toothing is more distinct and the nervation is all forked. PI.nbsp;XIX, Fig. 9, is a normal form for the parts belonging to the upper portionnbsp;of the frond.

This plant is very much like Pecopteris Browniana, Hunker, of the Wealden of Germany, as figured by Schenk in Foss. Flor. Nordw. Weald-

iHist. V�g.,Pl. XGVIII, Figs. 1, 3. *Flor. Foss. Arc., vol. 6, PI. X, Figs. 1-4; PI. XI, etc.

enformation, Plate V, Fig. 2. The Potomac plant is, however, a stronger form, and the nerves are more commonly single, straight, and parallel thannbsp;in the Wealden fern.

Frond bipinnate or tripinnate, arborescent; pinnules or reduced pinnae subopposite, linear acute, separate to the narrowed base, slightly decurrent, margins cut distinctly into ovate-subacute teeth; midnerve continuednbsp;to the summit of the pinnules or pinnae; lateral nerves furcate.

Localities: Fredericksburg; entrance to Trent�s Reach; fishing hut above Dutch Gap Canal; rare at all localities.

This plant is more common at the Dutch Gap localities than at Fredericksburg, but is nowhere abundant. This fossil is found in fragments too small, and occurs too rarely to permit its true character to be madenbsp;out. It is not close to any previously described fossil known to me.

Frond bipinnate or tripinnate, arborescent?; principal rachis strong and woody; pinnae of the ultimate order opposite, with a rigid rachis; pinnules lanceolate-acute, somewhat falcate, slightly narrowed and decurrentnbsp;at base, attached by the lower portion of the base; distinct, with marginsnbsp;cut into small ovate-acute teeth; midnerve strong at base, lateral nervesnbsp;in each tooth simply forked, or in the lowest teeth with the upper branchnbsp;again forked.

Localities: Fredericksburg; entrance to Trent�s Reach; near Dutch Gap Canal; at each place rare.

The specimen from the Dutch Gap locality, PI. XX, Fig. 11, has a somewhat different facies from the Fredericksburg form, PI. XIX, Fig. 8,nbsp;the pinnules being longer and proportionally narrower. The specimensnbsp;found indicate that the plant was large and probably arborescent.

Frond bipinnate or tripinnate, arborescent !; rachis of the primary pin-nse or of the frond stout and rigid; pinnm alternate, with comparatively stout and straight rachises; pinnules with a thick and durable leaf-substance, opposite to alternate, narrowed at the base, and attached by thenbsp;central portions, those of the lower part of the frond cut deeply into ovatenbsp;acute lobes that are directed slightly forward, subfalcate, those of the middle portion of the frond oblong, acute, subfalcate, with ovate acute teetii,nbsp;the basal lower one being inserted in the angle between the main and secondary rachises; midnerve distinct but slender, extending to the summit ofnbsp;the pinnules; upper pinnae narrowly linear, with ovate subfalcate pinnules united more or less at base; lateral nerves in each lobe or toothnbsp;composed of a midnerve, which sends off alternately on each side branches,nbsp;the lowest one of which on each side is forked ; the others are simple.nbsp;All the lateral nerves are very strong and prominent.

This liandsome fern is very much like Dunker�s Pecopteris Browniana, and it is even more like Pecopteris strictinervis, it being so close to thenbsp;latter that I have hesitated to separate them. The specimen shown innbsp;Fig. 4 seems to be a portion of a compound pinna which comes from thenbsp;upper part of a frond where the pinnae liave become greatly reduced, andnbsp;the large pinnules shown in Fig. 1, coming from the lower portion of thenbsp;frond, and in Fig. 2 from the middle part, are reduced to small ovate pinnules united at the base, and to ovate teeth. The lateral nerves in thenbsp;pinnules and lobes of this specimen are so distinct, that they look likenbsp;threads on the surface of the plant.

Frond bipinnate or tripinnate, arborescent ?; principal rachis stout and rigid ; pinnules, or pinnae reduced to pinnules, subopposite to alternate,nbsp;oblong, acute to obtuse at the tips, short, very uniform in length, cut into

ovate or rounded oblong teeth which are subacute to very obtuse; nerves in each lobe or tooth composed of a midnerve which sends off on eachnbsp;side alternately branches which are single and arch upwards towards thenbsp;the summits of the lobes.nbsp;nbsp;nbsp;nbsp;^

Localities: Hill-side near Potomac Run ; fishing hut, above Dutch Grap Canal; rare at both localities.

As this plant is found only rarely and in fragments, it is possible that it may be identical with some other of the species described from the Potomac formation.

Leaf-substance thick and leathery; principal rachis strong; pinnules, or pinnge reduced to pinnules, subopposite to alternate, narrowed at thenbsp;base, and cut more or less deeply into ovate-acute to obtuse teeth; midnerve of the pinnules, or reduced pinnae, distinct; no lateral nerves in thenbsp;lobes and teeth visible, only a midnerve.

This plant is found rarely and in small fragments. Fig. 7 gives the largest specimen found. The detached ultimate pinnae given in this figurenbsp;agree quite well with the form given by Heer.^ The only diffei�ence is thenbsp;fact that in Heers plant the pinnules, or reduced pinnae, are opposite.nbsp;This may well be the case with the Potomac plant, for the specimensnbsp;found belong to the uppermost and variable portions of the frond, whichnbsp;often differ from the normal forms.

Frond and primary pinnae unknown; pinnules, or reduced pinnae, narrowly linear acute, cut obliquely into oblong or ovate-obtuse lobes ornbsp;pinnules; the pinnules or lobes containing each a midnerve, sending off onnbsp;each side alternately straight, simple branches.

The true character of this plant can not be made out until more and better specimens are found. It has some resemblance to Pecopteris ovato-dentata, and may possibly be the same with that fern.

Alethopteris Broivniana, Schenk, Foss. Flor. Nordw. Weald., PI. XXVI, Figs. 3-5.

Frond tripinnate, arborescent; the rachises of different orders are comparatively stout and rigid; ultimate pinnse short, subopposite or opposite, linear, acute; pinnules varying considerably in different parts of thenbsp;frond, usually quite small, in shape oblong-obtuse to subacute; separate atnbsp;base in the lower� portions of the frond, united slightly in the upper portions, generally separate; in the upper part of the frond the pinnae reducednbsp;to pinnules, either toothed or with entire margins, the former much narrowed at base, forming a sort of petiole.

Localities: Fredericksburg; Baltimore, among the plants collected by Meek, and at Covington street; red clay ball in the banks of Dutch Gapnbsp;Canal; liill-side near Potomac River; 72d mile-post, near Brooke.

This elegant little plant is one of the most widely diffused ferns of the Potomac formation. It is at the same time quite well preserved in thenbsp;specimens found, hence the different parts can be made out pretty well.nbsp;It being thus fully represented, some of the specimens differ somevvhatnbsp;from the European forms of the Wealden. The drawing, PI. XXII, Fig.nbsp;11, is from a specimen collected by Mr. Meek. The nerves of this species,nbsp;although not strong, are very distinct.

Frond bipinnate or tripinnate; rachis in pinnge of all orders, comparatively stout and rigid; ultimate piiinse in the lower part of the frond linear, in the upper part oblong-lanceolate; all alternate; pinnules verynbsp;small, oblong, very obtuse, subopposite, slightly falcate, united at base to

form a wing, with margins undulate or crenate; leaf-substance very thick and leathery; nerves composed in each pinnule of a midrib, which extendsnbsp;to the tip, and sends off alternately on each side into the teeth simplenbsp;branches, all sharply defined.

This little fern, although found only in small fragments, seems to be very well characterized. It has some of the features of a Tliyrsopteris, andnbsp;perhaps should be placed in that genus rather than in Pecopteris. It is notnbsp;closely allied to any described plant known to me.

PTerbaceous plants, with fronds ranging from pinnate to tripinnatifid; pinnules cuneate or lobed, lobes dentate or subdivided ; primary nervenbsp;slender, towards the summit often bifid or dissolved into branches ; secondary nerves diverging towards their extremities, or prolonged into the lobesnbsp;or teeth.

This genus is another of the heterogeneous groups which serve to collect together ferns which may belong to quite distinct genera and species, but which have in common certain features not dependent upon the fructification, and are not otherwise characterized. Tlie number of ferns of thenbsp;Sphenopteris type found in the Potomac flora is small. I place provisionally in this genus a small number of forms. There are a number of plantsnbsp;in the Potomac flora, especially those of the t3�pe of Sphenopteris Mantellinbsp;Brongn., which have predominantly the character of Tliyrsopteris. These Inbsp;have placed under this latter genus.

Frond unknown; rachis of the principal pinnm Avinged, ultimate pin-nse opposite or alternate, short, and terminating in incised and lobed segments with acute tips, broadly winged; pinnules narrowed at the base, incised into oblong acutely dentate lobes, or cut into oblong acute teeth;nbsp;leaf-substance thin; nerves few and distinct; nerves in each pinnule com-

posed of a midnerve, which sends off very obliquely alternate forked or simple nerves that go into the lobes and teeth. In each segment therenbsp;are several nerves, which diverge flabellately into the teeth.

This small plant has a well-marked Sphenopterls facies. It is something like Sphenopterls Williamsonis Brongn. and also resembles somewhat S. denticiilata Brongn., of the Oolite of England, but seems to be distinctnbsp;from both of these and a well marked new species.

Frond tripinnatifid ; secondary pinme opposite, very short, terminating in a round-lobed segment which is cuneate at base; ultimate pinme or pinnules subopposite, the lower ones cut obliquely in broadly ellipticalnbsp;lobes or pinnules nearly down to tlie midrib, lobes and jhnnules narrowednbsp;towards their bases, the upper ones reduced to pinnules which are firstnbsp;lobed and then simple ; pinnules and lobes at their summits rounded, verynbsp;obtuse, and furnished with very minute teeth; nerves of the rounded lowernbsp;pinnules and of the lobes, several times forked and diverging flabellately,nbsp;the ultimate branches ending in the teeth.

Localities: Fishing hut above Dutch Gap Canal; Baltimore, on Covington street; very rare at both localities.

The specimens figured come from the Dutch Gap locality. The plant is more common here than at Baltimore,nbsp;found at the latter place.

Frond tripinnate, arborescent; principal rachis very stout; leaf-substance thick and �coriaceous ; primary pinme opposite, and having a stout, rigid rachis, which is often somewhat flexuous; ultimate pinnae remotelynbsp;placed, very short, passing towards the summit of the principal pinna ornbsp;of the frond through lobed pinnules into entire ones; pinnules remotely

placed, cuneate at base, tliose in the lower part of the frond cut more or less deeply into oblong acute to obtuse lobes, passing towards the tips ofnbsp;the ultimate pinnae into lobed pinnules like those of the upper part of thenbsp;frond, and at the tips into ovate or oblong lobes and teeth. In the uppernbsp;part of the frond they are elliptical, three lobed, or entire; all the pinnulesnbsp;and segments are broad. The ultimate pinnae and the pinnules of thenbsp;lower part of the frond usually terminate in three lobed segments or innbsp;broad elliptical pinnules. The nerves are copiously branched, divergenbsp;flabellately into the lobes and teeth, and are very distinct and strong

Localities: Fishing hut above Dutch Grap Canal, rather common; Fredericksburg; Deep Bottom; near Telegraph Station ; at all except thenbsp;first rare.

This is the most common fern at the fishing hut above Dutch Gap Canal, and a number of good specimens were found there, although nonenbsp;of them are of large size. PI. XXXV, Fig. 4, is somewhat different fromnbsp;the normal forms in showing a keeled principal rachis, and in the narrowernbsp;segments of the pinnules. It resembles PI XXXVII, Fig. 1, the onlynbsp;specimen found at Deep Bottom. In PI. XXXVI, Figs. 5-8, are given thenbsp;normal forms which are most common at the fishing hut locality. Nonenbsp;of the specimens show apparently anything more than fragments of a compound pinna, which, in the case of tlie stoutest forms, may b� a primarynbsp;pinna. The rachises of the compound penultimate pinnm are sometimesnbsp;swollen at the insertion of the ultimate pinnte. The plant is a very wellnbsp;characterized one, and can usually be distinguished at a glance. It is onenbsp;of the more widely diffused ferns of the Potomac flora. It is not nearlynbsp;allied to any previously described plant known to me.

Frond bipinnate or tripinnate; primary pinnae in outline ovate-lanceolate, acuminate; secondary pinnae alternate, approximate, erect, fasti-giate; pinnules alternate and opposite, straight, linear, or linear-cuneate, at base adnate and decurrent, at the apex acuminate, very entire, thenbsp;lower ones often dentate or pinnatifid.

This is Heer�s^ description. To this he adds that the upper pinnules have only a midnerve, while the lower ones have from one to three secondary nerves, which detach themselves at a very acute angle.

The species S. Mantelli seems to he quite polymorphous, and different authorities on fossil plants have united with this species a large number ofnbsp;plants which vary considerably and come from widely separated regions.nbsp;There is quite a lai�ge number of closely allied plants in the Potomacnbsp;flora which have more or less of the characters of S. Mantelli. These maynbsp;be noted as belonging to the type of this species, but it does not seemnbsp;advisable to combine them under one species. Most of them have thenbsp;characters of Thi/rsopteris, and I have described them as belonging to thatnbsp;genus. It is a fact worthy of mention that there are in the Potomac floranbsp;several types which resemble described fossils, and under winch a numbernbsp;of allied species Miay be grouped. Thus we find the type of Sphempterisnbsp;Mantelli, of Neuropteris Alhertsii Dunkr., of Fecopteris Browniana, of Cla-doplilebis (Fecopteris) Whithiensis, etc.

In using the name Sphenopteris Mantelli, I have restricted its application to the forms given on PI. L, Figs. 1, 2, which have clearly the character of the original species. These specimens come from Baltimore, and are found among the specimens collected by Meek at that place. Thesenbsp;specimens do not have their locality fixed exactly, but it appears probablenbsp;that they were obtained from Federal Hill nearer on Covington street.nbsp;The fragments supposed to be S. Mantelli have the principal rachis comparatively very stout, with alternate pinnules, which are cut into narrownbsp;linear incurved lobes and teeth, each having a simple slender nerve.nbsp;Among Meek�s specimens there is one form given in Fig. 2, which isnbsp;smaller than the normal one represented in Fig. 1. In this smaller formnbsp;the principal pinnae are opposite, and the lobes of the pinnules much morenbsp;minute than in the fossil depicted in Fig 1. Probably this plant, with thenbsp;more slender pinnules and lobes, simply represents a different part of thenbsp;frond from that given in Fig. 1, and hence the difference in dimensions.nbsp;The plant is evidently rare at Baltimore, at least on the horizon of the bedsnbsp;yielding the specimens found on Belt and Covington streets, for no spec-

imens liave been found at these localities. It is probable that Meek�s specimens come from a higher level, as the horizon of the Belt and Covington streets plants is not often exposed, and is shown only in excavations madenbsp;near the level of these streets.

Frond unknown; pinnae small, short, alternate, terminated with a denticulate segment like the uppermost lobes or pinnules; pinnulesnbsp;minute, lower ones spatulate and triple-toothed, upper ones spatulate andnbsp;obscurely toothed; leaf-substance thick and leathery, nerves not seen.

The plant is so rare and fragmentary, that its full character can not be made out. It seems to be a new species, characterized by its thick leaf-substance and very minute size.

Frond unknown; rachis of the penultimate pinnae very thick in proportion to the other dimensions, apparently succulent; ultimate pinnae or pinnules very short; pinnules or lobes broadly elliptical in outline, cutnbsp;obliquely into oblong minutely dentate lobes; leaf-substance thick andnbsp;leathery ; nerves not seen.

Although this plant is very rare and fragmentary, it differs from all others known to me in the very thick main rachis and the very small segments into which the pinnules are cut.

The genus Aspidium seems to be largely represented in the Potomac flora. The number of species is considerable, and the large number ofnbsp;individuals belonging to each species seems to indicate that ferns of thisnbsp;group were among the most common ones. The plants are quite commonlynbsp;fructified, the fructification being often very well preserved. The large

development of this genus introduces a strong modern element into the flora, and it is a noteworthy feature that so many well-characterized speciesnbsp;of this genus occur with numerous forms belonging in type to the Jurassicnbsp;flora.nbsp;nbsp;nbsp;nbsp;gt;

The tribe of the Aspidiese is represented in the Potomac flora by forms that belong to the generic types of both Aspiduim proper andnbsp;Dklymochlcena. As with these imperfect specimens the identification cannbsp;not be certainly made with the one genus or the other, it seems best tonbsp;place them all provisionally under the principal genus Aspidkm. Itnbsp;should be noted, however, that some of these species may belong not tonbsp;the tribe of AspidiecB, but to that of the Davalliece.

Plate XI, Pigs. 1-6; Plate XII, Figs. 1-6 ; Plate XVI, Fig. 9; Plate XIX, Figs. 6, 7.

Frond bipinnate or tripinnate, arborescent; rachis of the penultimate pinme very stout and rigid; pinnse of tlie ultimate order mostly alternate,nbsp;rarely opposite or subopposite, with rigid and proportionally rather slender rachises, very long, linear ; pinnules alternate, oblong or ovate, obtuse,nbsp;slightly falcate, and usually somewhat rounded and narrowed at thenbsp;attachment to the rachis, separate, those of the lower pinme with crenatenbsp;margins, those of the upper ones entire, passing in tlie middle part ofnbsp;the frond tlirough pinnules with undulate margins; leaf-substance thicknbsp;and leathery; midnerve similar to that of CladojMebis, that is, strong atnbsp;base and dissolving into branches at the summit; lateral nerves of the crenate and undulate pinnules in groups in each tooth, composed of a midnerve which sends off alternate simple branches, or else of forked nervesnbsp;with one of the branches forking again ; those of the pinnules withnbsp;entire margins usually once forked, all quite distinct; sori very large, reni-form in shape, and distributed in two rows, one on each side of the midnerve, attached to the summit of the upper branch of a furcate nerve.

This plant is one of the most common ferns at Fredericksburg. All the specimens figured come from this place, except that in PI. XI, Fig. 1,nbsp;W'hich comes from near Telegraph Station, where the plant is not rare.

lts relative abundance at Fredericksburg may be due to the fitness of the plant for preservation, since it has a leathery durable leaf-substance. Tonbsp;judge from the specimen given in PI. XII, Fig. 1, the plant must havenbsp;attained a very large size, for this specimen is probably merely a compound pinna not of primary rank. Fig. 3 of the same plate probablynbsp;represents a similar part of the frond, but down lower, where the pinnulesnbsp;show incipient toothing. Fig. 5 of this plate shows pinnules wider thannbsp;usual, with slightly undulate margins. Fig. 6, same plate, probably comesnbsp;from the uppermost part of the frond, where the ultimate pinna? arenbsp;reduced to lobed pinnules.

The ultimate pinna? of the lower part of the frond, as shown in PI. XL, Fig. 3, must have been very long. Fig. 6 of the same plate may 'possiblynbsp;belong to a different species, but more probably represents a somewhatnbsp;abnormal form coming from high up on the frond. PI. XIX, Fig. 7, givesnbsp;opposite ultimate pinnge, a rare occurrence. The sori in this fern arenbsp;proportionally veiy large.

The plant has no close affinity with any described fossil known to me. It is nearer Aspidium OerstedA Heer, than any other.

Frond bipinnate or tripinnate, arborescent; rachis of the principal pinna stout and rigid; ultimate pinnae alternate, short, oblong-lanceolate,nbsp;terminating in an elliptical obtuse pinnule or lobe, which is similar to thenbsp;pinnules lower down on the pinna; lower pinnules distant, elliptical innbsp;shape, obtuse, attached by the middle of the much narrowed base, or bynbsp;the midnerve alone; upper pinnules attached by the entire widened base;nbsp;uppermost ones united towards the tip of the pinnae; all very thick andnbsp;leathery in texture; lateral nerves not distinct, but apparently simple, andnbsp;bearing the sori on their summits; sori pear-shaped or truncate-elliptical,nbsp;in two rows, one on each side of the midnerve; sterile forms not seen.

Only the fructified form of this fern was seen. The dehiscence of the sori seems to be marginal, and there are indications of the escapingnbsp;sporangia, as shown in PI. XIII, Fig. 9�, which represents a greatlynbsp;enlarged sorus. The plant seems to be a distinct new species.

Frond tripinnate, arborescent; rachises of the pinnm of various orders, strong and rigid; principal pinnae very large, spreading widely; penultimate pinnae alternate, in outline elongate-oblong or elliptical, acuminate,nbsp;abruptly and greatly narrowed towards the summit, slightly so towards thenbsp;base; ultimate. pinnae linear, acute, quite short, being longest towardsnbsp;the middle of the penultimate pinnae, at first rapidly shortened towards thenbsp;upper part and^ then gradually giving the acuminate terminations ofnbsp;the penultimate pinnae. The basal ultimate pinna on the lower side of thenbsp;penultimate pinnae is usually abnormally short and broad, being insertednbsp;in the angle made by the junction of the penultimate pinna with the principal rachis.

Towards the summit of the penultimate pinnae the ultimate ones pass through pinnae reduced to toothed pinnules into those which finallynbsp;become simple pinnules; pinnules varying according to position on thenbsp;frond, usually alternate, short, acute to obtuse, slightly falcate-ovate,nbsp;attached by a widened base; those from the lower part of the frond withnbsp;dentate or undulate margins, those from the middle portions with entirenbsp;margins, those from the summit of the pinnae of the various orders unitednbsp;to form teeth. The basal pinnule on the lower side of the ultimate pinnae,nbsp;inserted in the angle between the ultimate and penultimate rachises andnbsp;partly on the latter, differs from the normal pinnules in shape and size,nbsp;being heteroniorphous and larger than the normal one. It is furnished withnbsp;a lobe or tooth on the lower side. In the sterile forms the character of thenbsp;pinnules and of the nervation is that of Cladophlebis. The pinnules havenbsp;each a midnerve sending off alternately on each side slender but distinctnbsp;lateral nerves, simple or once forked. Fructified forms have the pinnulesnbsp;mostly obtuse, while those in the sterile portions are acute; the sori are

placed on the lower portion of the pinnules in a row on each side of the niidnerve, and extend nearly to the summits of the pinnules. They arenbsp;reniform, proportionally large, and inserted in the end of the upper branchnbsp;of a forking nerve.

Tliis beautiful fern is not very rare at Fredericksburg. It has afforded the most perfect specimens found of the ferns of the Potomac flora, and anbsp;sufficient number of them has been obtained to give a pretty good idea ofnbsp;the character of the plant. From the size of some of the specimens wenbsp;may conclude that it attained the dimensions of a tree, for all the specimens seem to be fragments of compound pinnae, which were probably notnbsp;of primary rank. PL XIV, Fig. 1, seems to show a portion of the uppernbsp;part of a compound pinna, and Fig. 2 to represent a portion of a penultimatenbsp;pinna coming from a part of the frond lower than Fig. 1, and hencenbsp;larger. Fig. 3 seems to show the summit of a compound pinna like Fig. 1,nbsp;and the same may be said of PI. XV, Fig. 2. Portions like PI. XIV, Fig.nbsp;5, and PI. XV, Fig. 4, appear to belong to the lower part of the frond,nbsp;v/here the pinnules begin to show division into teeth.

This plant is not very near any described fern. The sterile portion reminds one of Cladophlebis parva for this part of the fern belongs tonbsp;the type of Cladophlehis. The plant is a little like Aspidium Oer'stedi Heer,nbsp;but can not be identified with that species.

Frond bipinnate or tripinnate; arborescent ?; rachis of the principal pinna stout and rigid; pinnse of ultimate order reduced to pinnules in thenbsp;terminal portions of the penultimate pinme, alternate, linear lanceolate,nbsp;passing through pinnately lobed pinnae into pinnules with entire margins;nbsp;leaf-substance thick and leathery; nerves slender, immersed in the leaf-substance, and seen with difficulty; pinnules of the lower pinnse opposite,nbsp;separate to the base; attached by the entire base, elongate oblong, subacute, with denticulate margins; sterile form of the frond not seen; sorinbsp;comparatively small, reniform, in two rows, one on each side of the mid-MON XV-7

nerve of the pinnules, and placed at the summit of the upper branch of a-forking nerve.

This fern is soin3thing like the living species Nephrodium acutum Hook, and has no near affinity with any described fossil. As its sterilenbsp;form has not been found, its full character can not be made out.

Frond bipinnate or tripinnate, arborescent; in the sterile forms the principal rachis is stout, straight, and rigid; the ultimate pinnm alternate,nbsp;with a strong stiff rachis, linear-lanceolate, comparatively short; pinnulesnbsp;in sterile and fertile forms Pecopteris-like, closely placed, separate to thenbsp;base, opposite, rarely subopposite, linear, slightly falcate; leaf-substancenbsp;thick; sterile leaves in the lower part of the frond denticulate, towardsnbsp;the summit of the compound ultimate pinnae united and passing intonbsp;lobes; midnerve of sterile and fertile pinnules continuing to the summitnbsp;of the pinnules; lateral nerves of the sterile pinnules of the lower andnbsp;middle portions of the penultimate pinnm furcate towards the base of thenbsp;pinnules and simple towards their tips; in the upper pinnules mostly simple, in the fertile pinnules furcate, and bearing the sori on the end of thenbsp;upper branches.

In the fertile forms the principal rachis is comparatively slender, the ultimate pinnae are opposite and widest towards their middle, and quitenbsp;long; the sori are placed on the margin of the pinnules, unlike those of thenbsp;preceding species, which have them within the margin. The sori are comparatively large, reniform in shape, placed in a row on each side of thenbsp;midnerve, and in no case extend to the tips of the pinnules. They diminishnbsp;in numbers in passing from the pinnules of the lower part of the ultimatenbsp;pinnae to those of the upper portion, and disappear a little beyond the middle portion of the pinnae.

Localities: Entrance to Trent�s Reach; fishing hut above Dutch Gap Canal; Fredericksburg; hill-side near Potomac Run.

The fine specimens depicted in PI. XVII, Fig. 1, and PI. XVI, Fig. 3, come from the entrance to Trent�s Reach. The latter seems to be thenbsp;upper part of a compound pinna. The sori are comparatively large.nbsp;Nerves occur on all of the pinnules. They are most numerous on thenbsp;pinnules near the base of the ultimate pinnm, and are not present at all onnbsp;the pinnules towards the end of these pinnae. A noteworthy feature ofnbsp;the fructified pinnules is the fact that the basal ones are shorter and smallernbsp;than those towards the middle of the ultimate pinnae. In this feature,nbsp;and in the opposition of the ultimate pinnae, the fertile form differs fromnbsp;the sterile one. The plant seems to be not near any described form. It isnbsp;more like Aspidium Jenseni Heer, than any other.

Sterile fronds not seen; rachis of ultimate pinnae slender; pinnules alternate, attached by the middle portion of the base, crenately toothed,nbsp;obtuse; sori rather large, in two rows, one on each side of the midrib,nbsp;placed near the margin, on the summit of the uppermost branch of thenbsp;nerves ; subglobose in shape, similar to those of Cystopteris, with an inflatednbsp;indusium at base; nerves branching palmately in each tooth.

This pretty fern is very rare at Fredericksburg. It is much like the genus Cystopteris of the Aspidece. It does not seem to be nearly allied tonbsp;any described fossil.

(See Heer, Flor. Foss. Arctioa, vol. 6, Part 2, Foss. Flor. Gr�tilands, p. 30; vol. 7, p. 2.)

Pinnules narrowly linear, acute, with minute teeth directed forwards; nerves simple, parallel and ending in the teeth.

This plant, although found in only one small fragment, is quite distinct from all others of the Potomac flora. I unite it with Heer�s plant provisionally and with doubt, as the fragment is too small to give the full character

of the fern. It may be compared with that shown in Vol. VII of Heer�s work just cited, PI. XLVIII, Fig. 11.

Pinnules oblong, slightly falcate, acute, dentate; sori in a row on each side of the midnerve, on the summits of the single lateral nerves,nbsp;round to broadly elliptical in shape, comparatively large.

This is an Aspidium of the Didymochloena type. It may belong to some of the elsewhere described Potomac forms.

Plate XXI, Fig. 6; Plate XXIV, Fig. 8; Plate XXV, Fig. 10; Plate XXVI, Pigs. I, 14, 16, 17.

Frond bipinnate to tripinnate; ultimate pinnae alternate; pinnules, or reduced pinnae alternate to opposite, in the sterile portions small, oblong-lanceolate, acute, with winged rachises, pinnules or reduced pinnae of thenbsp;lower pinnae cut into ovate small lobes, the lowest ones being minutelynbsp;toothed, the upper pinnules also minutely toothed; nerves of the lowestnbsp;lobes or teeth composed of a midrib, which sends off on each side, alternately, simple nerves; in the upper lobes and teeth they are furcate; leaf-substance thin, and usually decurrent; in the fertile portions the pinnulesnbsp;or reduced pinnae are ovate-oblong, obtuse, with ovate-acute lobes, the twonbsp;lower being slightly dentate; nerves in the lower lobes simple, and alternately given off on each side of a slender midrib, those in the middle andnbsp;upper lobes several times or simply forked; in the sterile forms the basalnbsp;upper lobe of the pinnules or reduced pinnae usually larger than the othersnbsp;and directed upwards parallel with the penultimate rachis; sori subglobosenbsp;in the two basal lobes and situated on the summit of tire midrib and of allnbsp;the lateral nerves, but in the higher lobes mostly single in each lobe, andnbsp;placed on the summit of the upper branch of the lateral nerves.

Localities: Fredericksburg; red clay ball in the banks of the Dutch Gap Canal; fishing hut above this canal; rather rare at all places.

� This is an Aspidium of the Polystichum type. It does not seem to be near any described plant.

Frond unknown; probably bipinnatilid; reduced pinnae or pinnules, linear, cut pinnately nearly to the rachis into ovate-falcate obtuse lobes ornbsp;pinnules ; leaf-substance thick and leathery; sori in a row on each side ofnbsp;the midrib, elliptical in shape and small, placed on the simple lateralnbsp;nerves within the margin of the lobes.

This is another of the Aspidieae of the Didymochloena type. It is not nearly like any described fossil.

Plate XXII, Fig. 9; Plate XXV, Figs. 11, 12; Plate XXVI, Fig.s. 2, 8, 9, 18; Plate LIV, Figs. 3, 9.

Frond bipinnate or tripinnate, arborescent; principal rachis stout and rigid; ultimate pinnae alternate, sliort, linear-lanceolate; pinnules alternatenbsp;or subopposite, short, closely placed, narrowed at the base, cut more or lessnbsp;deeply into lobes or teeth which are ovate or oblong, obtuse or subacute,nbsp;very small, those of the fertile portions of the frond standing nearly perpendicular to the rachis and having in each lobe or pinnule a simplenbsp;lateral nerve which bears a sorus on its summit, those of the sterile and.nbsp;more common portions morp obliquely placed, mostly subacute, withnbsp;nerves in each lobe that fork simply in the upper ones, and in the lowernbsp;ones are composed of a midnerve with alternate simple branches; leaf-substance thick; sori very minute, club-shaped or elliptical, visible distinctly only with the help of a lens, and present only in the pinnules ofnbsp;the lower part of the pinnae, and mostly found on the lobes towards thenbsp;base of these.

Localities: Near Telegraph Station; red clay ball in the banks of Dutch Grap Canal; Fredericksburg; entrance to Trent�s Reach; fishingnbsp;hut above Dutch Grap Canal; rather rare at all localities.

This very finely exit fern is found most abundantly at the fishing hut above Dutch Gap Canal, but is not very common even there. The sorinbsp;are so small and the fertile pinnules so leathery that they can be seennbsp;only when the lower surface is uppermost. In PI. XXII, Fig. 9�, is givennbsp;a magnified pinnule with its lower surface uppermost; in Fig. O'* a similarnbsp;pinnule with its upper surface uppermost, and showing no sign of sori.nbsp;This latter is the common aspect of the plant. This may explain why thenbsp;sori were not seen by Dunker and Schenk. It seems to be certainlynbsp;Dunker�s species. The lobes in most of the specimens seem to be morenbsp;closely placed than in Dunker�s plant. It is one of the most widelynbsp;diffused ferns of the Potomac flora.

Frond tripinnate; principal rachis comparatively stout and rigid; ultimate pinnm alternate, very short, linear-lanceolate; pinnules membranaceous, alternate, lower ones separate to the base, upper ones united and reduced to lobes; lower pinnules broadly ovate, acute, narrowed to thenbsp;base, and subpetiolate, cut nearly to the midnerve into ovate, acute teeth,nbsp;reduced in the upper part of the compound pinnm to ovate, obtuse lobesnbsp;and teeth; sori very small, subreniform or globose, placed within the margin on the summit of the alternate simple lateral nerves; nerves in eachnbsp;of the pinnules and lobes, composed of a midnerve, with simple alternatenbsp;lateral ones on each side; in the uppermost, lobes the nerves become onenbsp;or more times forked, without a midnerve.

Localities: Red clay ball in banks of Dutch Gap Canal; hill-side near Potomac Run; near Telegraph Station; rare in most of the localities.

This pretty little plant is rather abundant at the locality on the hillside near Potomac Run. Forms such as Fig. 15 are quite common here, but as a rule show no fructification. The fructified specimen. Fig. 14, wasnbsp;found in the red clay ball in the banks of Dutch Gap Canal. Fig. 15 is anbsp;good deal like the smaller forms of Thijrsopteris Murrayana (Brongn. sp.)nbsp;Heer, but is no doubt a distinct species.

Sterile frond not seen; fertile frond showing only a skeleton imprint; principal rachis stout and rigid; plant most probably arborescent; racliisnbsp;of the ultimate pinnae stout and rigid; shape and dimensions of the pinnules not disclosed; apparently large, elongate-oblong, attached by thenbsp;entire base, alternate; midnerve rather slender, straight; lateral nervesnbsp;simple, and bearing at their summits the sori arranged in a row on eachnbsp;side of the midrib. The sori are very large, reniform in shape, and seemnbsp;to have been situated near the margin of the pinnules. Under a good lensnbsp;the sporangia may be seen arranged often in a band near the margin ofnbsp;the sori.

This plant seems to have been a tine large fern. It is seen only as an imprint on the surface of the fine clay, giving a skeleton of the more durable parts. The imprints of the sori are very distinct. The sterile form wasnbsp;not seen. This seems to be a species distinct from all described ones.

Frond tripinnate; sterile forms have the pinnae of ultimate order short, subopposite, with pinnules towards the base separate and rathernbsp;remote, slightly decurrent, obtuse, oblong and subopposite, but towards thenbsp;tips graduating into lobes and teeth which are ovate-obtuse; leaf-substance thick; lateral nerves in each pinnule or lobe composed of a midnerve, which on each side sends off alternately branches which fork or arenbsp;simple. Fertile portions of the frond have sometimes sterile and fructifiednbsp;pinnules on the same pinna, but usually the fructified pinnules are onnbsp;distinct parts of the frond, and then the specimens found show only thenbsp;skeletons of the sori and nerves, the sori by their arrangement giving thenbsp;outlines of the pinnules; sori very minute, visible distinctly only with thenbsp;help of a strong lens; rounded in shape, and arranged in a row on eachnbsp;side of the midnerve, placed at the summit of a simple lateral nerve.

They extend from the base to the summit of the pinnules. The arrangement of the sori indicates that the fructified pinnules in the lower pinnm are toothed or lobed, and that towards the summit of the compound pinnmnbsp;they graduate into lobes and teeth.

The fructified forms are the common ones, sterile forms are very rare. Numerous specimens, such as are depicted in PI. LIX, Fig. 12, and PI,nbsp;LX, Fig. 7, and smaller ones, may be found here, the pinnules beingnbsp;reduced to imprints of the sori and principal nerves. The plant seems tonbsp;be a very well marked new species.

The genus Pohjpodium, if it exists in the Potomac flora, is not represented by many' species. The imperfect preservation of the specimens does not permit the certain determination of the genus, but there are twonbsp;species which agree better with this genus than any other, and for thisnbsp;reason I place them provisionally in it.

Pinnules narrow and linear, obtuse; fragments of the fertile ones alone were seen ; leaf-substance very thick and leatheiy; sori very large,nbsp;globose in shape, placed on the ends of strong simple lateral nerves,nbsp;which are at their summits expanded into club-shaped receptacles arrangednbsp;in a row on each side of the midnerve of the pinnules, a little within thenbsp;margin, and extending nearly from the midnerve to the margin.

The pinnules of this plant seem to have' been narrow and long, very thick and leathery. The club-shaped summits of the nerves which supported the sori appear, when the upper surface of the pinnules is presentednbsp;upwards, showing through the leaf-substance as elliptical elevations, looking like sori, as shown in Fig. 5. Figure 4 represents, slightly enlarged, anbsp;fragment of a much longer pinnule with the lower side uppermost, showingnbsp;the character of the very large sori. A granulation is seen with the help

ot a lens ovei� the surface of the sori, as if caused by the sporangia. No indusium appeal's.

This fossil is a good deal like the living Fadyenia prolifera, and the specific name is chosen from this resemblance. It is a little like NatJiorstianbsp;anyustifolia Heer/ but is distinct from that plant.

Frond bipinnatifid; pinnae in the sterile forms of ultimate order, or pinnules linear-elongate, cut more or less deeply into broad, ovate, slightlynbsp;falcate, acute lobes or pinnules; midnerve of the pinnae strong and rigid;nbsp;nerves of the lobes or pinnae composed of a nerve-bundle formed by anbsp;parent nerve which goes off obliqu�ly and curves outward towards thenbsp;outer edge of the lobes, sending off branches only from the upper side;nbsp;the branches curved strongly outward, and each twice forked, except tlienbsp;upper one, which is once forked; fertile pinnae or pinnules serrate,nbsp;narrowly linear; nerve-bundles in each tooth branching and divergingnbsp;flabellately from the insertion, the lower branch forking several times, thenbsp;upper one simple and directed obliquely upwards, bearing on its summitnbsp;in each tooth am obovate sorus.

This seems to be a very distinct species. The lens shows a granulation over tho surface of the club shaped sori which seems to be caused by tlio sporangia.

The genus Acrostichum seems to be represented in the Potomac flora, by tlie small fragment described below. It also has near aillies in the newnbsp;genus Acrostichopteris, so abundant at Baltimore.

Frond and pinnm not seen; pinnules very obtuse, thick and leathery in texture; nerves not seen distinctly; sori small, in three double rows,nbsp;each row separated from its fellow by a pretty distinct line, which is

apparently a nerve. The entire under surface of the pinnule is covered by the sori.

Only a small fragment of this curious feim was found, and consequently little can be made out as to its true nature. It seems to be quite different from all previously described fossils.

Fronds probably creeping, with very long, often flexuous rachises, which seem to have been more or less succulent; pinnae going off obliquely,nbsp;long and appai�ently slender; ultimate pinnae or pinnules subopposite tonbsp;alternate, comparatively short, and cut down nearly to the rachis into morenbsp;or less cuneate-flabellate pinnules or primary segments. These are dividednbsp;generally into cuneate-flabellate segments, which in turn are separatednbsp;into oblong segments ending in oblong, or ovate-obtuse, or acute teeth;nbsp;pinnules decurrent and forming a wing; nerves slender but distinct,nbsp;flabellately diverging, forking dichotomously, and ending in the teeth;nbsp;fructification occurring on the basal segments of the pinnules, in the uppernbsp;portions of the frond on the upper one alone, in the lower portions onnbsp;the upper and lower ones, the fructified segments close appressed to thenbsp;principal rachis. The fructified segments are so modified as to take thenbsp;form of leathery, rounded, or elliptical segments, which on the lower sidenbsp;are covered by the naked sori, and seen from the upper side, especiallynbsp;when compressed on the clay, look like pods.

This curious genus of ferns seems to be of a composite character The sterile forms look so much like Baieropsis that before the fructifiednbsp;forms were found, which occur only at Baltimore, they were taken to benbsp;small forms of that genus.

The genus in the naked sori is like Poly^mlium, but in most features stands nearest to Acrostichmn, much resembling the section Rhipidopteris.nbsp;In this latter, however, the fructification is borne on separate pinnules. Ifnbsp;we place the fructified pinnules of Rhipidopteris as basal segments on thenbsp;sterile ones, we have a form stiikiivgh^ like Acrostichopteris. This genusnbsp;has also some resemblance to Marsilea.

Fronds with very long, more or less flexuons pinnae, apparently creeping; ultimate pinnae or pinnules subopposite to alternate, going off at a large angle and arching slightly away from the principal rachis, ending innbsp;one or two oblong lobes which have oblong blunt teeth. At base they arenbsp;cut into pinnules or segments which are cuneate, fan-shaped, and these innbsp;turn are cut into oblong segments, which end in oblong or ovate-subacutenbsp;teeth; the pinnules or segments, in ascending from the base of the ultimatenbsp;pinnm towards their summits, diminish in the number of segments; nervesnbsp;slender but distinct, flabellately diverging and forking dichotomously, thenbsp;ultimate branches ending in the teeth; fructification as in the genus, andnbsp;occurring on the basal upper lobe in the upper part of the frond. In thenbsp;lower parts of the same they are found on the upper and lower basal lobes;nbsp;the fructified lobes rounded or elliptical, and close appressed to the principal rachis.

Localities; Abundant at Belt and Covington sti�eets, Baltimore; most common at the first-named locality.

PI. CLXXI, Fig. 1, seems to represent a sterile form. This comes from Belt street. Figure 7 of the same plate has both of the basal lobesnbsp;fructified. Tliis comes from Covington street. Figure 5 of the samenbsp;plate has only tlie fructified lobes retained on the principal rachis.

Plate XCIV, Fig. 4; Plate CLXX, Fig. 11; Plate CLXXI, Figs. 2, 6; Plate CLXXII, Fig. 13.

Principal rachis slender; ultimate pinnae or pinnules densel)^ crowded, often overlapping, very broad in proportion to their length, lower onesnbsp;sometimes abnormadly short and wide as compared with those higher uji,nbsp;being broad, fan-shaped in outline; primary segments or pinnules diminishing towards the ends of the ultimate pinnae in the number of segments;nbsp;lower pinnules or segments cut into two or three main lobes, narrowlynbsp;oblong or ovate, ending in minute teeth; nerves as in generic description;nbsp;fructification on the lower basal lobe or on both; fructified lobes ellipticalnbsp;in shape and proportionally very large.

Localities: It is common on both Belt and Covington streets, Baltimore, and is rare at the fishing hut above Dutch Gap Canal.

Only the sterile form, PI. XCIY, Fig. 4, was fovmd at the last-named locality. Fructified forms are the most common ones at Baltimore, andnbsp;the same is true of the preceding species, A. longipennis.

Principal rachis comparatively very stout and rigid ; ultimate pinme or pinnules short, remote, small; pinnules or segments of the first ordernbsp;cut normally into two lateral lobes and one terminal one, the latter largest,nbsp;minute ,� the principal lobes diverge flabellately, each being cut normallynbsp;into two oblong lobes, which end either in very short acute triangular teeth,nbsp;or in oblong o'r ovate-obtuse to acute ones; nerves forking dichotomoiisly,nbsp;flabellately diverging, the ultimate branches ending in the teeth.

Localities: Belt and Covington streets, Baltimore ; although rare there, the most abundant species of the genus at the fishing hut above Dutchnbsp;Gap Canal; rare at the entrance to Trent�s Reach.

Ultimate pinnae or pinnules very short, terminating in a three-lobed segment or pinnule; principal segments or pinnules rapidly diminishing innbsp;ascending in the number of segments or lobes; the lowest pinnules ornbsp;principal segments narrow and cuneate at base, as are all, mostly cutnbsp;deeply into two unequal lobes, the upper ones being the smaller, both subdivided one or more times into strap-shaped lacinim, which end in narrowly oblong obtuse teeth; nerves forking repeatedly in a dichotomousnbsp;manner, so that the ultimate branches end in the teeth; fructified forms notnbsp;seen.

Localities: Fishing hut above Dutch Gap Canal; road-side near Potomac Run; rare.

The oiie shown in Fig. 11 from the Dutch Gap locality differs somewhat from that in Fig. 6 from the same locality and from that in Fig. 7

from near Potomac Run, but the difference is not sufficient to separate them. Figure 14 gives, magnified, a complete leaf corresponding to thosenbsp;of Fig. 7, but more complete than any found on that specimen.

Pinnules rounded, fan-shaped, cyclopteris-like in form, divided to the base into three principal lacinim, which in turn are subdivided at differentnbsp;distances from the base into subordinate lobes; lacinise all oblong, diverging flabellately, the principal ones cuneate at base; they end in obtusenbsp;oblong teeth, which are quite narrow; nerves obscure, but, as in the generic description, dividing repeatedly in a dichotomous manner from thenbsp;base and diverging flabellately, so that the ultimate branches end in thenbsp;teeth; fertile forms not seen.

Several specimens of this plant were found, but they appear only in the form of detached pinnules, one of the largest of which I have figured,nbsp;ft has a small bit of the rachis still attached. This plant shows a numbernbsp;of detached pinnules lying as if they had fallen from the same plant. Itnbsp;is more like Baieropsis than any of the species of Acroetichopteris, and in itsnbsp;fragmentary state, with fructification not shown, it may belong to thatnbsp;genus of conifers.

The genus Asplenium found by Heer so abundant in the Jurassic flora of Siberia is not determined positively in the Potomac flora. The speciesnbsp;described below�A. diihium�quite possibly may belong to the tribe ofnbsp;the Aspidiece, being found in the section with oblong sori as in Fadyenia.

Frond bipinnate or tripinnate; pinnules oblong, subacute, separate to the base, alternate, nearly at right angles with the rachis: nerves furcate,nbsp;bearing tlie sori on the end of the upper branch, sori elliptical, in a row

This plant is in too fragmentary a condition to make out its true chai*' acter. The shape of the pinnules is something like that of those of Bunker�s Neuropteris Albertsii. The plant is quite near to Asplenium argutulumnbsp;Heer.^

Fronds bipinnate or tripinnate; pinnules varying much in size and shape, mostly oblong, ovate-lanceolate, or oblong-obovate, decurrent andnbsp;mostly confluent at base, coriaceous; primary nerve of the pinnules dissolved before attaining the apex into many dichotomous nerves; secondarynbsp;nerves going off at a very acute angle, diverging in ascending, severalnbsp;times dichotomous.

The description given above for the genus is very nearly that given by Schimper. There are several species of ferns in the Potomac floranbsp;which would come under the group having these characters. The plants,nbsp;however, are not common, except at the 72d mile-post, near Brooke, wherenbsp;Thinnfeldia variahilis is the most common fern.

Frond bipinnate or tripinnate; rachises of the pinnse stout, arborescent ; pinnules lobed or toothed, with mostly ovate-obtuse lobes or teeth, short, varying much in size and nature according to position on the frond,nbsp;passing in ascending, in the upper part of the pinnae, through toothed andnbsp;undulate pinnules into entire ones; lower pinnules attached by the rachisnbsp;alone, and deeply cut into broadly ovate-obtuse lobes; up higher in thenbsp;pinnae and on the frond they have ovate teeth and are attached by thenbsp;middle of the much-narrowed base, and are slightly decurrent; towardsnbsp;the top the ultimate pinnae pass into crenately lobed segments and thesenbsp;into lobed and toothed pinnules, like those lower down; all are acute;

'Flor. Foss, Arc., vol. 4, pt. 2, Beitrage zur Flor. Ostsib., PI. Ill, Fig. 7; PI. XIX, Figs. 1-4.

leaf-substance thick and leathery; midnerve neuropteris-like, and vanishing before attaining the apex of the pinnules; lateral nerves occur in the lower portions of the pinnules mostly in nerve groups; all go off verynbsp;obliquely and fork usually several times, very fine and closely placed, butnbsp;distinct.

Localities: 72d mile-post, near Brooke, common, and the most abundant fern; road-side near Potomac Run; rare.

All tlie specimens figured, except that in Ph XVIII, Fig. 6, come from the 72d mile-post, near Brooke. Strange to say, while the plant is abundant at the 72d mile-post, not a trace of it can be seen at the �bank� nearby,nbsp;This is a striking illustration of the localization of the species in tliis flora.

Taken as a whole this Thinnfeldia is unlike any described fossil. Some of the pinnules in shape remind one of T. rhomboidalis Ett., givennbsp;by Schenk.^

Frond bipinnate or tripinnate; rachises comparatively stout; leaf-substance thick; pinnules varying in size and shape with their position on the piniuB and frond; in shape they are ovate-elliptical to subrhombic, thenbsp;lower ones irregularly cut into oblong to elliptical lobes; the lower surfacenbsp;of the pinnules has a very fine granulation between the nerves, which cannbsp;be seen distinctly only by the help of a lens; nerves closely placed, verynbsp;fine but distinct on the under surface of the pinnules, repeatedly branchingnbsp;and diverging flabellately.

Localities: Fishing hut above Dutch Giap Canal, and road-side near Potomac Run; rare.

The plant occurs more commonly at the former locality, where several specimens were found. It is very rare at the locality near Potomac Run.

Frond bipinnate or tripinnate; principal rachis rather stout; pinnules with thick texture, alternate, broadly ovate in outline, obtuse, cut more or

less deeply into sub rhombic or broadly elliptical and rounded lobes; nerves numerous, closely placed, slender but distinct, repeatedly branching'nbsp;in the lower lobes, and diverging flabellately; midrierve in the terminalnbsp;lobe dissolving in branches some distance below the summit, and in itsnbsp;lower portion sending off very obliquely nerve bundles or branches whichnbsp;fork one or more times.

This plant in some of its forms is something like T. yranulata, but it shows none of the granulations and the pinnules are more obtuse.

Frond large, bipinnatifid; rachis slender and narrowly winged; pinme subopposite; segments of the pinme long, linear, bluntly terminated, showing the same width and structure as the parts to which theynbsp;are attached; that is, a slender, narrowly winged midnerve, segments sometimes forked at their tips. This descripti ni given by Schimper* agreesnbsp;well with one of the Potomac species, and for this reason I place it provisionally in Saporta�s genus.

Frond unknown; lobes of the pinnules or pinnm of ultimate order, forking at the ends or simple; pinnules and lobes coriaceous, strap-shaped,nbsp;subacute, having a single slender nerve.

This plant agrees with Saporta�s genus Stenopteris^ which contains, as tar as certainly made out, only the single species 8. desmomera. Thenbsp;description, however, which makes the midnerve narrotvly wdnged does notnbsp;apply, as the laminae on each side of that nerve in tlie Potomac plant arenbsp;comparatively wide. Only a single specimen was found at the Brookenbsp;locality.

Frond simply pinnate; pinnules long, linear, more or less narrowed towards their ends, rounded at the base or nearly heart-shaped, attachednbsp;to the principal rachis by the midnerve alone, which sometimes' forms anbsp;disarticulating short pedicel; midnerve strong, lateral nerves going offnbsp;obliquely and abruptly, taking a horizontal position or bent somewhatnbsp;obliquely upwards, simple and forked.

This description given by Schimper^ agrees exactly with a number of species found in the Potomac flora. Angiopteridium is a characteristicnbsp;Jurassic type, and the number of species of this genus occurring in thenbsp;Potomac flora adds decidedly to the Jurassic element otherwise so stronglynbsp;represented in this flora.

Frond pinnate; pinnules thick and leathery, long linear, subacute, remotely placed, free to the base, auriculate at base, attached by the midrib alone; auricles of the bases of the pinnules overlapping the upper surface more or less ; midrib of pinnules rather stout and rigid; lateral nervesnbsp;often obscurely shown, fasciculate or bifurcate, and towards the tips simplynbsp;forked.

The plant is rare at each locality, but is most common at Fredericks burg. It is something like Pteris longipennis Heer,^ but there is no reasonnbsp;to think that it is a Pteris. It resembles Pecopteris saUcifoUa,^ Oldham andnbsp;Morris. The forms figured in Figs. 8, 9, 11 occur at Fredericksburg;nbsp;Fig. 10 occurs at the locality near Potomac Run. This is different fromnbsp;the others in the great length of the pinnules and in the fasciculate nerves,nbsp;which are bifurcate, with the branches again forking near their tips. Thenbsp;nerves are obscure on the upper surface of the pinnules. The main rachisnbsp;is stout and keeled on the under surface, as is shown in Fig. 9. On the

upper surface the auricles at the base of the pinnules overlap more or less the surface of the main rachis.

Fi'ond unknown ; pinnules seen only in fragments, hnt apparently long, 3.5��wide; midnerve comparatively very slender; leaf-snbstancenbsp;comparatively thin; lateral nerves slender but distinct, going off at annbsp;angle of over 45'�, arched backwards slightly for a short distance from tlienbsp;midrib, and then inclined forward towards tlie tip of the pinnules; simplenbsp;or forking at various distances between the midrib and margin.

This plant was found in only a few small fragments. The nerves on the right-hand, half of the figure are distorted by pressure. They arenbsp;shown in their normal position in the left-hand half. It is something likenbsp;Toeniopteris Stenoneura Schenk,^ and also Tceniopteris tenuinervis Brauns,nbsp;as given in Figs. 3, 4, of the same plate, but it is larger than either, andnbsp;has the nerves more dichotomous than the last. It is also a little likenbsp;Tceniopteris vittata Brongn. It has nearly the nervation of Angiopteridiumnbsp;McClellandi of the Indian flora.

Frond unknown; pinnules elliptical, length, 37��, maximum width 15��; leaf-substance membranaceous; midnerve comparatively very stout;nbsp;lateral nerves slender but very distinct, going off at an acute angle andnbsp;then obliquely ascending to the margin, mostly forked at or near the base,nbsp;branches simple and nearly parallel.

This is a very distinct but unusually small plant. It seems to be nearer to Stangerites ensis Oldham and Morris, than any other. This hasnbsp;been made an Angiopteridium by Schimper. Possibly this may be a youngnbsp;leaf of some of the species described under another name in the Potomacnbsp;flora.

Only a small fragment of a pinnule seen; midnerve slender; lateral nerves slender, closely placed, going off at an acute angle and maintainingnbsp;the same direction to the margin, nearly parallel, forked at the base ornbsp;above.

Frond unknown; pinnules apparently long and proportionally quite narrow; midrib stout and prominent; leaf-substance thick, shining, andnbsp;leathery, hiding the lateral nerves on the upper side.

Only a fragment of a pinnule was found, so that its length could not be made out. The specimen probably presents the upper surface of thenbsp;leaf uppermost.

Frond unknown; pinnules ovate, broad and rounded at base, truncate and serrately toothed at the tip; maximum width, 36��; length, 8��;nbsp;midnerve stout at base and split up into branches at the summit; leaf-substance membranaceous; lateral nerves slender but very sharply defined,nbsp;remote, going off at an acute angle, arched backward near the base andnbsp;forward higher up, forked near the base or above, branches slightly diverging, mostly simple, very rarely forked near the margin.

This is a very rare plant, but a distinctly defined one. The two specimens figured were so placed as to indicate that they belonged to thenbsp;same pinnule. Fig. 7, representing the tip, corresponding to Fig. 6.

This plant is more like Macrotmniopteris ovata Schimper, Tceniopteris ovalis Oldham and Morris, from Bindrabun, India, than any other describednbsp;fossil. The apparent stipe in the plant of Oldham and Morris seems tonbsp;be simply a portion of the midnerve stripped of the lamina of the pinnule.

Frond pinnate; principal rachis stout and rigid; pinnules elongate-lanceolate; midnerves strong, rounded, and prominent; leaf substance thick; lateral nerves closely placed, forked mostly at their insertion,nbsp;rarely higher up, sometimes simple, branches simple and parallel, archednbsp;near the base strongly backward and above curved slightly forward, thinnbsp;but distinct.

Although rare, this is the most common species of the genus at Fredericksburg. In the shape of the pinnules and in the course of thenbsp;lateral nerves it is something like Oleandridium tenuinerve Schimper,nbsp;Tceniopteris tenuinervis Brauns, as figured by Schenk,^ but that is a simplenbsp;frond.

Frond unknown; pinnules larger than in the normal A. strictinerve, in some cases, as in Fig. 5, attaining the width of 44��; midrib comparatively stout; lateral nerves fine but distinct and sharply defined, oftennbsp;simple, forking at the base or higher up, branches simple and parallel,nbsp;arched backward in the lower portion of the lateral nerves and thennbsp;inclined forward.

This plant is in some points similar to Angiopteridium nervosum, described elsewhere, but the nerves are finer and more closely placed. Innbsp;Fig 1 there are two fragments of pinnules so placed as to indicate thatnbsp;they belong to the same frond, coming off pinnately from a commonnbsp;rachis.

Frond pinnate; leaf-substance thin; pinnules oblong-ovate, abruptly narrowed at their tips, margins finely serrate, sometimes with double teeth;nbsp;midnerves strong towards their bases and attenuate towards their summits,nbsp;and near the apex splitting up into branches; lateral nerves going off at anbsp;very oblique angle and curving out to meet the margin, simply forked ornbsp;several times forking, slender but distinct.

This plant in the general shape of the pinnules and the nervation is much like the Neuropterids of the Carboniferous era, and is peculiar innbsp;the fine toothing of the margin. I place it provisionally in the genusnbsp;Anfjioptericliim, but possibly this and A. ovatum should be made a new genus.nbsp;This plant seems to be a type between Thinnfeldia and Angiopteridium.

Frond bipinnate or tripinnatifid; pinnules linear-lanceolate, or oblong, acute to obtuse, lobed or toothed, sori proportionally very large, elongatenbsp;to narrowly elliptical, in a row on each side of the midrib, one in each lobenbsp;or tooth, inserted on thick supports or segments, which represent the transformed segments or lobes, placed on the anterior margin of these, and running down nearly their entire length. Type, Aspleniopteris pinnatifida.

This curious type of fern differs in some respects, from all described fossils. The most noteworthy feature is the contraction of the lobes ornbsp;teetli of the pinnules into thick leathery supports which bear the long narrow sori on their anterior margins, the general shape and position of thenbsp;sori resembling those features in Asplenium. Aspleniopteris pinnatifida maynbsp;be taken as the type, that being pretty fully represented in the parts found.nbsp;The genus may be compared with Bicksonia clavipes, Heer,^ but, unlikenbsp;that plant, the sori are long, narrow, and not borne always on the summitnbsp;of the modified lobes. The genus seems to be a composite type, unitingnbsp;the features of Pteris, Asplenium, and Osmimda, resembling the latter in

the reduction of the lobes to mere supports for the sori. The singleness of the sori in the lobes, their great size, and anterior position form peculiarnbsp;features.

Frond tripinnatifid; rachis of the primary pinna or of the frond very stout, rigid, and straight; pinnae or pinnules alternate, varying much innbsp;length according to position, with strong rigid rachises; sterile pinnulesnbsp;linear-lanceolate, subacute, lower ones very long, much diminished innbsp;length in ascending, cut more or less deeply into crenate and roundednbsp;teeth and lobes; lateral nerves in each lobe flabellate diverging, with thenbsp;branches forked or simple, nerves very strong and distinct; fertile pinnae ornbsp;pinnules very long, with strong rigid rachises, linear, subacute ; lobes ornbsp;teeth reduced to thick leathery supports, which bear the narrowly ellipticalnbsp;sori on the anterior face ; the sori very long, almost as long as the lobes,nbsp;standing one in each lobe, apparently included between the two branchesnbsp;of a nerve that forks at the insertion.

This remarkable plant is rare. I can not feel sure that the sterile forms. Figs. 1-3, with rounded lobes belong to the same species with thenbsp;form depicted in Figs. 6, 7, possessing narrow subacute fructified lobes,nbsp;but the nervation and general character of the segments of the pinnaenbsp;indicate that they belong to the same species. The partially fructifiednbsp;form PI. XXII, Fig. 7, has the lobes on the upper side mostly sterile, indicating how they are modified in the development of the sori.

Sterile frond not seen; fertile frond bipinnate or bipinnatifid; pinnules or lobes reduced to leathery thick pedicels or. supports, which bear on their anterior or upper margin narrowly elliptical or oblong sori; sorinbsp;proportionally very large.

This small plant was found in too fragmentary a condition to permit its full character to be made out. It has some features that resemble thosenbsp;of Adiantum, especially the terminal position of the elongate sori on thenbsp;basal upper lobes and the two terminal segments. The basal upper segment is much larger than the others, and, unlike them, is subdivided intonbsp;several segments, which bear the sori on the tips of the lobes.

The genus Gleichenia seems, if present at all in the Potomac flora, to be very feebly represented. In this respect the Potomac flora differsnbsp;greatly fi-om that of nearly the same age described by Heer as comingnbsp;from Kome, Greenland.

Frond unknown; pinnae linear, narrow ; pinnules in the lower part of the pinnae separate to the base, in the upper portion united at base, oblong-obtuse, minute; nerves of the pinnules distinct, consisting of a midnervenbsp;which sends off alternately lateral nerves, which in the lower part of thenbsp;pinnules are forked, but in the upper portion are simple.

This plant is found only in small fragments. In the absence of fructification its identification with Gleichenia is not certain. It is very much like G. NordensM�kli Heer.^

This small fragment is too incomplete to justify a description. It reminds one of Asplenium Dicksonianmn Heer.^

Sterile nbsp;nbsp;nbsp;and fertile pinnules dimorphous; sterile frondnbsp;nbsp;nbsp;nbsp;decompound;

pinnules constricted at base, cut into lobes or teeth; nerves, nbsp;nbsp;nbsp;lateral ones,

g-oing off obliquely or under an acute angle; fertile pinnae contracted; sori globose, paniculate or racemose, inserted on a pediceled involucre.

This description, given by Heer^ for the genus Thyrsopteris, so far as the portion pertaining to the sterile frond is concerned, agrees well with anbsp;large number of species in the Potomac floi�a. These I place provisionallynbsp;in the genus Thjrsopteris, on accoixnt of the gi�eat resemblance that thenbsp;shape of the pinnules, the lobing, and the nervation show to the sterilenbsp;forms of various species determined to be Tliyrsopteris by their fructification. As, however, no fructification is found in the Potomac species, thenbsp;placing of these plants in the genus must be regarded as provisional. It isnbsp;quite possible that some of them belong to Aspidimn and Bicksonia. Thenbsp;genus Tliyrsopteris seems to be eminently a Jurassic type of fern. However it may prove to be with the fructification of the various speciesnbsp;assigned in this memoir to this genus, it is probable that they are at leastnbsp;distinct and true species. The great variety and comparative abundancenbsp;of these forms show that this type was developed in the Potomac flora tonbsp;an unusnal degree. They surpass all other types, even that of Cladoplile-bis, and give a decided Jurassic facies to the assemblage of ferns foundnbsp;in this flora. Even if we can not by fructification determine the affinitiesnbsp;of fossils with living plants, the lai�ge development of sterile forms of well-marked types is of importance in fixing the character of a flora.

It should be noted that a number of the species of Tliyrsopteris described in the following pages show a good many features similar tonbsp;those of 'Sphenopteris Mantelli, as described by Schenk and Heer.

Frond not seen; pinnse of ultimate order, linear-lanceolate, acute, narrowed to a petioled base, and cut very obliquely into oblong lobes, the lower of wliich are obtusely dentate; rachis of ultimate pinnules verynbsp;slender; lateral nerves in each lobe flabellate, sending off branches whichnbsp;in the lower lobes are once or twice divided, in the upper ones forked ornbsp;simple, rather remote, very distinct and strong.

This plant is not unlike the undetermined plant PI. XXI, Fig. 12, and may he the same. The fragments found are too small and rare to permitnbsp;its true nature to be made out. It is a little like Ileer�s plants, Adiantitesnbsp;Nynvpharmn, and DicJtsonia {Asplenimn) Johnstrupi.

Frond bipinnate or tripinnate; rachises slender; ultimate pinnae long, going off at a large angle and slightly curved upwards, linear, alternate;nbsp;pinnules all very short in proportion to their width, lower ones separate tonbsp;the base, upper ones united to form a narrow wing; pinnules much narrowed at base, cut obliquely more or less deeply into lobes or teeth according to position on the frond; lobes of the lower pinnules cuneiform or narrowed at base, very obtuse, fan-shaped and emarginate; of the upper ones,nbsp;oblong or ovate, very obtuse, towards the ends of the pinnae reduced tonbsp;oblong or ovate blunt teeth or lobes; nerves in the lower lobes of thenbsp;lower pinnules flabellate, remote, forking once or twice in the upper lobesnbsp;of the lower pinnules, and in the upper pinnules single, all quite distinct.

This well characterized and elegant little plant is near to Sphenopteris dissocialis Phillips. It reminds one also of Sphenopteris hymenophylloidesnbsp;Brongn.

Frond bipinnate or tripinnate, arborescent?; leaf-substance thick; rachises narrowly winged; compound pinnae terminating in a lobed acutenbsp;segment; ultimate pinnae or pinnules opposite or subojiposite, reducednbsp;towards the ends of the compound pinnae to dentate pinnules, and at thenbsp;summit to united lobes; united at base to form a narrow wing, those ofnbsp;the lower part of the frond cut deeply into oblong or subquadrate spiny-toothed lobes or pinnules; those higher up have obliquely cut lobes and

teeth of varying depth, the basal ones subquadrate or ovate and spiny-toothed ; the ultimate pinnae or pinnules gradually diminish towards the ends of the compound pinnae; the nervation in the pinnules and lobesnbsp;rather variable according to the position of the part, remote, very distinctnbsp;and strong; the lower pinnules and lobes have a midnerve sending off onnbsp;each side alternate branches either forked or simple, in the upper onesnbsp;either once forked or simple.

Localities: Fredericksburg; hill-side near Potomac Run; red clay ball in banks of Dutch Gfap Canal; rare.

This handsome plant is characterized bv its subquadrate, acutely dentate lobes and pinnules, and by the remoteness and strength of the nerves in them. It is not common at the localities where it is found. It is nearnbsp;to Phillips�s Sphempteris affinis.

Plate XXV, Figs. 4, 5, 16; Plate XXXVII, Figs. 2, 4; Plate XXXIX, Fig. 5; Plate XL, Fig. 6.

Frond bipinnate or tripinnate, arborescent; principal rachis flexuoiis, rather slender; ultimate pinnm alternate, remote; pinnules alternate ; leaf-substance thick, very obliquely inserted on the rachis, in shape oblong-acute, in the lower ones cut rather deeply into snbrhombic basal lobes,nbsp;which toward the tips of the pinnules pass into ovate or elliptical lobes andnbsp;teeth, in the upper ones cut into elliptical acute lobes and teeth; the pinnules narrowed at base nearly or quite into a petiole; nerves very distinct,nbsp;slender, closely placed, going off from the midnerve very oblique! jq diverging flabellately into each lobe and tooth, deeply forked, forking repeatedly, the branches subparallel.

This is a very fine fern, and although the fragments found are not large, they evidently belong to plants that must have attained very considerable dimensions. It has some similarity to Thyrsopteris priscAi Heer.nbsp;The fragment shown in PI. XXV, Fig. 16, has longer and narrower lobesnbsp;than the normal forms and may be different.

Plate XXVI, Figs. 6, 7; Plate XLIII, Figs. 4-6; Plate XLIV, Figs. 1, 2, 5; Plate XLIX, Fig. 2; Plate

Frond tripinnate, arborescent; principal rachis and that of the penultimate pinnge strong, rigid, straight; that of the ultimate pinnae rather slender; penultimate and ultimate pinnae alternate; ultimate pinnae morenbsp;or less distinctly petioled, linear-lanceolate, acute; pinnules diminishingnbsp;in size from the base to the tips of the ultimate pinnae, passing fromnbsp;toothed pinnules separate nearly to the base, through entire pinnules morenbsp;fully united, to lobes at the summit of the pinnae; pinnules linear tonbsp;narrowly elliptical, acute, obliquely placed, decurrent, and united at basenbsp;to form a wing of varying width, thick and leathery, narrowed at base,nbsp;those of the lower portion of the frond and of the pinnae minutely dentate;nbsp;towards the summit of the compound pinnae the ultimate pinnae reducednbsp;to lobed and toothed pinnules ; nerves of the pinnules of the normal kind,nbsp;composed of a distinct midnerve, which sends off alternately into each lobenbsp;or tooth a single nerve.

Localities: Fredericksburg; 72d mile-post, near Brooke ; White House Bluff; entrance to Trent�s Reach.

This fine plant is pretty widely distributed, and at White House Bluff it is by far the most common fern. The forms depicted in PI. CLXIX,nbsp;Figs. 6, 7, come from this place, and are plaiidy but small portions ofnbsp;what were once large fragments. The plant is not common at the entrancenbsp;to Trent�s Reach. PI. XLIV, Fig. 2, gives, slightly restored, a fine specimen found here. Fig. 1 of the same plate, and PI. XLIX, Fig. 2, givenbsp;two very good specimens which come from Fredericksburg. The firstnbsp;named seems to be the upper part of the compound pinna depicted in thenbsp;last-named figure. The princijial rachis seems to have been keeled ornbsp;ridged on the under side.

This plant is one of the 8j)henopteris Mantelli type, and perhaps by some would be united with that species, biit it is more robust, and thenbsp;pinnules are more like those of the Tliyrsopteris tvpe. It looks in somenbsp;points a good deal like Sphenopteris lonyifolia, Hunker (Mon. Weald., PI VIII,nbsp;Fig. 4), which Schenk unites with S. Goepperti. It however differs from S.

Gcepperti in the leathery texture of the pinnules and in other points. In the cutting of some of the pinnules there is a good deal of likeness tonbsp;T. elegans, Kunze, the living species and the sole survivor. It may also benbsp;compared with Asplenium Bicksonianum Heer.^ It resembles more thannbsp;any other described fossil Thyrsopteris elongata Greyler.^

Plate XXXIV, Pig. 3; Plato XXXVI, Pig. 2; Plate XXXVII, Pig.s. 3, 9; Plate XXXVIII, Pig. 1;

Frond tripinnate; leaf-substance thin; penultimate pinme mostly opposite, short; rachises slender, terminated by an obtusely lobed segment; lower ultimate pinnse pinnate, with basal pinnules three lobed,nbsp;passing towards their tips abruptly through entire pinnules into lobes morenbsp;or less united, short; towards the upper part of the frond and compoundnbsp;pinnae tlie ultimate pinnae pass rapidly into pinnules and lobes that arenbsp;more or less united; nerves departing in groups or nerve-bundles intonbsp;each lobe or tooth, flabellately diverging, and branching several times,nbsp;slender but rather distinct.

Localities: Red clay ball in banks of Dutcli Gap Canal; fishing hut above Dutch Gap Canal; Baltimore, collected by Meek; Deep Bottom.

This plant in facies is more like a Sphenopteris than any of the species united under Thyrsopteris, and this feature is dependent in part on thenbsp;shortness of the ultimate pinna; and the abrupt passage from lobed pinnulesnbsp;to united lobes. It is comparatively abundant among the plants collectednbsp;by Meek at Baltimore, but is rare at the other localities. There are anbsp;number of these species with Sphenopteris facies found in the Potomacnbsp;flora which differ sufficiently to forbid their union in one species. Theynbsp;may be noted as Thyrsopterids with a Sphenopteris facies.

Frond unknown, probably tripinnate; principal rachis narrowly winged, very slender, somewhat flexuous; ultimate pinme alternate, short,

�Fos8. Pfl. Juraform. Japans Palteontographica, vol. 24,1677, PI. XXX, Pig. 5 ; Pi. XXXI, Figs. 4, 5.

with a winged rachis; lower pinnules with oblong lobes rounded at the ends, cut very obliquely and more or less deeply, passing towards thenbsp;tips of the ultimate pinnae into oblong-obtuse lobes all minutely toothednbsp;on the summits or terminal margins; nerves distinct, diverging flabellatelynbsp;in each lobe and forking several times; the midnerve of the pinnulesnbsp;splitting up towards its summit.

This plant in the position of the toothing resembles Sphempteris acrodentata, but the lobes are narrower and the rachises winged, charactersnbsp;not found in that species.

Frond tripinnate; principal rachis slender, slightly flexuous; ultimate pinnae remote, alternate, sliort; penultimate pinnai terminating usually innbsp;a tliree-lobed segment; pinnules of the lower part of the frond and compound pinnse cut more or less deeply and quite obliquely into oblong ornbsp;ovate lobes, the two basal lobes being cut down nearly to the midnerve,nbsp;often with three teeth, diverging more or less widely. Towards the tip ofnbsp;the ultimate pinnm and the summit of the frond the pinnules pass throughnbsp;toothed elliptical pinnules into simple pinnules and lobes; midnerve of thenbsp;pinnules splits up at the tip into branches; nerves go off obliquely intonbsp;each lobe or tootli, comjiosed in tlie lower ones of a midnerve, whicli sendsnbsp;off alternately on eacli side branches forked or sinqile, composed in thenbsp;upper ones of 'forking and simple nerves.

Localities: Fishing hut above Dutch Grap Canal; Fredericksburg; red clay ball in banks of Dutch Gap Canal; rather rare.

This plant is noteworthy for the peculiar divergence of the two lowest lobes in the pinnules and tlie extreme slenderness of tlie primary racliis. Itnbsp;is not common, and appears not to be nearly allied to any described fossil.

Frond tripinnate, arborescent; pinnse and pinnules much crowded; rachises, especially the principal ones, as a rule, very stout; ultimate

pinnae alternate or subopposite, short, and in the lower portion of the frond spreading; pinnules in the basal portion of the ultimate pinnae, in thenbsp;lower part of the frond, cut deeply and obliquely into subacute, elliptical,nbsp;or subrhombic lobes, passing in the upper part of the ultimate pinnae andnbsp;of the frond tlirough round-lobed pinnules into entire elliptical and acutenbsp;ones, and finally into lobes of the same shape ; nerves in each lobe flab-ellately diverging, composed of a midnerve which sends off alternately onnbsp;each side branches either forked or simple.

Localities; Baltimore, collected by Professor Meek; Fredericksburg; fishing hut above Dutch Gap Canal; one small fragment from Covingtonnbsp;street, Baltimore; rare at most localities, but one of the most commonnbsp;ferns in Meek�s collection made at Baltimore.

This is a Potomac TJiyrsoptericl of the Sphenopteris type. In some features it is like certain Potomac plants described under other names.nbsp;In lobing it is somewhat like Thyrsopteris hrevipennis, but the facies isnbsp;quite different, the rachis is stouter, the lobes and pinnm are more acute,nbsp;elongate, and crowded.

Plate XXXVIII, Figs. 5-7, 9; Plate XLIII, Fig. 8; Plate XLIV, Fig. 3; Pl.ate XLVII, Fig. 4; Plate XLVIII, Fig. 1; Plate LIV, Figs. 2, 11; Plate LV, Fig. X ; Plate LVI, Figs. 1, 3.

Frond tripinnatifid, arborescent!; rachises comparatively slender; pinnae and pinnules subopposite to alternate; pinnules of the lower partsnbsp;of the compound pinnae cut deeply and very obliquely into narrowly elliptical acute lobes or teeth; pinnules of the upper portions passing throughnbsp;those with elliptical or ovate teeth into entire ones; nerves as in T. Meekiana, but less spreading and not so copiously branched.

Localities: Baltimore, common in the plants collected by Meek, occurring on tlie same pieces of shale with T. Meekiana, and almost asnbsp;abundant as that species; fishing hut above Dutch Gap Canal; Fredericksburg; 72d mile-post, near Brooke.

This plant has the same general character as T. Meekiana, but is more slender than that and has the pinnules and pinnm less crowded. Asnbsp;these features appear to be constant, this form seems entitled to be considerednbsp;as a variety.

Frond tripinnate, arborescent; pinna3 and pinnules opposite; lower penultimate pinnae without pinnules or pinnae near tlie insertion on thenbsp;main rachis; leaf-substance of the pinnules thick and leathery; pinnae ofnbsp;the lower portion of the compound pinnae passing towards the summit ofnbsp;the compound pinnae into crenately toothed and finally into entire pinnules; lower and basal pinnules crenately toothed, oblong to subquadratenbsp;in form, separate to the much narrowed base; upper pinnules entire, elliptical to subrhombic, slightly decurrent, united more and more in ascending; nerves of the crenately toothed pinnules composed of a midnervenbsp;which dissolves into branches towards its summit, sending off verynbsp;obliquely and alternately on each side nerve-bundles curving stronglynbsp;outwards to enter the teeth, and several times subdivided, in the uppernbsp;entire pinnules composed of a midnerve sending off obliquely and alternately lateral branches curved outwards and forked one or more times,nbsp;or simple towards the tips of the pinnules; all lateral nerves strong.

This fine plant seems to have no near affinity with any described fossil. The rachises are strong, rounded, and jirominent.

Plate XXXIX, Fig. 4; Plate XL, Fig. 1; Plate XLI, Fig. 6; Plate XLII, Pigs. 1, 2, 4; Plate XLIII,

Frond tripinnate, very large, arborescent; leaf-substance of the pinnules thick and coriaceous; rachises strongly winged, sometimes a little flexuous; pinnm of the first order very long and spreading; ultimatenbsp;pinnm in the lower part of the frond very remote, subopposite to alternate; pinnules quite variable, according to position on the frond and compound pinnaj, and always rather remotely and very obliquely placed,nbsp;alternate to opposite, and decurrent; in the lower part of the frond as innbsp;PI. XXXIX, Fig. 4, and PI. XL, Fig. 1; oblong-lanceolate to narrowlynbsp;elliptical, acute, cut more or less deeply in the basal pinnules and verynbsp;obliquely into oblong or ovate acute lobes, those towards the tips of the

ultimate pinnae becoming entire and narrowly elliptical. In tliis portion of the frond there is a distinct midnerve in each pinnule, which at its summitnbsp;splits into branches, while it sends off alternately and obliquely on eachnbsp;side lateral nerves into the lobes. These in the basal lobes have a midnerve which sends off alternately on each side simple nerves, and in thosenbsp;up higher they fork once or twice; pinnules of the middle portion of thenbsp;frond and compound pinnae (see PI. XLII, Fig. 2) are remote, linear, acute,nbsp;and decurrent to form a wing, cut into acute sliort teeth; midnerve andnbsp;lateral nerves of these rather slender but distinct; lateral nerves of eachnbsp;tooth forking deeply, one branch ending in the tip of the teeth; pinnules ofnbsp;the upper part of the frond and compound pinnae (see PI. XLII, Figs. 1,nbsp;4) reduced to narrowly oblong lobes and teeth. The ultimate pinnae also,nbsp;in passing to the upper portions or tips of the compound pinnae, pass intonbsp;lobed and tootlied pinnules similar to those down lower. The compoundnbsp;pinnae most probably end abruptly with a terminal pinnule like thosenbsp;lower down. (See PI. XLIII, Fig. 1.)

Localities: Fredericksburg; road-side near Potomac Run; rather abundant at the former place, rare at the latter.

The variability of this splendid plant causes it in one or another of its forms to approach several that are described under other names. Itnbsp;belongs to the S])henopteris Mantelli type of Thyisopteris, but the thicknbsp;leaf-substance, I�emoteness of the pinna? and pinnules, the strong wing,nbsp;and the once forking lateral nerves distinguish it. In PI. XLIII, Fig. 1,nbsp;the tip of a compound pinna is shown, and it has abruptly terminating itnbsp;a pinnule similar to those lower down. It is a good deal like T. insignis,nbsp;var. angtistipennis, as shown in PI. XLIII, Fig. 3, but this latter does notnbsp;have the rachises winged. Among described fossils we find Aspidiumnbsp;Johnstrupi, Ileer,^ something like the plant now in question.

Frond bipinnate or tripinnate, arborescent; rachises stout and prominent ; leaf-substance thick and leathery; ultimate pinnm alternate ; pinnules

alternate, linear, acute, narrowed to a long, slender, wedge-shaped base, and attached by the midnerve alone; pinnules cut more or less deeply andnbsp;obliquely into oblong or narrowly ovate, acute, diverging teeth; midnervenbsp;slender; lateral nerves simple, one in each lobe or tooth, slender.

This plant belongs to the Splienopteris Mantelli type, and is strikingly like T. insignis. The rachis, however, is not winged, and the pinnules arenbsp;narrowed to a longer and more slender base. This plant is not uncommonnbsp;at Fredericksburg, and is sometimes found with pinnules even more slendernbsp;than those depicted. They cover with a confused heap some fragments ofnbsp;the rock.

Frond tripinnate, arborescent; leaf-substance thick and coriaceous; principal rachis strong, keeled on the under side; pinnae of ultimate ordernbsp;alternate, short, linear-lanceolate, acute; pinnules crowded, obliquelynbsp;placed, short, subacute to obtuse, much narrowed at base, and decurrentnbsp;in the basal ones to form a partial wing, those higher up united more andnbsp;more, and passing through entire pinnules into more or less united lobes:nbsp;lower or basal pinnules cut very obliquely more or less deeply into subacute to obtuse teeth; nerves very slender and seen with diflficnlty, composed in the pinnules of a midnerve which sends off obliquely and alternately into the teeth lateral nerves, which are once or twice forked andnbsp;curve outward.

This plant is near Thyrsopteris insignis, but the pinnules do not form a continuous wing, and they are, as a rule, shorter and broader than thosenbsp;of the latter. The pinnules are more crowded, and the nerves differ much.nbsp;This plant has some resemblance to the Wealden fossil Sphempterisnbsp;Gocpperti Dunker.

Frond bipinnate or tripinnate; racliises all slender; ultimate pinnae opposite or subopposite, short, subacute; penultimate pinnae very long;nbsp;upper basal pinnule of the ultimate pinnae heteromorphous, much largernbsp;than the others, cut more or less deeply into three obtuse lobes or teeth;nbsp;pinnules mostly elliptical or subrhombic, lower ones separate to the base,nbsp;upper ones more and more united and passing into ovate lobes; leaf-substance thick'; nerves very strong, standing out like threads; midnervenbsp;of the pinnules splitting up into branches at the summit, sending off alternately on each side lateral nerves which branch once or twice, and in thenbsp;lobes of the heteromorphous pinnule sending olf a flabellately divergingnbsp;nerve-bundle, the branches of which mostly fork near their ends.

This belongs to the Sphenopteris type of Thyrsopteris, and resembles in some respects several of that type, but. it is distinguished by its strongnbsp;nerves and heteromorphous upper basal pinnule.

Frond tripinnate, arborescent, of large size?; principal rachis somewhat flexuous; rachises of all orders winged; pinnules decurrent, rather remote, varying in shape according to position and consequent lobingnbsp;from oblong to linear-acute, diminishing much in size and depth of lobingnbsp;in ascending towards the summits of the compound pinnm, much narrowednbsp;at base and going off obliquely; the lower pinnules deeply and obliquelynbsp;cut into narrow, oblong, obtuse lobes, upper ones narrowly oblong tonbsp;linear, with acute, elliptical, shallow teeth; nerves in each lobe or toothnbsp;distinct, in those of the lower parts of the pinnae deeply forked, in thosenbsp;of the upper parts simple, all very oblique and approximately parallel.

Localities: Red clay ball in banks of Dutch Gap Canal; Fredericksburg; 72d mile-post, near Brooke; hill-side near Potomac Run; fishing-hut above Dutch Gap Canal; in all places rather rare.

This is one of the most widely diffused of the Potomac ferns. In that respect it differs from most of the ferns of this formation, for they arenbsp;usually much isolated in occurrence. It does not seem to be nearly alliednbsp;to any known fossil.

Plate XLIV, Fig. 4; Plate XLV, Fig. 3; Plate XLVIII, Fig. 2; Plate XLIX, Figs. 3, 4; Plate LV,

Frond tripinnate, arborescent; pinnules and lobes narrowly oblong to acute; pinnae and pinnules usually much crowded; ultimate pipnae andnbsp;pinnules alternate, diminishing in passing towards the ends of the compound pinnae into pinnules and lobes ; pinnules and lobes narrow, obliquelynbsp;cut, in shape narrowly oblong to linear, lower pinnules separate to base,nbsp;and furnished with narrowly elliptical acute lobes and acute teeth, passingnbsp;in ascending into more and more fully united narrowly elliptical teeth;nbsp;nerves in each lobe of the upper pinnules forked, with the upper branchnbsp;forking again or single in some cases. In the lower pinnules the lobes havenbsp;a midrib with alternate simple branches going off on each side ; midrib andnbsp;lateral nerves of the pinnules all slender.

Localities: Entrance to Trent�s Reach; fishing-hut above Dutch Gap Canal; 72d mile-post, near Brooke; hill-side near Potomac Run; notnbsp;common anywhere.

This is a widely diffused fern. It is distinguished by the narrowness of its lobes and pinnules and the absence of a wing on the rachises. Itnbsp;belongs to the Splienopteris Gcepperti type of Thjrsopteris. Some of thenbsp;specimens sent from Professor Uhler�s collection, gotten at Baltimore, tonbsp;New Orleans, and thus lost, were similar to this plant, and hence itnbsp;probably occurs at Baltimore.

Frond tripinnate, large, arborescent; principal rachis strong; penultimate pinnte alternate, with strong rigid rachises comparatively short, terminated abruptly by an ultimate pinna similar to those lower down on the

compound pinna; ultimate pinnae of the upper part of the frond (see Fig. 2) reduced to acute, elongate, elliptical lobes and teeth; the ultimate pinnaenbsp;subopposite to alternate, obliquely placed, linear-lanceolate, subacute, withnbsp;slender midribs terminated by an elliptical subacute lobe, attached to thenbsp;principal rachis by a much narrowed base, composed of the midnerve withnbsp;a narrow wing; pinnules small, linear-oblong to elongate-elliptical, acutenbsp;to obtuse, basal ones separate nearly to the midnerve, those of the ultimatenbsp;pinnae slightly notched into acute teeth; pinnules towards the tip of thenbsp;ultimate pinnae and higher on the frond without the teeth and more unitednbsp;at base; nerves in the basal pinnules composed each of a slender midnerve,nbsp;which sends off on each side alternate simple nerves which go one to eachnbsp;tooth ; in the lobes and simple pinnules higher on the frond, the nerves oncenbsp;or twice forked or simple; usually the second forking occurs in the uppernbsp;branch of the forking nerves and is found in the lower pinnules of the frondnbsp;on the ultimate pinnae.

This fine plant belongs to the Sphenopteris Mantelli type of Thyrsop-teris, and is in some of its forms like T. rarinervis and T. angiistifolia. It is not winged, however. All the specimens figured except the small onenbsp;(Fig. 5) come from Fredericksbui-g.

Frond tripinnate, large, arborescent; pinnae and pinnules usually crowded; racbises very stout, round, and prominent; ultimate pinnae opposite to alternate, lanceolate in outline, rather short; pinnules passingnbsp;rapidly into lobes and teeth towards the upper part of the frond andnbsp;compound pinnae; lower pinnules narrowed to the base, oblong or sub-quadrate, acute, cut more or less deeply and very obliquely into narrowlynbsp;elliptic acute teeth. In the upper parts the pinnules become narrowlynbsp;elliptic, toothed, and united by decurrent bases, or pass into very obliquelynbsp;placed teeth of the same shape. The ultimate pinnas pass into pinnules

in the upper part of the compound pinnae. The nerves are fine but distinct, closely placed, deeply forked, flabellately diverging in each lobe and tooth, consisting of a slender inidnerve, which sends off very obliquelynbsp;deeply forked or simple branches.

Localities: Fredericksburg; road-side near Potomac Run; near Telegraph Station; fishing-hut above Dutch Gap Canal; rare everywhere.

This fine plant belongs to the Sphenopteris longifoUa type of Wealdeii ferns. Its facies is one highly characteristic of the Potomac ferns, including more forms than any other. It is not closely allied to any describednbsp;fossil known to me.

Plate XXIV, Pig. 3; Plate XLVI, Pig. 1; Plate L, Pigs. 6, 9; Plate LI, Figs. 4, 6, 7; Plate HV, Fig.

6; Plate LV, Pig. 4; Plate LVl, Pigs. 6, 7 ; Plato LVII, Pig. 6; Plate LVIII, Pig. 2.

Frond quadripinnate, large, spreading, and arborescent; rachises strongly winged, keeled on the under side; principal rachis very stout, andnbsp;often more or less flexiioiis; leaf-subtance of the pinnules thick; arrangement of the ultimate pinme various. The plant shows a tendency to a palmate mode of subdivision of the principal rachis (see PI. LVI, Fig. 6);nbsp;compound pinnae abruptly terminated by penultimate pinnae like thosenbsp;down lower (see PI. LI, Fig. 6); ultimate pinnae crowded, quite short;nbsp;lower pinnules of the ultimate pinnae, in the lower part of the frond cutnbsp;more or less deeply and obliquely into narrowly oblong to ellipticalnbsp;obtuse lobes or rounded teeth, separate to the wing of the rachis, obliquelynbsp;placed, much narrowed at the base, elliptical or ovate in shape ; pinnulesnbsp;in ascending towards the summit of the frond and ends of the compoundnbsp;pinnae pass into entire elliptical pinnules, and these, united more and more,nbsp;pass into lobes and teeth; midnerve of the lobed pinnules splitting at thenbsp;summit and sending off down lower alternately into the lobes branchesnbsp;which fork once or twice ; branches in the upper pinnules either oncenbsp;forked or .simple.

Localities: Fredericksburg, not uncommon; red clay ball in banks of Dutch Gap Canal; rare.

Frond tripinnate, large, arborescent; rachises strong, narrowly winged; pinnae and pinnules very remotely placed; penultimate pinme subopposite,nbsp;with ultimate pinnae abruptly and irregularly diminished in length andnbsp;size; ultimate pinnae linear-lanceolate, passing above into lobed, toothed,nbsp;or entire pinnules; basal pinnules of the lowermost ultimate pinnae narrowly oblong, acute, denticulate, passing towards the tips of the ultimatenbsp;pinnae rapidly into narrowly oblong, acute lobes and teeth; nerves in thenbsp;pinnules and lobes, composed of a midnerve which sends off obliquelynbsp;and alternately on each side branches, which are forked in the lower ones,nbsp;simple above, fine, closely placed, but distinct.

This plant belongs to the Sphenopteris Gcepperti type. The principal rachis is very strong. It is probable that in this and all the specimens ofnbsp;Thyrsopteris, CladopMebis, Pecopteris, etc., the principal rachises are portionsnbsp;simply of compound pinnae. In the descriptions, when plants are given asnbsp;bipinnate, tripinnate, etc., it is meant that the frond is probably at leastnbsp;divided to the extent named. This plant seems to be not very near anynbsp;other described fossil.

Frond tripinnate; rachises distinctly winged; pinnules and lobes, especially the latter, very narrow; penultimate pinnae alternate, rapidlynbsp;diminished in ascending towards the summit of the compound pinnae intonbsp;ultimate pinnae and pinnules, and finally into lobes; ultimate pinnae subopposite, closely placed, decurrent to form a wing, the lower ones cutnbsp;obliquely and more or less deeply into narrowly oblong or ellipticalnbsp;pinnules towards their bases, but towards their' ends these pass into lobesnbsp;and teeth of the same form, narrowed to a subpetiolate base; higher onnbsp;the compound pinna they change rapidly through toothed pinnules into

entire ones, and finally into lobes and teeth; nerves in the pinnules and lobes, forked deeply in the basal ones, in the upper ones simple, all verynbsp;oblique, fine, but distinct.

Localities: Fredericksburg; fishing-hut above Dutch Gap Canal; entrance to Trent�s Reach; White House Bluff.

This plant is quite widely diffused. It is comparatively abundant at White House Bluff, where a number of poorly preserved specimens occur,nbsp;evidently in some cases being fragments of large portions of the frond.nbsp;It is also not very rare at the entrance to Trent�s Reach. In other placesnbsp;it is very uncommon. The general aspect of this plant is much like thatnbsp;of Thyrsopteris angustifolia, but the distinctly winged rachis compels me tonbsp;separate them. It belongs to the Sphenopteris Mantelli type.

Frond and pinnae unknown ; ultimate pinnae terminated by a broadly fan-shaped pinnule, which is toothed on the terminal margin; pinnules notnbsp;fully shown, only those near the tip of the ultimate pinnae seen, alternate,nbsp;elliptical, acute, furnished with ovate teeth; leaf-substance thick; nervesnbsp;not seen.

Only one small specimen was found, but the plant seems to be a distinct new species, not near to any described fossil.

Rachis of the penultimate pinnae stout; ultimate pinnae closely placed, opposite or subopposite, sliort, linear-acute; pinnules minute, passing tonbsp;lobes towards the ends of the ultimate pinnae, subrhombic to ovate, decurrent to form a wing, lower ones slightly toothed; leaf-substance thick;nbsp;nerves in the pinnules composed of a midnerve, which goes ofiP obliquelynbsp;and is turned strongly outward, and sends off alternately on each sidenbsp;branches which are forked or simple.

This, although found only in one or two small fragments, seems to be quite a distinct new species. It looks more like some of the Gleicheniwnbsp;from the Lower Cretaceous of Greenland than any other plant.

Frond tripinnatifid, arborescent; rachises slender; ultimate pinnm alternate; primary pinnrn towards the summit suddenly changing fromnbsp;penultimate pinme toTiltimate ones (see PI. LVII, Fig. 7); ultimate pinnmnbsp;short, closely placed, terminating in acute oval lobes, obliquely inserted,nbsp;alternate, changing in passing to the summits of the principal pinnm and ofnbsp;the penultimate ones into lobed pinnules and finally into entire pinnules,nbsp;much narrowed at base, and attached by the narrowly winged midnerve,nbsp;cut down nearly fo the midnerve in their basal portions into narrowlynbsp;oblong or elliptic-acute pinnules; towards their ends and higher on thenbsp;compound pinnm the pinnules graduate into lobes and teeth; pinnules andnbsp;lobes minute; nerves in the pinnules of the lower parts forked deeply,nbsp;with the upper branch forking again; in the lobes higher simply forked.

This elegant little plant is not very rare at Fredericksburg. It is noteworthy for the very regular and elegant shape of the pinnules andnbsp;lobes and for their minute size.

Frond apparently palmately branching, with the primary pinnae radiating from the top of the common stipe; ultimate piiinm of the central compound pinnae passing abruptly in ascending into obtusely lobed pinnules,nbsp;and at the top changing into entire elliptical pinnules; ultimate pinnaenbsp;closely crowded, short, and obliquely inserted, passing in ascending intonbsp;lobed and finally into entire pinnules, those of the upper side of the penultimate pinnae larger and more deeply cut than those of the lower side, thosenbsp;towards the base of the penultimate pinnae cut into elliptical subacutenbsp;pinnules and lobes, which are narrowed at base and obliquely placed, thenbsp;pinnules of the upper side being sometimes crenately toothed; leaf-sub-

stance leathery and thick; nerves very strong, causing the leaflets sometimes to look as if they were corded. In the crenate pinnules (Fig. I'*) the nerves consist of a midnerve which splits up towards the summit and sendsnbsp;off at base two nerve-bundles ; these diverge flabellately into the teeth, withnbsp;the branches simple and forked; higher the lateral nerves fork deepljynbsp;with the upper branch forking again; the entire pinnules (Fig. P) havenbsp;branches diverging alternately from a midnerve, curving outward and oncenbsp;or twice forked.

Tliis plant belongs to the Sphenopteris Gcepperti type. It seems to be a well-characterized new species of a strongly defined Wealden type.

Plate LIT, Figs. 2-4; Plate LIII, Figs. 1-3; Plate LIV, Fig. 10; Plate LVII, Fig. 2.

Frond tripinnate or qiiadripinnate, large and spreading; leaf-substance thick and leathery; rachises of the penultimate pinnse often partially ornbsp;fully winged; ultimate pinnae varying in size and shape with their position on the frond, tending to pass in ascending towards the ends of thenbsp;penultimate pinnae rapidly through lobed into entire pinnules. Principalnbsp;rachis generally stout and prominent, often flexuous; ultimate piniue onnbsp;the upper side of the penultimate pinna sometimes much larger than thosenbsp;on the lower side, especially the basal upper one; ultimate pinnai of thenbsp;lower part of tlie frond and compound pinnae furnished with remote, elliptical, oblong, or subrhombic pinnules, which pass in ascending into lobesnbsp;and teeth of the same nature. In the pinnules of the lowest portions thenbsp;nerves are composed of a midnerve which sends off flabellately divergingnbsp;branches, which are forked or simple; in the lobes and teeth of the uppernbsp;portions they consist of a midnerve which branches- several times, beginning near the base, the branches diverging flabellately, or of a lateral nervenbsp;in each lobe which forks once or twice.

A number of good specimens of this plant were obtained. I have, with a good deal of hesitation, united under this species a number of formsnbsp;which differ somewhat in aspect, but there seems to be such a transition

from one to the other as to forbid their separation. Plate LIT, Fig. 2, shows no wing on the rachis of the ultimate pinna, but shows a featurenbsp;common in this species, viz: the ultimate piniim on the upper side of thenbsp;penultimate rachis are larger than those on the lower side. In Fig. 3, ofnbsp;the same plate, the rachis is not winged, and the ultimate pinnae do notnbsp;sliow the marked disparity in size often seen ; Fig. F, of the same plate,nbsp;shows the ultimate pinnm or pinnules decurrent, and forming a partialnbsp;wing to the rachis. The nerves in the lobes or pinnules of this form arenbsp;more mxmerous and deeply forked than in Fig. 2. In PI. LIII, Fig. 1, thenbsp;penultimate rachis is winged, and the pinnules, here reduced to lobes,nbsp;have remote, sparingly branched, strong nerves. The ultimate pinnae donbsp;not differ much in size. In Fig. 2, of the same plate, we have a surprisingnbsp;difference in the size of the ultimate pinnae on opposite sides of the penultimate rachis. In Fig. 3, of this plate, the usual disparity of the ultimatenbsp;pinnae is seen, and the pinnules differ from the normal ones markedlynbsp;in the nerves, which are fine, closely placed, deeply forked, and comparatively numerous. In PI. LIV, Fig. 10, the basal upper pinnule isnbsp;decidedly longer than the rest, and directed upwards parallel with thenbsp;penultimate rachis, which is strongly winged. This is probably the uppernbsp;portion of a compound pinna. This fern seems to be not closely allied tonbsp;any described fossil, and to have been a large plant.

Frond apparently palmately divided; plant slender; principal rachises slender, rounded, and prominent; ultimate pinnge short, distant, opposite,nbsp;pinnules remote; leaf-substance thick, upper basal pinnule larger than thenbsp;rest, more copiously and deeply lobed; pinnules subrhombic to rhombic innbsp;shape, slightly curved forward, acute, rarely obtuse; nerves very distinct,nbsp;composed in the pinnules of a midnerve which sends off alternately andnbsp;very obliquely on each side forked or simple nerves, and which at its summit dissolves into branches. In the heteromorphous basal upper pinnule anbsp;nerve-bundle goes off flabellately diverging into the basal lobes, thenbsp;branches of which are simple.

Plate LIV, Fig. 1, depicting a specimen from the last-mentioned locality, differs from the more common Fredericksburg forms in having the penultimate rachis keeled, perhaps because the under side is shown. Itnbsp;gives the summit of a primary pinna.

Frond tripinnate; rachises strongly winged; principal rachis flex-uous; penultimate pinnae alternate, with a strong rigid rachis; ultimate pinnae alternate, short, attached by the narrowly winged rachis which forms a sort of petiole, cut obliquely into oblong, obtuse, or spatulate pinnules ornbsp;lobes to varying depth, according to the position on the pinnm; uppernbsp;basal pinnules always larger than the lower pinnules, furnished with threenbsp;shallow, very obtuse lobes; towards the summit of the ultimate pinnae andnbsp;of the frond the pinnules pass to obtuse lobes; nerves in each pinnule andnbsp;lobe fine, closely placed, flabellately diverging, with simple or forkingnbsp;branches.

This seems to be a very distinct new species, and it is very rare. It is somewhat like T. varians.

Plate LIII, Fig. 5; Plate LV, Figs. 6, 7; Plate LVI, Figs. 2, 5; Plate LVII, Figs. 1, 5; Plate LVIII,

Frond quadripinnate, spreading, arborescent ? ; rachises comparatively very slender; primary rachis somewhat flexuous; penultimate pinngenbsp;alternate or opposite, long, closely placed, passing towards the summit ofnbsp;the principal pinnae into ultimate pinnae; ultimate pinnae short, oppositenbsp;to alternate, terminating in a three-lobed segment, usually closely placed,nbsp;oblong-lanceolate in form, passing above into lobed and simple pinnules;nbsp;pinnules passing in ascending into simple ones, and finally into lobes.

lower ones cut obliquely into oblong or elliptical lobes or teeth, basal ones sometimes blunt-lobed, greatly narrowed at base, all minute ; leaf-substancenbsp;thin; nerves in the lobes or teeth slender but distinct, composed in thenbsp;pinnules of a midnerve with obliquely placed, alternate forking or simplenbsp;branches on each side, and in the lobes and teeth of lateral nerves,' whichnbsp;fork once or twice and go off very obliquely.

Localities: Fredericksburg; entrance to Trent�s Reach ; White House Bluff; fishing-hut above Dutch Gap Canal; rare.

This elegant little plant is one of the more widely diffused ferns. It is noteworthy for the minuteness of the pinnules and lobes. It seems tonbsp;be a well-marked new species.

Frond arborescent, tripinnate; principal rachis proportionally very stout, rigid, and prominent; penultimate pinnae alternate, closely placed,nbsp;much narrowed at the base, decurrent; lower pinnules of the ultimatenbsp;pinnae elliptical, narrowed at base, slightly and obtusely toothed, minute,nbsp;the upper basal pinnule larger than the rest and more deeply toothed;nbsp;pinnules on the upper side generally larger than those on the lower, andnbsp;showing a toothing iip higher towards the tips of the ultimate pinnae;nbsp;pinnules towards the ends of the ultimate pinnae passing into lobes andnbsp;teeth; leaf-substance rather thick; nerves in the lower pinnules pinnatenbsp;from a midnerve, with branches forked and simple, those of the lobes upnbsp;higher forked or simple.

This is a plant with very minute pinnules and lobes, which has the penultimate rachises not winged, and which thus differs from the varietynbsp;alata.

This differs from T. microloha mainly in the presence of a wing on the rachises of the penultimate pinnm, the smaller size of the principal

racliis, and in the proportionally larger size of the pinnules and lobes. PI. LV, Fig. 5, appears to represent the upper portion of a compoundnbsp;pinna, corresponding to the upper portion of the fragment represented innbsp;PI. LVII, Fig. 4, where the pinnules are reduced to lobes and the ultimatenbsp;pinnae to pinnules.

The plant is not common anywhere, but is most abundant in thin shale partings in the bank a little above the spot at the fishing-hut, wherenbsp;so many plants were collected. It does not occur, strange to say, at thisnbsp;last-named spot, which is only a few yards distant. The fine specimen,nbsp;PI. LV, Fig. 5, was found at the Dutch Gap locality.

Frond very small, tripinnate; rachises slender; ultimate lower pinnm or pinnules very minute, .short, rather remotely placed, much narrowed atnbsp;the base, subrhombic in shape, cut very obliquely nearly to the midnervenbsp;into very small elliptical or oblong pinnules or lobes, which are mostlynbsp;obtusely rounded at tlie ends, rarely subacute, the lower ones divergingnbsp;considerably; the ultimate pinnae terminate in a three-lobed segment; thenbsp;ultimate pinnae pass towards the ends of the penultimate pinnae and ofnbsp;the principal pinnae into pinnules, which have a wedge-shaped base, andnbsp;are cut deeply into three lobes, the lower pair diverging strongly; nervesnbsp;of the pinnules and lobes fine but distinct, closely placed, tliose of thenbsp;pinnnles in the lower portion of the pinnae flabellately diverging from anbsp;short basal nerve, mostly simple in the lobes, once or twice forking, andnbsp;without the basal nerve.

Thi s is a very small plant, which seems quite distinct from all other described fossils.

Frond tripinnatifid; rachises slender; idtimate pinnae opposite or subopposite, of unequal length on opposite sides of the penultimate rachis, rather remote, graduating above through lobed and dentate into entire pinnules, the latter being at the summit of the compound rachis and becomingnbsp;more remote in the upper part; pinnules opposite, elliptical, much narrowednbsp;at the base, passing towards the summit of the ultimate and primarynbsp;pinnae into entire ones, the lower ones cut into shallow, elliptical, subacutenbsp;teeth; nerves fine, in the pinnules composed of a midnerve which in thenbsp;toothed lower pinnules sends oft� very obliquely and alternately flabellatenbsp;nerve-bundles with forking or simple branches, and splits up into branchesnbsp;at its summit; in the entire pinnules it gives otf in like manner lateralnbsp;nerves that are forked or simple.

The marked inequality in the length of the ultimate pinnae on opposite sides of the principal rachis is the most noteworthy feature of this smallnbsp;plant. It seems to be unique.

Frond probably tripinnate; rachises slender; penultimate pinnae alternate, short, closely placed, terminating in a three-lobed segment, with broadly winged rachis; pinnules remote, those on the upper side largernbsp;and less obliquely placed than those on the lower side, much narrowed atnbsp;base, and decurrent to form a broad wing, cut more or less deeply intonbsp;ovate teeth, elliptical to subrhombic in shape; leaf-substance thick; nervesnbsp;distinct, pinnately departing from a slender midnerve, simple, one in eachnbsp;tooth.

Although only a small fragment was found, this plant seems to be a distinct species. It is much like Tliyrsopteris Maaldana^ Heer.

' Compare Flor. Foss. Arc., vol. 4, Part II, Beitriige zur Jnra Flor., etc., PI. 1, Fig. 1�.

Frond tripinnatifid; pinnae of ultimate order and pinnules subopposite, remotely placed, short; pinnules narrowly oblong, obtuse, passing abovenbsp;into entire ones, lower ones cut to varying depths into oblong, very obtusenbsp;lobes; lateral nerves very strong, in the lower lobes given off pinnatelynbsp;on each side of a midnerve which splits up at the summit; the lateralnbsp;nerves forked or simple, in the upper lobes flabellate and forking once ornbsp;twice.

Localities: Red clay ball in the banks of Dutch Gap Canal; hill-side near Potomac Run ; i-are.

This plant has the facies of a Cladophlebis. It seems to be a distinct new species.

Frond bipinnate or tripinnate ; ultimate pinnie winged; leaf-substance thick; pinnules small, much narrowed at base, almost petioled, distant,nbsp;elliptical or subrhombic in shape, acute; lower ones cut into divergingnbsp;ovate-acute lobes, upper ones entire; nerves strong, composed in each pinnule of a midnerve which splits up towards the summit and sends off pinnately into the lobes and teeth lateral nerves which fork usually once.

Frond tripinnatifid; primary rachis stout, somewhat flexuous; ultimate pinnm alternate, winged, closely placed; pinnules crowded, much narrowed at base, short' in outline, triangular, cut more or less deeply intonbsp;lobes which spread widely from the midnerve, standing almost at rightnbsp;angles with it, the lobes more or less club-shaped or spatulate in form, thenbsp;basal ones being obtusely three-lobed; the pinnules are broadest at base,nbsp;and stand nearly at right angles witli the midrib ; nerves strong, com-

posed m the lower lobes of a flabellately diverging nerve-bnndle, the branches of which are forked or simple; in the upper ones composed ofnbsp;forking nerves.

Frond tripinnate, arborescent; principal rachis stout; ultimate pinnm alternate, lineardanceolate in outline, terminating in an acute lobed segment ; pinnules closely placed, alternate, oblong or subrhombic, acute,nbsp;passing above into united lobes, cut more or less deeply into subrhombicnbsp;lobes, much narrowed at base, decurrent to form a wing on the penultimatenbsp;rachis; nerves of the pinnules composed of a midnerve which splits up atnbsp;the top and sends off pinnately into the lower lobes nerve-bundles whichnbsp;diverge flabellately in the lobes, the branches being simple, or forked innbsp;the lower lobes ; in the upper lobes the lateral nerves fork once or twice.

The penultimate pinnm of this plant in the upper parts of the compound pinnae are reduced to pinnules, as is shown in PI. LX, Fig. 8, and in the lower portions of the frond, as in PI. LIX, Fig. 6, they seem to passnbsp;into iiltimate pinnae. These do not have the rachis to which they arenbsp;attached winged. The plant seems to be a distinct new species.

Frond tripinnate; principal rachis stout; pinnae alternate; ultimate pinnae short, lanceolate in shape, rachis winged, terminating in a lobednbsp;segment formed of united and reduced pinnules; pinnules towards the endsnbsp;of the ultimate pinnae passing into lobes and teeth; those of the lower portion of the ultimate pinnae much narrowed at base, united by decurrencenbsp;to form a wing, oblong, terminating in three acute teeth, cut into retuse

lobes; lateral nerves of the pinnules few and remote, going pinnately on each side of the midrib into the lobes, and forking once or twice, allnbsp;strong.

This small plant reminds one of Thyrsopteris squarrosa, but appears to be a well-marked distinct species, not nearly allied to any described fossil.

Small, circinate fern fronds, similar to the form depicted in Fig. 5, are quite common in the shale on the hill-side near Potomac Run. Theynbsp;occur mostly in the form of small fragments. This locality is noteworthynbsp;for the great number of specimens of a comparatively small number ofnbsp;species of ferns that it affords. It is eminently a fern locality, being thenbsp;only place where the specimens of that family surpass in numbers allnbsp;others put together.

The genus Osmimda is not represented in the Potomac by many species, but the number of individuals, of at least one of the species, is considerable.

Frond most probably bipinnatifid, spreading; rachises slender; sterile and fertile pinnules on the same pinna; lower pinnules of the ultimatenbsp;pinnse fertile, the upper ones sterile, occasionally some of the basal lobesnbsp;of the upper pinnules fructified; pinnules alternate, remote, especially thenbsp;fertile ones; fertile pinnules much reduced- in size, oblong in form, withnbsp;bluntly rounded lobes, which are covered with sori; sterile pinnules short,nbsp;cut more or less deeply into oblong, elliptical, subacute lobes, obliquelynbsp;placed, narrowed at base to a sort of petiole; nerves fine, but distinct,nbsp;branching flabellately in each lobe or tooth, departing from a more or lessnbsp;pronounced midnerve, the branches sometimes forked, but more commonlynbsp;simple.

This is a well marked species. Its rarity may be only apparent. The plants found in the red clay ball form a peculiar assemblage, a number ofnbsp;them, as in this case, being found nowhere else. The amount of materialnbsp;in this ball was small, and owing to this, we can not say whether or notnbsp;the plants found in it were actually rare in the stratuix represented by thisnbsp;ball, and from which it was torn. It would seem that this ball belonged tonbsp;a fossiliferous layer, not now to be seen in place in the exposures aboutnbsp;Dutch Gap. No doubt many originally rich fossiliferous layers have beennbsp;destroyed in the local erosions to which the formation was from time tonbsp;time in the course of its deposition subjected.

The plant is possibly composite in nature, and not a sharply differentiated Osmunda, but as it contains more of the features of this genus than any other, I have placed it there. The sori are very small, being fine dots.nbsp;The exact details of their structure could not be made out.

Plate XLI, Pig. 5; Plate LVIII, Fig. 9; Plate LIX, Figs. 1, 4, 8, 9, 11; Plate LX, Pigs. 2, 4, 5, 9;

Sterile frond large, arborescent, tripinnate; rachises stout, especially the principal ones; ultimate pinnse subopposite to alternate, closely placed,nbsp;linear-lanceolate, acute, ending with pinnules reduced to united teeth andnbsp;passing towards the summits of the compound pinnse into pinnules; pinnules or reduced pinnse alternate, closely placed, oblong to ovate, passingnbsp;above towards the tips of the compound and ultimate pinnse through oblongnbsp;or ovate lobed or toothed pinnules into entire ones, and finally into unitednbsp;teeth, ovate-acute in form. The lower pinnules or reduced pinnse are muchnbsp;narrowed at base, cut more or less deeply into ovate, elliptical, subquadrate, acute lobes and teeth, the lobes, especially the basal ones, being oftennbsp;toothed; the nerves in each lobe composed of a midnerve sending offnbsp;obliquely and alternately branches either forked or simple; reduced in thenbsp;teeth of the upper pinnules and of the terminal portions of the lower onesnbsp;to forked or simple lateral nerves in each lobe or tooth; the fertile frondnbsp;distinct from the sterile one; the pinnules of the former much reduced in

size, very thick and leathery, apparently consisting of a midrib, which has on each side a narrow thickened lamina, bearing on the margins large fruit-masses rounded in form.

The fertile forms are very rare at this locality, but the sterile ones are very abundant, and much the most common of the specimens found here.nbsp;The form depicted in PI. LX, Fig. 5, I regard as the fructified form of thenbsp;fern -^liich is described above, and which shows so many well-preservednbsp;sterile specimens. As, however, the sterile and the fructified forms werenbsp;not found connected together, the union can not be taken as certainlynbsp;authorized. Unfortixnately the fructification is not well enough preservednbsp;to render its details clear. Fig. 5 gives the appearance as seen in naturalnbsp;size with the unaided eye. Fig. 5'^ gives the appearance under a lens.nbsp;The apparent fruit-masses look like rounded masses of naked sori ornbsp;sporangia. The entire fructified pinnules are so much thickened and sonbsp;poorly preserved, that nothing but the rounded shape and granular appearance of the fruit-masses can be made out. Each mass of fruit seems tonbsp;represent a contracted and modified pinnule or lobe. The metamorphosisnbsp;of the pinnules reminds one of Osmunda more than of any other livingnbsp;genus, and I place the plant provisionally in this genus. Possibly thisnbsp;may be a new genus, composite in character, which has some of thenbsp;features of Thyrsopteris and Osmunda, for there is an indication of a cupshaped grouping in the fruit dots. It is strange that no specimen of thisnbsp;plant was found on the road-side near by.

Frond tripinnatifid, large, arborescent; rachises proportionally slender; pinnae and pinnules alternate; rachises of the ultimate pinnae narrowlynbsp;winged; pinnules with membranaceous leaf-substance, short, oblong innbsp;shape, and acute, attached by the middle point of the narrowed base, cutnbsp;more or less deeply into rounded, subquadrate, or broadly oval lobes, thenbsp;lower ones of which have shallow, subacute teeth; fructified form notnbsp;seen. Nerves in each lobe remote, strong, composed of a nerve-bundle

which diverges flahellately from a more or less pronounced midnerve, the branches usually once forked, rarely bifurcate.

This plant is much more rare than the type species, and, although evidently nearly allied to it, has the nerves more widely diverging andnbsp;remote, a more regular dentation, a winged rachis in tiie ultimate pinnae,nbsp;and wider, more rounded lobes. The pinnules also are decidedly broadernbsp;in proportion to their length.

The Jurassic genus Sagenopteris is represented in the Potoma�c flora by several well-characterized species. None of these, however, seem tonbsp;be very abundant, and the genus furnishes a very small element to thenbsp;flora.

Frond unknown; pinnules apparently subquadrilateral, narrowed gradually to the base and rapidly to the summit; midnerve in the lowernbsp;part of the pinnule strong, in the upper part dissolving into branches ;nbsp;lateral nerves going off very obliquely, branching near the midrib, turningnbsp;outward, and then by repeated branching and anastomosis forming long,nbsp;rather regular, elliptical to rhombic meshes, which fill the lamina.

Only two fragments of this plant were found. As, however, no detailed exhaustive search was made at this locality, and the amount ofnbsp;material was small, the rarity may be apparent rather than real. Thenbsp;shape of the pinnules is nearer that of S. rhoifoUa of the Rhetic than thatnbsp;of any other species of the genus known, but the anastomosis is morenbsp;copious than that of the Rhetic species. In copiousness of anastomosisnbsp;and in the shape of the meshes it is nearer S. ManteUi Schenk, of thenbsp;Wealden. It seems to lie between these two species. In the figure thenbsp;margin on the right-hand side appears to represent the original border ofnbsp;the leaf, but the other parts have been torn away.

Frond with five pinnules at the summit of a strong stipe, the right and left outermost pinnules smaller than the inner ones; pinnules narrowednbsp;gradually to a slender wedge-shaped base, and attached by a short petiole,nbsp;elongate-elliptical in outline and acute to acuminate at the tips, rarely subquadrate in outline; midnerve strong at base, dissolving towards thenbsp;summit into branches; lateral nerves leaving at an acute angle, curvingnbsp;out to meet the margin, repeatedly branching and anastomosing, so as tonbsp;form meshes, which are quite irregular in size and shape; meshes elongate-oblong or irregular subrhombic, some much larger than the others; betweennbsp;the nerves on the lower side of most of the pinnules numerous roundednbsp;or oblong minute elevations or dots occur, which can be seen distinctlynbsp;only with the help of a lens; these appear to be the fructification.

Localities: Road-side near Potomac Run; Kankey�s; Covington street, Baltimore.

At each of the two last-named localities a small fragment only was found. It is most abundant at the Potomac Run locality, from which all thenbsp;specimens figured come, but it is not very common even here. No specimen was found at the other or hill-side locality, only a few hundred feetnbsp;away. The dots look much like fructification, and I have no doubt thatnbsp;this is their character. This would place the plant in the Bictyopterisnbsp;group of Bolypodium. It would seem from tins that Sagenojjteris is a fernnbsp;and not a rhizocarp, as Schimper finally held it to be. Although thisnbsp;species has five pinnules at the summit of the stipe, it seems to be clearlynbsp;a Sagenopteris.

This plant, in the general shape of the pinnules and the character of the midnerve, reminds one strongly of the Neuropterids of the Coal Measures,nbsp;ddie shape of some of the pinnules, as in Pig. 16, is strikingly like thatnbsp;given by Brongniart in his Histoire for Glossopteris Pltillipsii (PI. LXI his,nbsp;Fig. .5), which he makes a Sagenopteris. The pinnules in some specimensnbsp;are much like those of Sagenopteris rhoifolia} The plant is decidedly

Jurassic in type. In Fig. 14, the lowest pinnule on the right-hand side belongs to the left hand, and forms the outermost one on that side. It has,nbsp;by displacement and pressure, been turned to one side and doubled backnbsp;under the summit of the stipe, so as to lie alongside of the outermost one ofnbsp;the right-hand side of that frond.

Frond unknown; shape of pinnules not seen, probably broadly elliptical or oval; stipe or petiole of pinnules apparently long; midnerve toward the base very strong, dissolving in branches towards the apex; areolationnbsp;very distinct, formed by lateral nerves which go off obliquely and curvenbsp;outwards to meet the margin, forking repeatedly, and anastomosing to formnbsp;meshes that are irregular in size and shape, being mostly elongate, oblong,nbsp;or subrhombic.

Plate CXXXVIII, Fig. 13, seems to represent the upper part of the specimen figured in PL CXXXIX, Fig. 1. The lamina of the leaf in thenbsp;lower part of this specimen has been torn away, leaving the midrib bare.nbsp;This appears to be a very large species of the genus.

Frond bipinnate or tripinnate, coriaceous; pinnse pinnately parted, pinnules or segments more or less constricted at base, decurrent on thenbsp;lower side, and forming a narrow wing to the rachis, entire, or incised andnbsp;lobed on the anterior margin ; nervation immersed, formed of a few nervesnbsp;branching flabellately from a common nerve at the base, diverging flabel-lately by repeated branching to fill the limb.

The above is very nearly Saporta�s diagnosis of the genus iSderopteris established by him. I modify the nervation only so as to include thenbsp;forms described in the next following pages, which clearly belong to thisnbsp;genus. As to the nervation, Saporta says, in Paleontologie Fran^aise,nbsp;Plantes Jurassiques, vol. 1, page 365, that the nerves come out obliquelynbsp;from the back side of the pinnules. This is not the case in all specimens.

even of those placed by him in the genus, as in PI. XLV, Fig. 2, given by him of Phillips�s Spliempteris lanceolata, which lie makes Scleropterisnbsp;riiillipsn. Saporta shows quite satisfactorily that Brongniart�s genusnbsp;Facliypteris, which has for its type P. ovata, was established under thenbsp;mistaken idea tliat the specimen furnishing the type had in the pinnulesnbsp;only a midnerve. It is identical with Phillips�s Neuropteris Icevigata. Thisnbsp;Saporta makes a Sderopteris with the name 8. Icsvigata.

Zigno, however, takes this plant as belonging to his genus DicJiopteris, because it appears to have the nerves, several in number and parallel, proceeding obliquely from the rachis. But an inspection of Zigno�s figurenbsp;shows that this idea of the nervation arises from the fact that he has notnbsp;drawn the true point of insertion of the lateral nerves, which is farthernbsp;within the apparent rachis, and at this point the nerves most probablynbsp;unite. Zigno has taken the margin of the wing for that of the rachis.nbsp;According to this, Pachypteris ought not to be considered as a genus.nbsp;Brongniart�s Pachypteris ovata would be Sderopteris Icevigata Sap., whilenbsp;Saporta makes Brongniart�s Pachypteris lanceolata, and Phillips�s Sphenopte-ris lanceolata, Sderopteris Phillipsii.

Frond bipinnate or tripinnate, arborescent; principal rachis stout and woody; ultimate rachises rather slender, straight, and winged; ultimatenbsp;pinnae alternate, linear, terminating abruptly in a pinnule like those lowernbsp;on the pinnae; pinnules or segments thick and leathery, narrowly elliptical,nbsp;acute, opposite, narrowed at base into a sort of petiole, decurrent to form anbsp;narrow wing; nerves immersed in the thick leaf-substance, inconspicuous,nbsp;diverging flabellately from a short common or mother nerve which doesnbsp;not extend beyond the base of the pinnules, branches once or twice foi�kednbsp;or simple.

Localities: Fredericksburg; lignite deposit near Potomac Run; fishing-hut above Dutch Gap Canal; Kankey�s; near Telegraph Station.

The plant is not very rare at Fredericksburg. The two fine specimens figured in PI. XXIX, Fig. 1, and PI. XXVIII, Fig. 0, come from that

locality. The leaf-substance of this plant is so thick and the epidermis so well preserved that on drying the leaves curl up and peel off from thenbsp;stone like paper, so that it is difficult to preserve the specimens. Thenbsp;nerves are seen with difficulty, but still they were clearly made out. Platenbsp;XXVIll, Fig. 6, gives a portion lower on the frond tlian the part figurednbsp;in PI. XXIX, Fig. 1. Plate XXVIII, Fig. 2, gives a small form fromnbsp;Fredericksburg with unusually remote pinnules.

All the features of this plant, except the nerves, agree exactly with those given by Brongniart for Pacliypteris lanceolata, and the resemblance tonbsp;Phillips�s Splienopteris lanceolata is striking.

This Potomac plant was evidently a large one. In this and the other species of the genus found in the Potomac beds there is no tendency tonbsp;the lobiiig of the pinnules given by Saporta as existing on the anteriornbsp;margin of some species.

Frond and pinnm not seen; pinnules linear-elliptical, alternate or opposite, oblong-subacute, gradually narrowed towards the base, verynbsp;long, decurrent, forming a narrow wing; leaf-substance leathery; nervesnbsp;comparatively fine, closely placed, forking from a common nerve at thenbsp;base, diverging slightly, branches deeply once or twice forked, with thenbsp;ultimate branches parallel.

This is probably only a variety of Scleropteris elliptica, but the differences are considerable. The figure gives�the summit of an ultimate pinna, which ends in a pinnule larger than those immediately below it on thenbsp;pinna. It is noteworthy that the pinnules diminish very rapidly in passingnbsp;towards the tip of the pinna.

Frond bipinnate or tripinnate; rachises comparatively stout; primary pinna; or those of the frond terminated by an ultimate pinnule like those

immeaiately below it on the principal rachis; ultimate pinnae opposite, terminated by a lobed tip, the pinnules of the lower portion having herenbsp;passed into more or less united lobes; pinnules small, opposite, thick, andnbsp;leathery, elongate-elliptical, acute, narrowed gradually to the base andnbsp;inserted by a sort of petiole, decurrent to form a narrow wing; nervesnbsp;inconspicuous from immersion, branching from a common point or a verynbsp;short nerve at the base of the petiole, diverging slightly, the secondarynbsp;branches forking once or twice.

This is a much smaller form than 8. elliptica, and more like 8. Pomeli Saporta, being, however, somewhat larger than that.

Frond bipinnate ? ; rachises slender, those of the ultimate pinnse winged; pinnules with leathery leaf-substance, oblong to elliptical, acute,nbsp;greatly narrowed at base, and decurrent to form a wing; lower pinnules cut very obliquely into ovate-acute lobes, which pass in the pinnules higher on the frond and towards the tips of the ultimate pinnae intonbsp;triangular and shallow acute teeth; the ultimate pinnm (Fig. 3) terminatenbsp;with an oblong pinnule, which has at its summit three teeth; nerves ofnbsp;the pinnules composed of a slender midnerve, which sends off alternatelynbsp;into each lobe or tooth a deeply forked lateral nerve, sometimes havingnbsp;one of the branches forking again.

This fern shows a curious blending of the features of 8cleropteris and Cienopgt;teris, standing midway between them.. Perhaps it would be betternbsp;to make it a new genus.

Frond bipinnate or tripinnate; pinnm broadly linear-lanceolate, pinnate, and pinnatifid; pinnules attached by the entire base, sliglitly decurrent, lower ones separate, upper ones slightly united at base, slightly curved

forward; leaf-substance thick, mai-gins entire or with spinous teeth; nerves several, arising from the rachis either separately, or from a common point,nbsp;or from a short parent nerve, branching one or more times, branches turnednbsp;slightly outward, or with a central nerve that sends off on each sidenbsp;branches that diverge flabellately.

The forms from the Potomac flora that I have placed in the genus Ctenopteris, with the amended description given above, differ somewhat fromnbsp;tlae typical form on which Brongniart founded the genus, viz, Ctenopterisnbsp;cycadea Brong., and the species of Saporta, C. grandis, but stand verynbsp;near to the latter.

These Potomac species apparently are composite in type and unite some of the features proper to several genera of ferns. They have, however, so many of the characters of Ctenopteris that it seems proper to placenbsp;them in that genus.

Perhaps the differences shown when they are compared with the typical ctenopterids are due to modifications produced in the genus as timenbsp;passed, for we must remember that Ctenopteris cycadea and C. grandis arenbsp;Liassic fossils, while the Potomac forms are much younger. The divergences are of such a nature as to suggest this relationship, for the chiefnbsp;ones consist of a greater complexity produced by the differentiation of thenbsp;nerves, which tends to produce a midnerve, and by the development ofnbsp;teeth on the margins of the pinnules or segments

Although from the general character of these plants I I'egard them as ferns, still, so long as they show no fructification, it is quite possible thatnbsp;they may be cycads. Schimper^ well says that the tripinnate character ofnbsp;the leaf of the genus does not necessarily exclude it from the cycads, fornbsp;the cycad genus Bowenia has bipinnate leaves. Bowenia resembles thenbsp;Potomac plants more strongly than the forms on which Brongniart foundednbsp;the genus, for this cycad has leaflets cut away obliquely in front andnbsp;nerves which diverge from a common point at the base of the pinnules,nbsp;features found in the Potomac plants; and, what is more significant, somenbsp;of the pinnules of Bowenia have at least one spinous tooth, much likenbsp;those of the Potomac plants.

Saporta calls attention to the resemblance of the Jurassic ctenopterids to the odontopterids of the Carboniferous, and says that there is muchnbsp;difficulty in giving any good distinction between Ctenopteris and Zigno�snbsp;genus Dichopteris from the Oolite. He thinks it possible that Dichopterisnbsp;may represent Ctenopteris in the Oolite, the main difference being thatnbsp;Dichopteris has its pinnules narrowed at base. Saporta also remarks thatnbsp;Scleropteris is near to Ctenopteris. The Potomac plants bring these generanbsp;still nearer, supplying connecting links, for we find some with the characters of each of these genera predominating, and they graduate into onenbsp;another. They show that the features relied upon to distinguish Scleropteris, Ctenopteris, and Dichopteris have in the main but little value.nbsp;Scleropteris may remain a distinct genus, but, as has been suggested, therenbsp;seems to be no good reason why Dichopteris should not be united tonbsp;Ctenopteris; for, as Saporta says, the bifurcation of the frond of the formernbsp;may have been accidental. If we omit the slight union of the pinnulesnbsp;at base and the absence of teeth, the resemblance between the nervationnbsp;of Dichoj)teris Visianica,^ its shape, and the attachment of the pinnules, andnbsp;these features in some of the Potomac ctenopterids is most striking. Wenbsp;have the same slight forward curvature of the pinnules, the oblique cuttingnbsp;away in front, the slight decurrence below, and the same mode of insertionnbsp;of the nerves. Tlie nerves differ only in the more copious branching ofnbsp;the centi�al ones of the Potomac plants.

Heer^ gives figures of plants which he places in his cycadean genus Cienidium. These, and more especially the species C. dentatum, resemblenbsp;in some points the Potomac plants; bnt in Heer�s plants the cycadean features predominate, and they certainly belong to a genus distinct from thatnbsp;of the Potomac fossils. Phillips�s Odontopteris Leckenhji Zigno (Geol. ofnbsp;Yorkshire, p. 218) may also be compared with these plants. The speciesnbsp;Ctenopteris ItierP Sap. seems to belong to a type quite different from C.nbsp;grandis and C. cycadea, Iiaving the nervation only in common. C. Dierinbsp;is much more fern-like than the two latter.

The Potomac fossils give more of the frond than the species hitherto known, and thus add a good deal to our knowledge of this curious genus.nbsp;Unfortunately no trace of fructification was seen.

Frond large, arborescent, bipinnate or tripinnate; principal rachis very strong, striate; ultimate pinnte with strong rigid rachises, alternate,nbsp;terminating in a lobed segment, the pinnules passing into lobes more ornbsp;less united towards the ends of the ultimate pinnge; pinnules thick andnbsp;leathery, those of the lower and middle portions of the pinnge attached bynbsp;the entire base, slightly decurrent, separate, cut away obliquely above,nbsp;alternate to subopposite, gradually diminishing towards the summit of thenbsp;pinnge in size and depth of toothing, not sensibly narrowed at base, oblong-acute, curved slightly forward, terminating in a large ovate to subtriangu-lar acute tooth. The pinnules usually show two acute or spinous teeth onnbsp;each side, a couple near the base, and a second couple near or at the summit of the pinnule, the associated members of the couples being oppositenbsp;or subopposite. Sometimes there is an additional tooth on the posteriornbsp;margin below the upper one, and sometimes the terminal tooth is enlargednbsp;to an oblong lobe (see PI. LXI, Fig. 4), which is slightly notched; nervesnbsp;several, departing separately from the principal rachis along the entirenbsp;width of the base of the pinnule, the outermost ones once forking andnbsp;curving outwards, the inner ones forking deeply several times and slightlynbsp;diverging flabellately, the ultimate branches nearly or quite parallel, long,nbsp;and slender.

This splendid plant is not uncommon at the first-named locality, and is found in small bits only at Potomac Run. All the specimens figurednbsp;come from Fi'edericksburg. The specimens show a black, glossy plant-matter, which peels off like paper from the stone, and indicates that the epidermis was dense and durable. A thick coriaceous epidermis covered thenbsp;main rachis and all pai�ts of the plant. The nerves are not usually distinctly seen, being obscured by the thick epidermis. The form given in

PI. LXI, Fig. 4, differs from the typical forms in having the termination of the pinnules an oblong lobe, which is slightly notched or toothed. Figurenbsp;5 of the same plate appears to be the summit of an ultimate pinna, differingnbsp;in the ti'ilobate terminal pinnule from tlie normal termination, as shown innbsp;PI. LXIIl, Fig. 1, where the lobes gradually diminish in size towards thenbsp;summit.

Fi�ond bipinnate or tripinnate, probably arborescent; rachises stout, strongly ridged or keeled; ultimate pinnae subopposite; leaf-substancenbsp;thick; pinnules comparatively short and broad in proportion to theirnbsp;length, opposite or alternate, slightly decurrent, distinct to the base ornbsp;slightly united, attached by the entire base, rounded obliquely on thenbsp;upper side at base, slightly curved forwards, posterior margin nearlynbsp;always free from teeth, terminating in a triangular tooth, with an acutenbsp;tooth on each side of this at the summit of the pinnule, and with an acutenbsp;or spinous tooth about midway on the anterior margin; nerves proceedingnbsp;from a common point on the rachis of the ultimate pinme, branching several times and diverging slightly, the ultimate branches long and nearlynbsp;parallel.

This plant has a very stout principal rachis, but the species is decidedly smaller than C. insignis, and shows some important points of difference from it. On nearly all the pinnules there are no teeth on the posterior margin of the pinnules, and only one on the anterior margin. The most important difference is in the nerves. They form two principalnbsp;nerve-bundles, which depart from a common point and not from the entirenbsp;base of the pinnule. Thus they show a tendency to form a midnerve without actually developing one. In this feature there is an approach to thenbsp;Scleropteris type.

Fronds small, arborescent, bipinnate or tripinnate; principal rachis strong, rigid; ultimate pinnae with rachises strong towards the base and

much attenuated towards the summit, alternate to subopposite, and terminating in a slender toothed or lobed segment; pinnules small, separate in the lower part of the ultimate pinnae, but united at base in the upper partnbsp;of the same, attached by a base slightly narrowed and decurrent, cut awaynbsp;obliquely on the upper side of the base, inclined forwards, alternate tonbsp;opposite, Towards the summit of the ultimate pinnae the pinnules diminishnbsp;in size and in the number and depth of the teeth, the uppermost onesnbsp;being entire and elongate-oblong in shape. The lower and middle pinnulesnbsp;of the ultimate pinnae are generally subrhombic in form and vary somewhatnbsp;in the number and form of the teeth; they terminate in a comparatively largenbsp;triangular or ovate tooth or lobe, which is generally entire and rarelynbsp;slightly dentate, and generally show two more or less acute teeth on eachnbsp;side and in pairs, a pair near the base and one near the summit, the members of the pairs being opposite or subopposite. Sometimes additional teethnbsp;appear, generally on the posterior margin of the pinnules; principal nervesnbsp;several, departing separately from the rachis of the ultimate pinnae so as tonbsp;fill the central portion of the base of the pinnules. The outermost ones forknbsp;once and curve outwards, the inner ones fork several times and divergenbsp;slightly in a flabellate manner; the ultimate branches are short and divergenbsp;strongly ; all the nerves strong.

This plant is in many features like Ctempteris insignis. It differs from this mainly in the small size of the pinnules, the greater variability of thenbsp;teeth, and in the character of the ultimate forking of the nerves. In C.nbsp;insignis the ultimate branches of the nerves are long, slender, and nearlynbsp;parallel. Perhaps this is merely a small variety of that plant.

Frond unknown; pinnules oblong to subelliptical, slightly curved forwards, subacute, obliquely cut away on the anterior margin at base, decurrent on the lower side, separate to the base in the lower portions ofnbsp;the ultimate pinnse, united slightly in the upper ones, which are muchnbsp;diminished in size ; nerves several and distinct, departing from the rachis

at several points, the outer ones once or twice forking and turned outwards, the central nerve branching several times, branches flabellately diverging; all tlie ultimate branches from deep forking are long.

This plant makes a close approach to Zigno�s I)iclio])teris Visianica, the main difference being the more copious branching of the central nerve, asnbsp;shown in the pinnules of PI. LXV, Fig. 3, magnified in Fig. 3^ In thatnbsp;shown in PI. LXII, Fig. 2, from Fredericksburg, the pinnules are somewhat falcate, and are united at base. It is apparently a fragment of thenbsp;terminal portion of a pinna..

Frond unknown; ultimate pinnge long, with rather stout rachises, pinnules linear or narrowly oblong, in proportion to width quite long, slightly curved forwards, separate to the base, or united to form a wing on thenbsp;rachis of the pinnae, cut away obliquely on the upper side at base, andnbsp;slightly decurrent on the lower side, attached by the entire base, terminated by from one to three acute or spinous teeth, and having a varyingnbsp;number of the same placed irregularly on both margins. The nervesnbsp;proceed from the rachis at different points along the entire base of the pinnules; the outer ones simple or forking once, the central ones forking several times, the ultimate branches being long, slender, and slightly diverging.

There is some difference in the two specimens figured, which, however, may be due to different positions on the frond.

Frond unknown; rachis of the ultimate piniuc very broad but not apparentl}^ very woody; pinnules placed very remotely, opposite, goingnbsp;off obliquely, very long, linear, narrowed gradually and slightly towardsnbsp;the base and slightly decurrent, tips not seen; nerves not well made out,nbsp;but apparently as shown in Fig. 5�; that is, several, departing independ-

ently from the racliis and forking near the base; the branches, so far as seen, simple, and nearly parallel.

This is another of those curio us forms which, as they stand nearest to Ctenojpteris, are placed provisionally in this genus. The obscurity aboutnbsp;the nerves is Avholly confined to their character at the attachment of thenbsp;pinnules. They were not distinctly seen at this point, and may be notnbsp;forking there but separate. The plant is very much like the genusnbsp;Enceplialartos, and especially resembles E. tridentatus Lehm. It may reallynbsp;belong to this genus.

ZAMIOPSIS, gen. nov.

Fronds large, bipinnate to tripinnatifid; leaf-substance leathery and thick, covered with a dense durable epidermis; rachises strong, rigid, andnbsp;keeled on the lower surface, often with ridged or raised mai�gins on thenbsp;upper surface; penultimate pinnae very long, ultimate pinnae or pinnulesnbsp;usually closely placed, narrowed to the base, mostly linear-lanceolate ornbsp;oblong-lanceolate, the lower ones generally cut obliquely into pinnulesnbsp;which are denticulate, but pass above into denticulate or spinous teeth andnbsp;terminate in two or more spinous teeth; nerves of the pinnules and lobesnbsp;mostly composed of a midnerve which goes off very obliquely and curvesnbsp;strongly outAvards, sending off obliquely and alternately lateral branches,nbsp;Avhich are forked or simple and curve upwards towards the summit of thenbsp;segment; in the lobes and teeth the lateral nerves go off very obliquelynbsp;and fork once or twice, having very long ultimate branches; nerves,nbsp;although fine, very distinct.

This curious type of ferns, if ferns they are, reminds one of the cycadean genus Stangeria in some respects, but in the nature of the lobesnbsp;and teeth they differ from Stangeria. In most species the nerves towardsnbsp;the upper portion of the ultimate pinnm or pinnules are very oblique andnbsp;have long slender branches, Avhile in the lower or basal portions they formnbsp;nerve-bundles that curve more or less strongly outwards to meet the margin of the pinnule or reduced pinna. The plants shoAV a curious blendingnbsp;of the features of cycads and ferns, with a predominance of the latter.

In tlie branching of the rachis we have the fern rather than cycadean character, although Bowenia shows that this is not necessarily solely anbsp;fern feature. AVe can hardly assuiue that Boivenia is the only bi'anchingnbsp;cycad that ever existed. It is more natural to suppose that it is a survivornbsp;of a group of branching cycads that once possessed nuriierous forms.nbsp;The nervation of the lower portions of the pinnules is rather that of fernsnbsp;than of cycads, bnt Stangeria shows that similar nerves may exist innbsp;cycads. The very long, slender, deeply forking nerves in the summits ofnbsp;the pinnules are similar to those of cycads. The peculiar spiny teeth arenbsp;decidedly like those of cycads, but the teeth pass below on the frond intonbsp;lobes, and these lower down graduate into segments that we may callnbsp;pinnules, and this feature is clearly fern-like. The nerves are immersednbsp;in the dense leaf-substance, so that they are often obscured.

The singular plant Zamiopsis laciniata, given on PI. LXVI, has so many features that cause it to differ from the typical forms of Zamiopsis,nbsp;that it may well be questioned whether or not it should be made a newnbsp;genus; but as it has some features allying it to the typical Zamiopsis, Inbsp;place it with a good deal of hesitation in that genus. So long as nonbsp;fructification is found with these plants their true position can not benbsp;positively determined; meantime they may be placed provisionally amongnbsp;the ferns. This type forms quite an important element in the Potomacnbsp;flora.

Plate LXI, Fig. 7 ; Plate LXII, Pig. 5; Plate LXIV, Fig. 2; Plate LXVII, Fig. S.

Frond large, arborescent 1 ; principal rachis keeled on the under side, strongly ridged on the upper margins, probably tripinnate; pinnules ornbsp;reduced pinnaj alternate, attached by the middle of the narrowed base,nbsp;oblong, terminated by usually two acute shallow teeth in the basal portions, cut down nearly to the midrib into ovate denticulate lobes or pinnules; up higher on the pinnules or reduced pinnae these pass into ovatenbsp;teeth, which become more and more shallow. On the basal lobes ornbsp;pinnules there are on each margin two or three shallow spinous teeth;nbsp;midnerve of the ultimate pinnae or pinnules strong at base, rapidly atten-

uated towards the summit, and dissolving into branches near the tips; lateral nerves of the basal toothed pinnules or lobes composed of a nerve-bundle which goes off very obliquely from the lower portion of the lobenbsp;or below it, branching several times, curving strongly away from thenbsp;midnerve of the pinnule or reduced pinna, slightly diverging, the ultimatenbsp;branches going into the teeth, and mostly simple. In the lobes towards thenbsp;upper end of the pinnules the nerves become less and less copiouslynbsp;branched, being finally reduced to nerves forking only once or twice.

This plant must have been a very large one. Plate LXI, Fig. 7, and PI. LXIV, Fig. 2, give probably fragments of compound pinnae. Thenbsp;pinnules cut into lobes are most probably reduced ultimate pinnae, thenbsp;lobes representing what are, in portions lower down, pinnules separate tonbsp;the base; possibly these fossils may be a variety of the next following,nbsp;Zamiopsis insignis, but there seem to be no forms establishing a jmssagenbsp;into that species.

Plate LXII, Fig. 3; Plate LXIV, Figs. 1, 3; Plate LXV, Figs. 4-6; Plate LXVI, Fig. 2; Plate

Frond very large and spreading, probably tripinnate; leaf-substance of the pinnules thick and leathery; epidermis, covering the principal rachis,nbsp;as well as the other portions of the plant, thick and durable; principalnbsp;pinnae going off at very nearly a right angle, very long, with a very stout,nbsp;rigid rachis, keeled on the lower side, with marginal ridges on the uppernbsp;side. The ultimate reduced pinnae or pinnules pass towards the summit ofnbsp;the penultimate pinnae into much reduced toothed pinnules, united at basenbsp;and decurrent; ultimate pinnae or pinnules oblong, much narrowed at basenbsp;in the lower ones, and attached by the middle of the base, alternate, varying in size, extent of toothing, and remoteness with their position on thenbsp;frond, lower ones cut deeply and obliquely into oblong or subquadrangu-lar lobes or pinnules, which usually have near the tips on each side shallow spinous teeth, and end in a comparatively large ovate-acute tooth.nbsp;Sometimes only one tooth is found on the lobes, and that occurs on the

upper margin; this varies with the position of the lobes on the pinnae and the frond; on the lower lobes and pinnae it is broadly triangular, rathernbsp;deeply cut, and directed outwards; in the upper pinnae and lobes it isnbsp;minute, shallow, and spinous; in the upper portions of the frond the lobesnbsp;end in or graduate into spine-like teeth, which are sometimes much prolongednbsp;and quite slender, these teeth directed forwards or outwards are single ornbsp;double. The reduced ultimate pinnae or pinnules end variously, either innbsp;two or more acute teeth or in an ovate-denticulate lobe; midnerve of thenbsp;ultimate pinnae or pinnules strong towards the base, rapidly much attenuated higher, and at the summit dissolving into branches; nerves of eachnbsp;lobe or pinnule of the basal portions of the lower pinnae or pinnulesnbsp;composed of a nerve-bundle which goes off very obliquely from thenbsp;rachis below the base of the lobe or pinnule, curving strongly outwards,nbsp;forking near the base, with each branch forking deeply once or twice again.nbsp;Towards the summit of the ultimate pinnae the lateral nerves become verynbsp;oblique, do not curve so suddenly and strongly outwards, but continue fornbsp;a long distance, more or less in the direction of the axis of the pinna, arenbsp;forked several times with long branches, foi�ming indeed the branches intonbsp;which the midnerve splits up. In the upper toothed pinnae the midnervenbsp;(see PI. LXIV, Figs. 1�, l�^) continues only a little more than one-third ofnbsp;the length of the pinna. It is split up into very obliquely placed, slightlynbsp;diverging, and very deeply forking branches, which fork once or twice, andnbsp;have very long, slender, ultimate branches. The lateral nerves from thenbsp;lower portions of these pinnae, go off very obliquely, fork once or twice,nbsp;and have very long, slender, ultimate branches.

The specimens obtained of this plant show that it must have attained a very large size. The fragment figured in PI. LXIV, Fig. 1, is probablynbsp;a portion of a compound pinna of large dimensions. The specimen givennbsp;in PI. LXV, Fig. 4, which is a portion of probably a penultimate pinna,nbsp;shows that these must have been in some cases very long. The epidermisnbsp;over the pinnules and rachises of PI. LXIV, Fig. 1, was so thick and durable, that it could be peeled ofiquot; like paper. Plate LXIV, Fig. 3, seems tonbsp;show a fragment of a penultimate pinna, forming the lower portion of one

corresponding to that depicted in PI LXV, Fig. 4. Plate LXIV, Fig. 3, shows some irregularity in the spacing of the penultimate pinnae or pinnules, the central ones on the left-hand side showing an abnormal crowding. Plate LXVII, Fig. 7, appears to be an ultimate pinna or pinnulenbsp;from still lower on the frond than any of the others, and the lobing isnbsp;irregular, two of the lobes from the middle of the specimen on the right-hand side being cut deeply into falcate, narrowly oblong, or ovate lobes.nbsp;While the general plan of the lobes and teeth is the same throughout, somenbsp;variation is shown in the number, arrangement, and shape of the teeth.nbsp;Thus we have in PI LXV, Fig. 5, the lobes or incipient pinnules sub-quadrangular, curved forward, with a terminal ovate tip, and on the exterior margin near the tip a broadly triangular tooth directed outwards.

Frond unknown; ultimate pinnse or pinnules very long, ensiform, slightly falcate, actiminate ; margins of the pinnules cut into shallow, narrowly ovate single or double teeth, midnerve stvong towards the base andnbsp;vanishing towards the ends of the pinnules, splitting up into branches, innbsp;the upper portion not placed centrally in the pinnules ; lateral nerves distinct, going off very obliquely, curving outwards and forked once or twice,nbsp;with the ultimate branches long and slender.

This may possibly be the summit of a pinnule of Zamiopsis insignis, but it has features not seen in that species, and the pinnule was evidentlynbsp;much longer than any seen on it. The eccentric position of the midnervenbsp;and the convex expansion of the lower mai-gin near the summit of the pinnules are peculiar features.

Frond very large and wide-spreading, probably arborescent; ultimate pinnm alternate, the lower ones very long, rapidly diminishing in length

and size ii ascending towards the summit of the principal pinnse, having a distinctly winged rachis, and terminating in a variously shaped segmentnbsp;formed of united pinnules or lobes, usually three in number; pinnules verynbsp;variable in size and shape, mostly long, ribbon-shaped, sliglitly narrowed tonbsp;the base and attached by the entire base, decurrent, and united to form anbsp;wing, cut very obliquely into a few lobes of varying depth, which arenbsp;elongate-oblong or narrowly ovate in shape, and nearly always placed onnbsp;the posterior margin of the pinnule. The lobes toward the summit of thenbsp;pinnules pass sometimes into acute triangular teeth, which are turned outwards. The pinnules at the summit of the ultimate pinnae pass into more ornbsp;less united lobes, which vary a good deal in shape, being sometimes muchnbsp;naiTowed and even wedge-shaped at base, and incised into a varying number of irregularly shaped teeth ; nerves of the pinnules departing from anbsp;short mother nerve at the base of the pinnules, forming three branches,nbsp;these diverging slightly in a flabellate manner; branches very long, slender,nbsp;but distinct, outer branches simple or once or twice forked, the inner onenbsp;forking several times and approaching the character of a midnerve ; leaf-substance thick and leathery.

This splendid but very peculiar fossil unites some of the features of Zamiopsis with some of those of Ctenopteris. It really stands intermediatenbsp;to typical forms of these two genera. It, also shows some of the featuresnbsp;of Scleropteris, and it hence belongs to quite a comprehensive type of plants.nbsp;As the nervation is not essentially different from that of Zamiopsis, it seemsnbsp;best to place it provisionally in that genus.

The plant is a remarkable one. In its pinnules and longer lobes, so far as the shape goes, it reminds one of Saporta�s Stenopteris desmomera, butnbsp;the nervation is very different. Some of the pinnules towards the tips ofnbsp;the lower ultimate pinnae are narrowly strap-shaped, and show a very considerable length without any lobing or toothing. But as the tips of thesenbsp;are wanting, it is possible that they may possess teeth up higher. Figurenbsp;6, the upper portion of an ultimate pinna, and also Figs. 5, 7, show hownbsp;irregular the toothing and shape of the pinnules, here reduced to lobes,nbsp;become in the terminal portions of the ultimate pinnae.

Frond bipiniiate or tripirmate; principal rachis with a strong wing; primary pinna terminating abruptly in a large incised pinnule similar to thosenbsp;lower down; pinnules petiolate, attached by the midnerve, prolonged intonbsp;a stout petiole, alternate, cut obliquely into oblong or subelliptical obtusenbsp;pinnules, in the lower part of the ultimate pinnae turned outwards. Thesenbsp;graduate in the upper parts of the same into lobes and teeth of the samenbsp;general character. The summit of the ultimate pinna is a broad oblongnbsp;segment ending in several shallow subacute teeth formed by the union ofnbsp;the lobes at the summit; the ultimate pinnae in passing towards the summit of the penultimate ones diminisli much in size, the pinnules and lobesnbsp;passing finally into teeth; lateral nerves in each pinnule and lobe consisting of a nerve-bundle which goes off very obliquely from a point near thenbsp;lower end of the pinnule or lobe, branching near the insertion, and curving out to enter the pinnule or lobe, the branches forking again once ornbsp;twice, with the ultimate nerves very long and slender, owing to their deepnbsp;forking.

This is another of the peculiar cycad-like ferns which form such a striking feature in the Potomac flora. Possibly it is a new genus, and Inbsp;place it with doubt provisionally in the genus Zamiopsis. The principalnbsp;rachis has on each side a strong succulent wing or mai�gin (see Fig. S'*).nbsp;The nerves agree fully with those of Zamiopsis.

PHANEROGAMS.

The cycads of the Potomac flora, although presenting a considerable number of species, by no means equal the Goniferoi in that respect, but itnbsp;is especially in the number of individuals that this group contrasts withnbsp;the Coniferce. With the exception of Dioonites the species, when found,nbsp;are among the great rarities at the different localities. As the specimens

are generally very fragmentary and apparently injured by transport, it is quite possible that the comparative rarity of cycads is apparent rathernbsp;than real, being due to the accidents of preservation, which were notnbsp;favorable to these plants. Although not equaling the ferns and conifers,nbsp;the cycads are present with a development sufficient to form an importantnbsp;element in the flora and to add greatly to the Mesozoic aspect of thenbsp;vegetation.

ANOMOZAMITES Schimper.

Leaves comparatively small, linear or ribbon shaped, sometimes (the younger?) entire, mostly cut into irregular segments; lamina of the leafnbsp;attached laterally, sometimes undivided or only partially divided, butnbsp;most often divided into rectangular lobes unequal in size, which, especiallynbsp;in the lower ones, are rounded; nerves going off at i-ight angles, simple,nbsp;and parallel. The segments have sometimes a corded border.

This description, which is very nearly that given by Schimper^ for Anomozamites proper, typified in Anomozamites inconstans Gl�ppert, fitsnbsp;exactly a few of the smaller Tseniopteris-like cycads of the Potomac flora.nbsp;The forms thus limited range, according to Schimper, from the Rhsetic tonbsp;the Wealden. From the genus pi�oper, having the above description,nbsp;certain large leaves are excluded by Schimper in the work above quoted,nbsp;and placed in a subgenus, Platypterigium. These will be noticed furthernbsp;on. In the genus proper of Anomozamites there are two species in thenbsp;Potomac flora.

Leaves comparatively narrow, 4�quot;* wide, I�ibbon-shaped at the tip, narrowed rapidly; � leaf-substance thin, lower portions of leaf not seen;nbsp;midnerve moderately sti'ong; lateral nerves going off nearly at right angles,nbsp;simple, parallel, arched slightly forward, towards the tip of the leaflet goingnbsp;off more obliquely and arched forward more strongly, slender, but distinct.

The small fragment (Fig. 2) occurs in the plants collected by Meek at Baltimore, probably at Federal Hill. It is the smallest of the Potomacnbsp;Anomommites and may be a young form of some of those found in thenbsp;Platypterigiimi subgenus, for it shows no tendency to subdivision of thenbsp;lamina.

Leaves pi�oportionally very long, of medium width, 37�� wide, no segmentation visible; the nerves are simple and go off nearly at rightnbsp;angles, and near the margin curve slightly forward, thin, but distinct; leaf-substance thin; midnerve strong.

The leaves of this plant are considerably larger than those of A. an-gustifolius. No tendency to segmentation is shown, and it may be a young form of one of the large Platypterigia.

Leaves large, up to two feet and more in length, and half a foot wide; lamina of the leaf thin, divided into segments of unequal size, that arenbsp;rounded or obtusely rhombic in shape; nerves parallel, simple, andnbsp;forked; forms are Pteropliyllum Braunsii Schenk., P. princeps Oldham andnbsp;Morris, etc.nbsp;nbsp;nbsp;nbsp;,

This description of Schimper for the subgenus agrees well with certain large leaves that are rather common at Fredericksburg. Schimper says that these leaves may be compared with the split leaves of Macrotai-niopteris, and such I for�some time took them to be, but was finally compelled to think that the segmentation was not the result of accidentalnbsp;fissuring. The individuals of the species of this genus are very muchnbsp;more akundant than those of the species of Anomozaniites proper. It isnbsp;peculiar that I could find no specimen showing the ends of the leaves, andnbsp;the base of the leaf also was never found. Parts of the middle portions ofnbsp;the leaves were by far the most common. The plants collected by Professor Uhler at Fredericksburg, and which were lost in transmittal to Newnbsp;Orleans, contained a fine tip of one of these leaves.

These Platypterigia must have attained a great size, rivaling that of Macrotceniopteris magnifolia of the Virginia Rhmtic. For some time, whennbsp;only very imperfect specimens had been found, I tiiought that these werenbsp;fissured leaves of that or a nearly allied plant.

My recollection of the lost tip of the leaf in Professor Uhler�s collection is not definite enough to enable me to describe it accurately, for I examined it only casually, expecting to be able later to critically study it.nbsp;The leaf tapered gradually to a subacute point, much as do some of thosenbsp;of M. magnifolia.

The larger specimens of this subgenus probably formed portions of leaves that must have been over two feet long (60��) and a half foot widenbsp;(lb��). The rachis is very stout and wide, with a ridge or cord running innbsp;the middle on the lov/er side. The upper side is smooth, or with a marginalnbsp;ridge on each side. Fragments of leaves 25�quot;' long, and without sensiblenbsp;diminution in their width, have been obtained, and some specimens 14�'quot;nbsp;wide were seen. Midribs with a width of Oquot;quot;quot; have been found, and a portion of a petiole showed the width of 13��'�. The nerves towards the base,nbsp;as shown in PI. XXXI, Fig. 2, are more oblique in their course than in tlienbsp;middle of the leaf. The ridge in the center of the midnerve on the undernbsp;side seems to be due to the woody bundle of the true midnerve, showingnbsp;by pressure tlmough the thick epidermis. This epidermis on the midnervenbsp;is striated parallel with the length of the leaf. None of the lateral nervesnbsp;are furcate even at base.

Plato XXX, Fig. 8; Plate XXXI, Figs. 1,4; Plate XXXII, Figs. 1, 2; Plate XXXIII, Fig, 1; Plate

Leaves very large, probably 60�'quot; and more in length, and as much as 20�'quot; in width; leaf-substance very thick and membranaceous ; midnervenbsp;moderately strong, covered with a thick, dense epidermis, which is striatednbsp;parallel with the length of the leaf, an d which makes the midnerve appearnbsp;wider than it really is, on the lower surface sometimes appearing ridgednbsp;in the middle, on the upper side smooth or corded on each margin at thenbsp;attachment of the lamina of the leaf; laminae entire, or more commonly cut

into segments of varying width, that ai'e rectangular, irregularly quadrilateral, or subrhomhic in shape, and have often the posterior or outer margins obliquely rounded off; nerves very fine and placed very closely together, so that two or three occur in the space of 1��, going off nearly atnbsp;right angles, curving very slightly forward, parallel.

This splendid plant has yielded a number of specimens, but all of them, no doubt owing to the great size and to the fragility of the leaf,nbsp;show only small portions of the plant. The base and tip of the leaf werenbsp;in no case found, although carefully sought for. The specimen mentioned as 25quot;� long, with no sensible diminution in width, belonged to thisnbsp;plant. One specimen showing only half the lamina of the leaf was 9��nbsp;wide (see PI. XXXV, Fig. 2). This indicates a leaf 20�� wide. The tipnbsp;seen in Professor tJhlei-�s collection seems to have belonged to this species.nbsp;This plant has the same kind of vaguely defined midnerve that wasnbsp;described in Contributions to the Knowledge of the Older Mesozoic Flora ofnbsp;Virginia, Mon. U. S. Gleol. Survey, vol. 6, as belonging to Macrotceniopterisnbsp;magnifolia Rogers, of the Older Mesozoic or Rhsetic flora of Virginia. Itnbsp;is due to the dense epidermis and leaf-substance at the junction of the lamina of the leaf and the midnerve, which hides the insertion of the nervesnbsp;and v.ddens the apparent midnerve.

The nerves, although exceedingly slender and closely placed, are sharply defined and have only one woody bundle, differing in this pointnbsp;from those of the Rhmtic fern. They are usually one-half millimeternbsp;apart, although sometimes only one-third of this. Fragments of the petiolenbsp;were very rarely seen.

This plant may be compared with Nilssonia Johnstrupi, Heer^ It is very much like Pterophyllum p?-inceps Oldham and Morris,^ and alsonbsp;strongly resembles Pterop)hjllum Braunsii Schenk. Both of these arenbsp;Rlisetic plants, and both are placed by Schimper in his subgenus Flatyp-terigium. Nilssonia Johnstrupi seems to be a Platypterigium surviving intonbsp;the Middle Cretaceous.

Leaf large, rivaling the dimensions of P. clensimrve; leaf-substance thicker and more coriaceous than that of P. densinefve. It is comparativelynbsp;strong and coriaceous; midrib well defined, rounded, and prominent,nbsp;rigid, and without apparent dense epidermis; nerves comparatively strong,nbsp;towards the base of the leaf going off more obliquely, higher and towardsnbsp;the middle of the leaf going off at a right angle, simple, straight, and parallel, more remote than those of P. densinerve, being apart.

This fine plant is much rarer than P. densinerve. It is a more robust species than the latter. It is not so prone to segmentation as that species,nbsp;possibly from its denser and stronger leaf-substance. One specimen was seennbsp;11�� wide, and in a length of 12¹�quot; showed no division into segments. Inbsp;have named the plant in honor of Prof William B. Eogers, who first studiednbsp;the geology of the Potomac formation and called attention to its plants.

Leaves small or of medium size, in growing old becoming detached ; leaflets attached to the upper side of the rachis by a callosity, somewhatnbsp;contracted or rounded at base, almost cordate there, linear or ovate-lanceolate, acute or obtuse, margins entire, of firm consistency.; nervesnbsp;simple or forked, the middle ones parallel, diverging only towards tlienbsp;summit, the lateral ones ending in the margin.

This description, which is essentially that given by Schimper,^ applies to some detached leaflets found in the Potomac flora. They are alwaysnbsp;among the rarest of fossils in this flora, appearing only in sparingly dispersed fragments. They form a very inconsiderable element in the Potomac flora, being found mostly at Fredericksburg.

Plate LXVII, Fig. 1; Plate LXIX, Fig. 2; Plate LXX, Fig. 1; Plato LXXV, Pig. 3; Plate LXXVI, Fig. 7; Plate LXXVIII, Fig. 6; Plate LXXXIV, Fig. 7.

Leaflets very long, attaining the length of 20.5'^� and a width of 24��, at base abruptly subcordate, in shape ensiform, sometimes curved,

acute; nerves very numerous and closely placed, fine but distinct, forked at base or simple, occasionally forked a little higher, parallel after forking.

Localities: Fredericksburg; Kankey�s; banks of Dutch Gap Canal; fishing-hut above the ctinal; near Telegraph Station.

This fine plant is the most common cycad at Fredericksburg, where it is not very rare. PI. LXX, Fig. 1, is the most complete specimen seen,nbsp;but in this the nerves unfortunately were obscure. It is almost alwaysnbsp;found in the form of detached fragments of the basal portions of leaves,nbsp;showing that they were very deciduous and disarticulated, so as to leavenbsp;the detached base more or less heart-shaped. They were apparentlynbsp;attached by a callosity. In PI. LXXVI, Fig. 7, a small bit of the rachisnbsp;may still be seen attached to the base of the leaf When the leaves havenbsp;been detached from the callosity by which they were attached, tlieir basesnbsp;have a cordate sinus. The plant does not seem to be nearly allied to anynbsp;described fossil.

Leaves broadly elliptical, short, acute, abruptly narrowed at base and attached by a callosity; nerves simple or forking at the very base, verynbsp;strong, distant, parallel to near the apex, where they are more crowded.

This is a well-marked form of a type a good deal like some of the species of Nageiopsis, to be described later, but the leaves seem to havenbsp;been very deciduous, unlike Nageiopsis, and are at base, when detached,nbsp;somewhat heart-shaped.

Leaves long, slender, slightly narrowed towards the base, which was not seen, and gradually so towards the tip, which is lancet-shaped and subacute, almost acuminate, slightly curved and subfalcate; nerves strong,nbsp;proportionally very remote, parallel, not forking in the parts seen.

The base of this leaf was not seen, and the nerves towards the tip were too obscure to be made out. The plant may be Nageiopsis or Podo-^amites, but the flexuous character of the leaf indicates that it is a Zamites,nbsp;and here I place it provisionally.

Leaves short, oval, acute, abruptly rounded off at base, and showing, when detached, a heart-shaped sinus, almost as broad at base as elsewhere;nbsp;nerves not seen.

Localities: Banks of Dutch Gap Canal; fishing-hut above the canal; road-side near Potomac Run ; near Telegraph Station; rare.

Leaves long, proportionally narrow, subfalcate, acute, widest near the base, abruptly rounded off at base, attachment not seen; nerves not seen.

This is another of the doubtful species of Zamites. The epidermis was so thick that the nerves could not be made out. Only a slightnbsp;striation can be seen. The plant specimen given in PI. LXXXIV, Fig. 13,nbsp;seems to be a tip of a leaf whose base is probably the specimen figured innbsp;PI. LXXXV, Fig. 3. The amount of material obtained from Kankey�snbsp;place is so small and the impressions are so poorly preserved, that thenbsp;number of specimens of any given plant obtained there can not be takennbsp;as indicating its actual abundance or scarcity.

A single fragment of a thick leaf was found at Kankey�s place. The nerves were not seen. It is apparently a portion of a leaf of Zamites toonbsp;imperfectly preserved to permit the species to be determined. .

Leaves pinnate, leaflets oblong, linear-elliptical, obtuse, terminated by several spinous teeth, margins having irregularly placed, shallow, spinousnbsp;teeth; nerves numerous, closely placed, forking one� or more times and atnbsp;varying intervals, slightly diverging, and mostly ending in the teeth, anastomosing occasionally by branches sent off* abruptly from one nerve tonbsp;another.

This curious genus has been found as yet with only one species. It combines the features of Encephalartos with the anastomosing nerves ofnbsp;Ctenis. It is so close to Encephalartos that, were it not for the occasionalnbsp;anastomosis of the nerves, one would have no hesitation in placing it innbsp;that genus. It probably should be regarded as the prototype of that

Leaves and leaflets with the character given for the genus; the shallow, spinous teeth on the margins vary in shape, and tend to pass to rectangular notches; the teeth do not appear on the basal portions of the leaflets ; the base or attachment of the leaflets was not seen; the nerves are numerous, closely placed, fine but distinct; they slightly diverge, fork atnbsp;long intervals and at varying heights throughout the length of the leaf, andnbsp;are approximately parallel; they anastomose rarely by abruptly sendingnbsp;off branches to unite with the adjacent nerve; the anastomosing branchesnbsp;make comparatively large angles with the parent nerve.

This plant evidently varied a good deal in the size of its leaves, for the fragment PI. LXXII, Fig. 4, is much larger than that given in PI.nbsp;LXX, Fig. 4. In PI. LXXI, Fig. 3, the position of the two leaflets indicates that they were disposed in a pinnate manner.

Leaflets variable in size, mostly small, long, linear, comparatively narrow and I�ibbon-shaped, gradually narrowed towards the ends, attached

to the rachis on the upper side and touching each other, or united at base, attached by the entire base, nerves in part forking.

This genus is represented in the Potomac flora doubtfully by one species, which has in some respects a different character from the typical forms, such as Ctenophjllum Brauniamm Schimper.

Leaf very large and wide-spreading; length of leaflets not disclosed, width in the same portion of the leaf variable, ranging from 27�� to 35��;nbsp;leaflets alternate, going off in the lower part of the leaf at a large angle,nbsp;in the upper portion much more oblique, attached by the entire width ofnbsp;the widened base, which is decurrent and meets the expanded base of thenbsp;adjacent ones, forming a broad rounded sinus, those of the upper portion ofnbsp;the leaf united more and more, all curved slightly upwards towards thenbsp;summit of the leaf; tips of the leaflets not seen; nerves very strong,nbsp;going off obliquely at their insertion in the lower and middle portions ofnbsp;the lower leaflets, but nearly at right angles in the upper portions, and allnbsp;turning strongly outwards to enter the leaflets; nerves of the uppermostnbsp;leaflets all oblique; the nerves fork at the insertion or are simple and parallel ; occasionally but rarely those simple at base fopk somewhere higher;nbsp;under a strong lens the nerves are seen to be composed of two closelynbsp;placed nerve-strands which form a flat nerve-bundle.

This splendid plant is very rare; only one specimen was seen. As found in the rock, it was as is depicted in Fig. 2, and probably the specimen depicted in Fig. 3 was attached to the top of it, for it is clearly thenbsp;summit of the specimen given in Fig. 2. But in loosening the imprint innbsp;the quarry it was much broken up. The leaf originally must have beennbsp;of huge dimensions, for the parts seen are clearly but a small portion of it.nbsp;The plant shows an irregularity in the size of the leaflets, for in Fig. 2 thenbsp;right-hand lower leaflet is much wider than the adjacent ones. The midnerve is stoiit and rounded. The leaf must have been over a meter innbsp;length. This species is strikingly like the large Ctempliylla of the Rhaetic

flora of Virginia (see Contributions to the Knowledge of the Older Mesozoic Flora of Virginia, Mon. U. S. Geol. Survey, vol. 6, PI. XXXIX, Figs. 1-3,nbsp;to PI. XLII, Fig. 1). It may possibly be a descendant of some such plantnbsp;as G. grandifolimn. Its extreme rarity indicates that this form of cycadnbsp;was nearly extinct in this region.

Leaves pinnate, with leaflets Ungulate or elliptical in shape, obtuse at the summit, inserted on the upper face of tlie midrib by a contracted base,nbsp;equilateral; nerves fine, branching dichotomously, diverging slightly fromnbsp;the point of attachment towards the borders of the leaflets, which arenbsp;always entire.

This description of the genus given by Saporta coincides exactly with the character of a fossil found in the Potomac flora. Only one speciesnbsp;of the genus was found. The genus is characteristic of the Lower Cretaceous, and seems to play a very unimportant part in the Potomac flora.

Leaf pinnate, midrib slender ; leaflets alternate, diminishing in size in ascending, distant, oblong, linguiform, slightly curved upwards, attachednbsp;to the upper surface of the midrib by a rounded, abruptly narrowed base,nbsp;which in the lower ones is slightly auriculate, obtuse; nerves fine, numei'-ous, closely placed, diverging slightly from the point of attachment, andnbsp;ending, except the central ones, in the entire margin; outer nerves simplenbsp;or deeply furcate ; inner ones I�epeatedly forked, with the ultimate branchesnbsp;of all very long and approximately parallel.

Only one specimen of this very fine plant was found, and that in a fragmentary condition. The leaflets of the lower portion have a basenbsp;which indicates that they were attached by a callosity. The nerves whennbsp;forked have very long branches, owing to the distance from their ends atnbsp;which the forking takes place. It is very much like Schenk�s Podosamites

Zitteli {Olossozamites Zitteli Schimper)/ but the leaflets are not so obtuse and are farther apart, while the nerves are more branched.

Leaf profoundly pinnatifid; rachis thick, striated, and furrowed ; leaflets or lacinise approximate, linear-elongate, entire, enlarged at base, separated by an acute sinus; nerves equal, thick, arising from the rachis,nbsp;diverging towards the base, then approximate, parallel, forked, branchesnbsp;uniting to form areolae that are obliquely elongate, rhomboidal in shape.

The above is Zigno�s description of Ctenis, being an amendment of that of Lindley and Hutton. If we alter this so as to read �leaves pinnate,� and omit the items �enlai'ged at base, separated by an acute sinus,�nbsp;it will apply to a very noteworthy form found in the Potomac flora. Thisnbsp;is without doubt either a true Ctenis, or so closely allied to it that, in thenbsp;absence of more definite characters, it may be placed in that genus.

Leaf very large, pinnate; leaflets attached by the entire base, which is narrowed and rounded off on both sides, to the upper face of the midribnbsp;or stem, obtuse at their tips and rounded, with broad, shallow, seemingnbsp;lobes on the under side, imbricated some distance above the base, eachnbsp;leaflet expanding at that point and partly overlapping the next one; nervesnbsp;strong and distinct, wide apart, forking at or near the base or a shortnbsp;distance higher up; branches, so far as seen, parallel, anastomosing atnbsp;long intervals by a few inosculating branches, so as to form long irregularnbsp;or subrhombic meshes, uppermost leaflets united; leaf terminating in anbsp;leaflet in which the midnerve seems to split up into two branches; at thenbsp;tips of the leaflets the anastomosis is more copious and the nerves are finernbsp;and more closely placed.

This remarkable plant agrees quite well with the .subgenus Ctenis, and in some points it is like the figures of Ctenis falcata^ Lindley and Hutton,

g-Iven by Zigno. It has the same mode of insertion of the nerves, which are irregular, forking, and anastomosing, but in Ctenis falcata the leafletsnbsp;are decurrent, and become much widened at their insertions. The Potomacnbsp;plant is more like Nathorst�s plant from the Rhmtic of Sweden, which henbsp;first named Anthrophyopsis Nilssoni, and afterwards called Ctenis fallaxnbsp;The termination, especially of the leaflets in the two plants, shows a resemblance. PI. CXXXVIII, Fig. 12, gives what seems to he the middle of anbsp;leaf of large size. Fig. 11 gives the upper portion of a leaf that seems tonbsp;have been much larger than that depicted in Fig. 12, as is shown in thenbsp;much greater width of the midrib. This specimen is a good deal distortednbsp;by pressure, so that its true character may be disguised. The wide midribnbsp;seems to be split into two branches, which ai�e connected by smaller nerves.nbsp;The fragment of a leaflet visible on its left-hand side seems to have had itsnbsp;base pressed over upon the upper surface of the midrib, while the lowernbsp;half of that on the right hand seems to have been torn away by thenbsp;splitting off and detaching of a portion of the midrib. The specimennbsp;given in Fig. 10 seems to be the tip of a leaflet, perhaps corresponding tonbsp;the basal portions shown in Fig. 12.

Leaves small, with a slender rachis, pinnate; leaflets alternate, remote, directed more or less upward, with a gradually narrowed base, often furnished with a short petiole, ovate-elliptical, elongate, lancet-shaped, ornbsp;linear, sometimes somewhat curved, detaching themselves from the rachis,nbsp;and usually found isolated; nerves forked at the base, often very fine andnbsp;closely placed, parallel with the margin to near the tips of the leaflets,nbsp;where they converge.

The genus Podozamites is represented in the Potomac flora apparently by a considerable number of species; but as the specimens appear usuallynbsp;in the form of fragmentary and detached leaves, they do not generallynbsp;admit of a full characterization and positive determination. The leafletsnbsp;having the character of Podozamiies are quite rare, and the genus contributes no important element to the flora. They give one the impressionnbsp;of a type in decadence. Most of them are in form strikingly like the

leaves of Nageiopsis, a genus of conifers described in this work, but they differ from this in the very deciduous nature of the leaflets, and above allnbsp;in tlie convergence of the nerves at their summit.

Leaves unknown; leaflets suhfalcate, narrowly elliptical to strap-shaped, obtuse or subacute, gradually narrowed to the base so as to form a broad,nbsp;short pedicel, thick and leatlieiy; nerves slender, and not well disclosed,nbsp;forking near the base, then nearly parallel to near the tips, where they converge.

Only detached fragments of leaflets were found. The leaflets must have varied a good deal in size, as PI. LXVIIT, Fig. 6, represents a nearlynbsp;complete leaf, which is much smaller than that of which PI. CLXX, Fig. 9,nbsp;represents a fragment. The shorter form, PI. LXVIII, Fig. 6, is a goodnbsp;deal like Zamites ovahis, and Z. affinis Schenk,^ forms which Scliimper makesnbsp;Podozamite.s. The longer leaflet on the other hand is somewhat like Z.nbsp;nervosus Schenk, same plate. Fig. 10.

Plate LXXIX, Pig. ,5; Plate LXXXII, Pig. 4; Plate LXXXIII, Figs. 1, 2, 6, 7; Plate LXXXIV, Pigs.

Leaves comparatively large, pinnate ; leaflets large, elongate-elliptical in form, varying a good deal in size, maximum width varying from 27�� tonbsp;40��, usually comparatively broad, full length not seen, hut ranging fromnbsp;11�� to over 14��, obtuse or subacute at tip, usually somewhat narrowednbsp;toward the base, and at the base rather abruptly rounded off into a shortnbsp;pedicel; nerves strong, quite remote, forking at or near the base, and thennbsp;parallel to near the tip, where they converge and connive more or less.

Localities: Road-side near Potomac Run; Fredericksburg; near Telegraph Station; rare.

This is the most common Podosamites, but still it is not abundant. More specimens were found at Fredericksburg than anywhere else, prob-

ably because more material was obtained there than at most places. PI. LXXXIIT, Fig. 1, gives the upper portion of an unusually large leaflet, innbsp;which the nerves are obscure, but may be seen to converge at the summit.nbsp;Fig. 2 of the same plate shows two leaves of medium size in a position asnbsp;if coming otf from a common stem. PL LXXXIV, Fig. 10, gives threenbsp;leaflets detached, and from displacements overlapping one another. Figs.nbsp;14 and 15 of the same plate give the base and the tip of the leaf fragmentsnbsp;slightly enlarged, to show the nervation. The base given in Fig. 14 isnbsp;more abruptly rounded off than usual, but little naiTowing toward the basenbsp;having taken place; possibly such leaflets, with those such as given in Fig.nbsp;8 of the same plate, may belong to a different species.

This Fodozamites does not seem to be near any of the heretofore described species. �

Leaves not seen; leaflets large and long, length not fully disclosed maximum width varying from 26�� to 35��; shape probably oblong to elongate-elliptical, gradually narrowed to the base, and elliptically shaped there,nbsp;furnished with a long, broad pedicel, curved to one side, deciduous; nerves,nbsp;forking near the base, then nearly parallel, tips of leaflets not seen.

This possibly may be a Nageiopsis, as the nerves at the tips of the leaflets were not seen, but the deciduous nature of the leaflets indicatesnbsp;that they belong to Fodozamites.

Leaflets very large, 4.5�� wide and over 20�� long; shape not seen, probably elongate-elliptical, with stout pedicel at base; nerves where seennbsp;strong, parallel, remote, composed of two nerve-strands which are closelynbsp;placed, and form a flat nerve-bundle.

This plant is quite rare., and, owing to their great size, the leaflets were found only in a fragmentary condition; hence their shape could not be made

out exactly. PI. LXXXIII, Fig. 5, from the Potomac Run locality, indicates that it had at the base of the leaflets a stout pedicel. PI. LXXXII, Fig. 2, from Fredericksburg, is a fragment of what must have been a verynbsp;large leaf. The lower or posterior margin of this leaf is nowhere shown.

Plate LXXX, Fig. 6; Plate LXXXV, Figs. 10, 15; Plato LXXXVII, Fig. 1; Plate CLXX, Fig. a.

Leaves very deciduous, varying in length, oblong, subacuminate, maintaining the maximum width to near the base, and then suddenly rounded off and attached by a short pedicel; nerves branching near the base, andnbsp;one branch sometimes forking again higher up; at the tips of the leafletsnbsp;the nerves converge to a common point, quite distinct.

Localities : Fishing-hut above Dutch Gap Canal; Deep Bottom ; near Telegraph Station ; road-side near Potomac Run ; bank near Brooke; rare.

The leaves of this plant are much like those of Poclozamites lanceolatus Schimper, and the larger leaves resemble Poclomniites Emmonsi Newberry.nbsp;The smaller ones resemble P. tenuinervis.

I take this opportunity to correct an oversight made in Contributions to the Knowledge of the Older Mesozoic Flora of Virginia (Mon. U. S. Geol.nbsp;Survey, vol. 6) with reference to the employment of the name Podozamitesnbsp;Emmonsi. This name I used for a Podozamites found by Emmons in thenbsp;Rhietic of North Carolina, overlooking the fact that Professor Newberrynbsp;had already used this name for the same plant in his article on the Chinesenbsp;Mesozoic plants in Smithsonian Contributions to Knowledge.

Leaves quite large, with strong rachis; leaflets attached on the upper side of this by the whole width of the base, sometimes expanded at base sonbsp;as to extend up and down the rachis, linear-lanceolate or elongate-linear,nbsp;acute at tips, of firm leathery consistency; nerves simple and parallel.

This description of Schimper given to the genus agrees exactly with certain forms that are very common in tlie Potomac flora. The plantsnbsp;placed in the genus Bioonites are by far the most abundant cycads in the

Potomac strata, and these alone give to this group of plants the considerable importance that they possess in this flora.

Vterophyllum Buclnanum, Efctingshausen, Beitrage z. El. dev Wealdetiperiode, p. 21, PI. I, Fig. 1.

Fterophyllum Saxonimtm, Reich., Ettiiig.shausou, Kreideflova vou Niederschooaa, PI. I, Figs. 11, 12.

Plate LXVIII, Fig. 1; Plato LXTX, Fig.s. 1, 3; Plate LXX, Figs. 2, 3; Plate LXXI, Fig. 1; Plate LXXII, Figs. 1, 2; Plate LXXIII, Pigs. 1-3; Plate LXXIV, Figs. 1-3.

Leaves very large, attaining probably the length of a meter and over; maximum width, 30�� and over; rachis stout, showing a keel on the undernbsp;side ; epidermis over the rachis and leaflets thick and durable ; leaves thicknbsp;and leathery; leaflets varying much in dimensions, distance, shape, andnbsp;termination; leaflets linear-acute, sometimes closely placed, sometimesnbsp;remote, those in the middle part of the leaf the most commonly found,nbsp;these going off at an angle of 45�, those of the upper part more and morenbsp;oblique, until at the summit they occur in the prolongation of the midrib, and the leaf is terminated by a leaflet, the terminal leaflets muchnbsp;shorter and narrower than those lower down ; length varying, attaining innbsp;some cases 25��; the leaflets slightly narrowed to the base and attached bynbsp;the whole width of the base, obliquely set on and decurrent; epidermisnbsp;sometimes showing a granulation or a line of dots between the nerves;nbsp;nerves fine, very closely placed, forking at the base, parallel, and terminating without convergence in the summits of the leaflets, some of the outernbsp;ones ending in the margins a little below the summit.

Localities: All points on James River that yield plants, except Deep Bottom; especially abundant at entrance to Trent�s Reach, in banks ofnbsp;Dutch Grap Canal, and at fishing-hut above the canal; very abundant atnbsp;Kankey�s; found also at all plant localities north of Kankey�s to Fortnbsp;Washington, but not abundant beyond Telegraph Station.

This splendid plant is one of the most widely difFused and characteristic fossils of the Potomac flora. At the entrance to Trent�s Reach, in the thin plant-bearing layer near the top of the blufiP, the imprints are in placesnbsp;very numerous, and much of the plant-substance is still retained, the relicsnbsp;being matted together. Here it is found in company with Baieropsis

phiripartita, Brachypliylluyn, Frenelopsis parceramosa, etc. In the right hank of Dutch Gap Canal, in the thin partings of dark gray clay, interstratifiednbsp;with sandy layers, very large impressions occur and the fossils are verynbsp;numerous. They seem to occur irregularly distributed and in pockets.nbsp;Some of the imprints seen lying in the clay were 12 to 18 inches long andnbsp;as wide, but owing to the brittleness of the rock they were much brokennbsp;in taking them out. At a spot about 200 yards above the fishing-hut atnbsp;Dutch Gap, where hardly any other fossil occurs, the leaves of this plantnbsp;are so abundant as to fill the clay for the thickness of a foot or more. Itnbsp;is a curious fact that at this point, and at several localities north of Fredericksburg, if the remains of this plant occur in great numbers in thenbsp;clay, they seem to exclude others. The distribution is apparently somewhat peculiar. On leaving J ames River not a trace of the plant is to benbsp;seen until Kankey�s place is reached. Here immense numbers of thenbsp;leaves occur in the dark clay with hardly any other plants. None werenbsp;found at Fredericksburg, and as the amount of material obtained therenbsp;was large, we may safel)^ assume that it did not exist at that locality. Itnbsp;occurs as the principal fossil in the cut where the railroad crosses thenbsp;Occoquan. It is abundant near Telegraph Station, but only fragmentsnbsp;occur at White House and at Fort Washington. It has not been certainly identified north of Fort Washington. Some small bits of leavesnbsp;found at Baltimore, on Belt and Covington streets, seem to belong to thisnbsp;species, but they can not be certainly identified. It was indicated bynbsp;fragments found in the excavation for the reservoir at Washington.

Ettingshausen, in his Beitrag zur Flora der Wealden Periode, described this plant under the name Pterophyllum Buchianum, as occurring in the Wernsdorf strata of the northern Carpathians, considering thesenbsp;as of Wealden age. He gives a figure of a fragment belonging, as henbsp;thought, to a cycad leaf three or four feet long. Schenk (Die foss. Pflan-zen der Wernsdorf-Schichten) shows that these strata, according to thenbsp;investigations of Hohenegger and Zittel, are not Wealden but Urgoniannbsp;in age, younger than the oldest Neocomian, and older than the Gault. Itnbsp;is very fortunate that the Potomac formation has yielded so many finenbsp;specimens of this plant, as they add a good deal to our knowledge of it.

All the parts are shown except the base of the leaves. Among the hundreds of specimens seen, it is singular that in no case was any portion of the base found.

The leaves appear to have been thick and durable, for in a number of cases the leaf-substance may be stripped from the stone, retaining the shapenbsp;of the leaflets. The epidermis seems to be especially thick over the midrib. The nerves are immersed in the leaf-substance and are usuallynbsp;obscured.

In Ettingshausen�s figure the specimen is somewhat distorted by pressure. The leaflets on the right-hand side have been crushed over at base so as to appear to be attached to the upper face of the midrib and partlynbsp;within its margin, whereas they are really attached to the margin and lienbsp;usually in one plane.

This plant seems not to have been confined strictly to the Urgonian, but to have survived to a later period, while its narrower form at leastnbsp;began in the Wealden. Ettingshausen ^ gives figures of Pterophyllum Sax-onicum Reich., which certainly represent portions of D. Buchicmus. Innbsp;these figures some of the leaflets go off at a more open angle than is usualnbsp;in D. BucManus, but this is due to distortion from pressure, for this mode ofnbsp;departure can be duplicated in many of the Potomac plants. Ettingshau-sen says that the surface of the Niederschoena plant is covered with finenbsp;dots arranged in rows between the nerves. In the Potomac plants theynbsp;are closer than Ettingshausen�s figure represents them to be. Hosius andnbsp;Von der Marck^ represent a fragment which they identify correctly withnbsp;Bteropliyllmn Saxonimm, coming from the Neocomian sandstone of the Teu-terburger Wald. This is evidently a portion of the midrib and the basesnbsp;of two leaflets of Dioonites Buchianm. The leaflets are by distortion fromnbsp;pressure made to go off nearly at right angles.

Leaves long and wide, with a stout midrib; leaflets subopposite, inserted on the upper face of the midrib and considerably within its mar-

gin, very remote, obtusely rounded off at the tips, comparatively short, bases of the leaflets thickened and callous when torn off, and when thenbsp;midrib is compressed, leaving a depressed scar.

The figure gives a portion only of the large specimen found. The specimen is 20�� long, and shows no decided diminution in the size of thenbsp;midrib or in the lengths of the leaflets ; but the leaflets at the summit ofnbsp;the stem are only half as far apart as those at bottom; seventeen leafletsnbsp;occurred on the portion found.

Pterophyllum dbietiniim G�pp., Duuker. Mon. der norddeutscli. Wealdenbild., PI. VII, Fig. 2.

Dioonitcn aiietinus Miquel, Schenk. Flor. der nordwestdeutsch. Wealdenform., PI. XVI, Fig. 1.

Leaflets and nerves as in the normal form B. BucManus, except that they are much narrower in the lower parts of the leaves.

Localities: Dutch Gap, especially at the fishing-hut above the canal; Kankey�s; crossing of the Occoquan; near Telegraph Station.

These leaflets, as those of the normal species, vary a good deal in the distances apart at which they are placed. In PI. LXVII, Fig. 6, they arenbsp;very remote; in PI. LXXI, Fig. 2, they are very close together. Thenbsp;forms that are placed in this variety show throughout the leaf narrow leaflets, and they do not seem to be mere accidentally narrow forms of thenbsp;typical plant. The}^ never graduate into the wider leaf forms.

This narrow leaf variety seems to be the same with theWealden plant figured by Schenk as Dioonites ahietinus Miquel, in his Wealden flora, PI.nbsp;XVI, Fig. 1. It appears also to be identical with the fossil given by Dun-ker as Pteropliyllum abietinum G�pp. Hosius and Von der Marck^ give anbsp;figure of what they call D. ahietinus, which is exactly like some of thenbsp;specimens of this Potomac fossil. The figure of the Westphalian fossilnbsp;represents a plant distorted by pressure. It comes from the Neocomiannbsp;sandstone of the Teuterburger Wald.

Tlie speciineus of this variety are much rarer than those of the normal species D. Biichianm.

Tliis form, if identical with the European fossils named above, begins in the Wealden and survives into the Neocomian.

dVunks varying considerably in shape and in dimensions, petrified with silica, more or less flattened, seen with the broader side in front, tliey arenbsp;oblong-ovate and truncate; in cross-section they are broadly subelliptical;nbsp;medulla proportionally small; woody cylinder comparatively thick; cortical exterior layer, with the permanent bases of tlie petioles very thick;nbsp;bases of the petioles in cross-section normally subrhombic or subtriangular,nbsp;with the lower angle very obtuse, the outer angles acute and prolonged, thenbsp;superior side forming a curved line bent upwards or forming an obtusenbsp;angle, but often from pressure distorted into irregular, rhombic, or triangular forms; trunks each with a large eccentric terminal leaf-bud or growingnbsp;bud; some of the trunks, probably of female plants, have numerous lateralnbsp;buds; others, probably male plants, are without lateral buds; bases of thenbsp;petioles of the leaves represented by open casts of the petioles, which fromnbsp;the points of insertion of the petioles pass upwards and outwards, so thatnbsp;their direction at their exit from the cortical investment is nearly horizontal.

These trunks have some of the characters of Carruthers�s genus Bennett-ites and of MantelUa Brongn., being apparently an intermediate type. I have named the genus in honor of Mr. Tyson, who first called attentionnbsp;to these plants. Carruthers� says: �Through the kindness of Principalnbsp;Dawson I have seen a photograph of one of the cycadeau stems found bynbsp;P. Tyson, esq., in Maryland. *nbsp;nbsp;nbsp;nbsp;*nbsp;nbsp;nbsp;nbsp;^ It is obviously a species of

It seems from his description of the plant that Carruthers saw a photograph of trunk No. 1. He does not seem to have had a photographnbsp;of trunk No. 2, which differs in important points from No. 1. Carruthersnbsp;tliirdcs that the apparent buds on his Bennettites are not leaf-buds, butnbsp;organs of reproduction. There is nothing in the Potomac plants to show

' Fossil cycadean stems from the secondary rocks of Britain, Trans. Linn. Soc. Loudon, vol. 2�, ISrO,

what the nature of the buds was. Carruthers�s description of the cross-section of the bases of the petiole of Bennettites agrees well with the cross-sections in Tysonia. He explains the exterior aspect of the trunks, which shows a series of hollow imprints left by the bases of the petioles separatednbsp;by plates, as caused by certain processes which seem to have taken place innbsp;the Potomac plant also. He says the trunk, when living, was surroundednbsp;by the permanent bases of the petioles, and the base of each petiole wasnbsp;clothed with a dense ramentum, which was developed to such an extent asnbsp;to separate very considerably each petiole from its neighbor. The silicanbsp;forming the petrifying material having found speedy access to the delicatenbsp;scales of the ramentum has preserved them in a remarkably perfect manner'nbsp;In some of the English specimens the petrified ramentum stands out as anbsp;net-work of ridges, while the originally, more durable petioles have decayednbsp;and left rhomboidal cavities representing their original form. Carruthersnbsp;states also that the leaf disarticulated at a point some distance from thenbsp;cortex, leaving a considerable portion of the bases of the petioles permanently surrounding the stem. This explanation given for the Englishnbsp;Bennetites no doubt applies to the similar features seen fn the Potomacnbsp;Tysonia. In this latter, now thoroughly silicified in all the specimens seen,nbsp;it is clear that the material surrounding the bases of the petioles was silicifiednbsp;before the bases, and that these subsequently decayed, leaving perfectnbsp;hollow casts of their form.

No microscopic examination of the trunks of Tysonia has been made, and I am compelled to confine the description to macroscopic characters.

There are two kinds of trunks, differing mainly in the presence or absence of axillary buds There are two kinds of axillary buds on thenbsp;same trunk, a feature which, according to Carruthers, appears in Mantellianbsp;but not in Bennettites. In would seem that in the buds on Tysonia, whichnbsp;resemble those of Bennettites, there was a woody axis of varying size,nbsp;surrounded by scars of leaves much smaller than the normal ones, or ofnbsp;bracts. This woody axis certainly protruded beyond the bases of thenbsp;petioles. Some of them are larger than others and some are hollow, thenbsp;hollows being no doubt due to decay before silification. No indication ofnbsp;fructification has been seen in connection with the Potomac stems.

These stems have a number of features in common with Bennettites, but do not fully agree with that genus. Compared with Mantellia Brongn.,nbsp;Cycadeoidea, Buckland, they show some points of resemblance. Carruthersnbsp;says of Mantellia trunks that they are cylindrical, covered with the longnbsp;permanent bases of the petioles, and have the fruits borne on secondarynbsp;axes which generally protrude beyond the bases of the petioles. In thisnbsp;feature these secondary axes resemble Tysonia^ and not, according tonbsp;Carruthers, Bennettites. The axillary branches in Mantellia, like those ofnbsp;Tysonia, are broken off at the point where they leave the bases of thenbsp;petioles. Carruthers says that some of the branches in Mantellia arenbsp;undeveloped and still exist as unexpanded leaf-buds; and this seems to benbsp;the case with some of those of Tysonia, those that have little or no woodynbsp;axis. Some of the stems of Mantellia have no lateral buds, and they may,nbsp;as Carruthers says, be male stems, their staminal flowers being on conesnbsp;borne on the termination of the main axis. The Potomac stem No. 2 hasnbsp;no axillary buds, and shows indications of having borne a terminal appendage (bud!) by the side of the terminal growing leaf-bud. Carruthersnbsp;says that the Mantellia trunks were cylindrical, their flattened conditionnbsp;being due to pressure.

From this it will be seen that the stems of Tysonia have a number of points in common with Mantellia. They stand nearer to this than tonbsp;Bennettites. The shape of the trunk is more that of Bennettites, but in thenbsp;shape of the bases of the petioles and in other features Tysonia morenbsp;closely resembles Mantellia.

In describing the new species Tysonia Marylandica, it is best to notice the two nearly complete stems separately, as they are typical and shownbsp;some important points of difference. I will describe them as trunk No. 1nbsp;and trunk No. 2. One of these was found, as stated before, near Contee�snbsp;station, in an iron-ore pit near the base of the Variegated Clay formation,nbsp;and one was found on a farm near Beltsville, a locality a few miles southnbsp;of Contee�s. A fragment like trunk No. 1 was found with this trunk, andnbsp;another fragment like trunk No. 2 was found on the surface of the Variegated Clay group at a locality (Spring Glarden) in the outskirts of Baltimore. It is impossible now to tell which of the trunks was found near

Contee�s. The fragments in all respects resemble the ti�unks. This would indicate that the differences seen in the trunks are constant and not merelynbsp;accidental, and hence have an important meaning.

This trunk is silicified, of an ash-gray color, and is free from ferruginous matter. It is oblong-elliptical in shape, with a cross-section roughly elliptical in form, as shown in PL CLXXVIII, which giv^es a photograph of its top. The flattening may be due to compression. From onenbsp;side near the base a considerable portion has been broken off, as is shownnbsp;in PI. CLXXVI. The maximum height of the trunk, measured on thenbsp;the perfect side, seen in PI. CLXXIV, is 3T�, and the greatest dimensionnbsp;at base is 30��. Its thickness there is 26��. The length of the longestnbsp;dimension at top is 19��, and the maximum width there is 12��.

At the top a portion is broken away so as to produce a depression slanting downwards, well shown in PI. CLXXVI. This looks a good dealnbsp;like the scar that would be left by the tearing away of a terminal stem-likenbsp;appendage. This depression occurs on one side of the summit of thenbsp;trunk. What was probably the terminal bud of growth is distinct fromnbsp;this, and is seen in the center of the top on PI. CLXXVIII as a rathernbsp;faintly marked depression. On the summit, and to the left of the centi�alnbsp;bud, is another large depression, which appears to correspond to a terminalnbsp;growth or bud of some kind. Plate CLXXV gives a photograph view ofnbsp;the perfect narrow side of the trunk in question, giving an idea of its thickness. Plate CLXXVII gives a view of the base of the stem, showing thenbsp;small central medulla surrounded by a comparatively thick woody zone, anbsp;vaguely defined cortical layer, and outside of all the very thick mass, composed of the bases of the petioles and the material wTich enveloped themnbsp;This last portion makes up much the larger part of the trunk.

On the surface of the trunk, well shown on PI CLXXIV, are several large, deep, irregularly shaped pits, due no doubt to the decay of severalnbsp;adjacent bases of petioles before the silicification took place.

The bud-scars are of two kinds, which are well shown on the plate last mentioned. The large scars stand out somewhat from the surface ofnbsp;the trunk, and have a woody axis of varying thickness, surrounded by onenbsp;or more concentric circles of small leaf-scars. These leaf-scars are aboutnbsp;one-third the size of the imprints left by the bases of the petioles. Thenbsp;woody axis within these encircling small leaf-scars varies a good deal innbsp;size, and some of them, as Carruthers pointed out, are more or less hollow,nbsp;no doubt being caused by tlie decay of the axis before silicification tooknbsp;place. These axes probably bore some kind of fructification.

The small leaf scars surrounding these axes were probably caused by leaves of small size or bracts, whose bases, like those of tlie larger leaves,nbsp;persisted until^after the silicification of the-material which surrounded themnbsp;took place and then decayed. The smaller bud-scars are quite differentnbsp;from those just described. These too may be seen on PI. CLXXIV.nbsp;Tliey are considerably smaller than those witli the woody axes, and consist simply of concentric circles of small leaf-scars like those around thenbsp;woody cores of the larger scars. They have no woody axis, and appearnbsp;to be undeveloped buds composed of small leaves or bracts. There isnbsp;nothing to show what is the functional meaning of these numerous scars ofnbsp;buds, but it is quite possible that the larger ones may have borne thenbsp;female inflorescence, and hence trunks such as No. 1 would belong to thenbsp;female plants. The open pits left by the decay of the bases of the petiolesnbsp;of the principal leaves of the trunks are exact casts of these bases. Theynbsp;seem to have had normally in cross-section a shape that is accurately represented by a bow with the string bent into an acute angle caused bynbsp;drawing an arrow to its head, the curving bow representing the upper sidenbsp;of the hollow cast. Owing to distortion they assume sometimes rhombicnbsp;or elongated triangular shapes. They are smaller towards the top of thenbsp;stem than towards the bottom, and have an average size towards the bottom of the trunks of 18�� by 8��, towards the top of 10�� by 5��.

Between Washington and Baltimore was found a large fragment exactl}- resembling trunk No. 1, but not broken off from that. This resem-

blance may indicate that trunk No. 1 came from the same locality. It is silicified in the same way and has the same kinds of scars. The casts ofnbsp;the petioles in this fragment are rather larger than those of trunk No. 1,nbsp;being 22�'� by 12�� in cross-section. This fragment is shaped like annbsp;irregular disk or quoit, having the dimensions 26�� by 19quot;�.

This was probably obtained from near Beltsville, being picked up on the surface of the ground on Mr. Emack�s farm. It is exactly like the fragment found at Spring Garden, Baltimore, being even silicified in the samenbsp;way. The silica, replacing the vegetable matter of this trunk, contains anbsp;large amount of iron, so that in proportion to bulk it is much heavier thannbsp;trunk No. 1. Curiously enough, both this trunk and the ferruginous fragment found at Spring Garden show a projecting seam of ferruginous silica.nbsp;This is shown on the narrower side of the trunk on PI. CLXXX, andnbsp;less distinctly on the front left-hand side, on PI. CLXXIX. This seamnbsp;appears to be due to a crack in the trunk, which was filled with infiltrated silica in the form of a vein. This silica in the projecting plate ornbsp;vein seems to be in part at least due to a partial filling of the crack bynbsp;sand, for grains of sand are mixed with the silica deposited from solution.nbsp;On one side of the trunk near the top and close to the projecting siliciousnbsp;plate, soldered to it and the trunk, are a number of small pebbles coatednbsp;with iron. The sand and pebbles indicate that the original place of thenbsp;trunk was in sandstone, not clay, and this would cause us to infer that thenbsp;trunk was silicified in the lower Potomac sand. It would then come intonbsp;the upper Potomac or clay member only after the destruction of the sandstone or sand originally holding it. Trunk No. 2 is ovate in shape, andnbsp;decidedly narrowed towards the top. It is not so much flattened as No.nbsp;1, as is indicated in the view of the narrow side given in PI. CLXXX. Anbsp;small piece is broken away from one side at the top, but still this trunknbsp;is more complete than No. 1. On the broader side, PI. CLXXIX, thenbsp;maximum height is 41quot;�, the greatest dimensions at base 35quot;�, the shorternbsp;dimension there 34quot;quot;�. The dimensions at the top before the breaking off of

the fragment were 14'�� by nbsp;nbsp;nbsp;The tapering to the top is caused mainly

by a slope of one face of the trunk, viz, that shown on the right-hand side on PI. CLXXIX, and hence the terminal bud, or that of growth, isnbsp;thrown much to one side of the axis of the trunk. A large terminal budnbsp;may be seen on the highest part of the trunk, and on one side of this isnbsp;the break spoken of, which slopes down the trunk just as if the base of anbsp;stem had been torn off. It is quite possible that this may have been anbsp;stalk bearing the male inflorescence. If so, the trunk would be that of tlienbsp;male plant, and the structural differences from those of No. 1 would benbsp;accounted for by the sexual distinction.

In both No. 1 and No. 2 the growth seems to have been maintained by the development of successive circles of leaves at the summit of thenbsp;trunk which unfolded from a bud composed of undeveloped leaves, andnbsp;not from a terminal bud inclosed by bud scales, as Saporta holds to be thenbsp;case with his genus Clatliropodiwn. The fracture may be seen on PI.nbsp;CLXXIX, near the top of the trunk on the left hand, and very distinctlynbsp;on PI. CLXXX in front near the top. Trunk No. 2 shows none of thenbsp;larger lateral or axillary growths or buds such as are so common in No. 1.nbsp;Near the top are faint indications of what may have been two small undeveloped leaf-buds without woody axis, but they are too obscure for us tonbsp;conclude positively that they are buds of any kind. They are composednbsp;of circles of very minute apparent leaf-scars, which are much smaller thannbsp;those similarly placed in No. 1 and not near so distinct as these.

The hollow casts left by the bases of the petioles indicate that these had normally, in cross-section, the same shape as those of trunk No. 1.nbsp;But there is a greater tendency than in No. 1 for the upper side to be bentnbsp;in the form of an angle and thus give the cross-section a rhombic shape.nbsp;Some of the imprints are a good deal larger than the others, but the variations are due to distortions from pressure. The average dimensions of thenbsp;cross-sections are 22�� by 12��.

This specimen, found at Spring Garden, measures in its greatest length 27��, and in its greatest width 23'��, being in the shape of an irregular prism

It seems to have been split off long-itudinally from a trunk so as not to show any portion of the terminal bud. It has no axillary buds. Thenbsp;cross-sections of the bases of the petioles resemble those of No. 2, butnbsp;are somewhat higher proportionally, being 14�� in height, against onlynbsp;20�� in length.

We may from the above detailed account sum up the description of the species as follows :

Stems ovate or oblong, more or less flattened, medulla comparatively small; woody zone large, external integument, with the bases of thenbsp;petioles, very thick; male inflorescence probably borne on a stalk on thenbsp;summit of the trunk by the side of the bud of growth of the trunk, andnbsp;carried on a trunk without axillary buds; female inflorescence on axillarynbsp;growths; growth of the trunk maintained by a terminal bud, which unfolded successive circles of leaves.

Localities all in Maryland, viz: Spring Garden, at Baltimore; near Contee�s station; near Beltsville.

The conifers form the most important element in the Potomac flora. Taken as a whole they lend a decidedly ancient aspect to this flora Anbsp;number of the most important of these conifers have passed entirelynbsp;away, leaving no living species. The genera still surviving and mostnbsp;nearly allied to these more important Potomac forms appear now verynbsp;locally distributed and contain few species. Indeed we may regard themnbsp;as in process of extinction. Such of them as have hitherto been found innbsp;other parts of the world are here much more abundantly represented.

The conifers are largely developed in variety of types and in the number of individuals belonging to the different types, as well as in thenbsp;very general diffusion of the forms. In the number of different speciesnbsp;the conifers are inferior to the ferns, but they far surpass the ferns in thenbsp;number of individuals belonging to each species. They are much morenbsp;MON XV-13

generally diffused than are most of the species of ferns. When a species of fern is found it is always, except on Potomac Run, among the rarest ofnbsp;the plants. At the same time the different species of ferns are usuallynbsp;very restricted in occurrence. The conifers form the most widely diffusednbsp;of the Potomac plants, and when they occur they are generally the mostnbsp;abundant plants at the locality. One or two examples may be given tonbsp;illustrate the abundance of individuals. At the entrance of Trent�s Reach,nbsp;in one layer six to eight inches thick, fragments of the branchlets ofnbsp;Fenelopsis parceramosa were so abundant, that they formed a considerablenbsp;portion of the mass of the stratum. With these immense numbers ofnbsp;fragments of Baieropsis pleuripartita were found. Fenelopsis ramosissima isnbsp;by far the most common plant at Fredericksburg.

The abundance of imprints of the leaves of conifers is not the only evidence of the great development of conifers in the Potomac. It is shownnbsp;in the immense amount of lignite formed from coniferous wood. Thisnbsp;lignite occurs both in the form of isolated logs and fragments, and in tiersnbsp;of logs piled one over the other, as if caused by prostrate forests, indicating that some, at least, of the conifers of that day grew massed in forestsnbsp;as now.

Certain peculiar genera, now extinct, seem to have been very largely developed in the Potomac vegetation, and if we are to judge from theirnbsp;predominance in the fossils of localities where they occur, they must havenbsp;formed the leading and most characteristic types. These will be noticednbsp;further on under proper heads. The archaic clwacter of many conifersnbsp;as well as ferns does not prepare us to expect to find angiosperms associated with these two elements.

Trees or shrubs with leaves and branches spreading in one plane; leaves varying much in size and shape, those towards the base of the twigsnbsp;sometimes smaller than those higher up, distichous mostly, or rarely sub-distichous, opposite and persistent, attached by a short slightly twistednbsp;footstalk, usually to the side of the twig, more rarely slightly within the

margin on the upper or under surface of the stem, either attenuated towards the base or abruptlv rounded off there, at their ends acute ornbsp;subacute; nerves several, coalescing at base to form a footstalk, forkingnbsp;immediately at the base or a short distance above, then approximatelynbsp;parallel to near the tips of the leaves, where they are somewhat crowdednbsp;together, but do not converge to a union, ending in or near the extremity.

This fine genus is one of the most largely developed and characteristic forms of the Potomac flora, fuimishing a very important and widely diffusednbsp;type. The single leaves and unbranched leafy twigs are so much like thenbsp;cycad genus Fodozamites, that when the}^ were first found I took them tonbsp;be forms of that genus, but later so many specimens were found showingnbsp;unquestionable coniferous characters, that I found myself, contrary to mynbsp;preconceived notions, compelled to regard the plants as coniferous.

This genus is so much like the Nageia section of Podocarpus, that I have felt considerable hesitation in making it a distinct genus. It may be anbsp;question whether or not some of the species hitherto described as Podo-mmites in other formations besides the Potomac should be regarded as belonging to Nageiopsis. In the absence of branching twigs it is not alwaysnbsp;easy to distinguish these plants from Podozamites. In the leaves of thisnbsp;plant, however, the nerves do not converge and unite in the tips as in Podozamites. This is the only feature which will distinguish detached leavesnbsp;of the two genera.

I am strongly inclined to think that Podozamites Emmonsi, Newberry, from the Rhsetic of North Carolina and Virginia, as well as Podozamitesnbsp;tenuistriatus, from the same formation, belong to Nageiopsis.

Plate LXXV, Fig. 1; Plate LXXVI, Figs. 2-�; Plate LXXVII, Figs. 1, 2; Plate LXXVIll, Figs. 1-5;

Leafy twigs very large, with stout woody stems sometimes 1�� and over thick; leaves strap-shaped, narrowed at the base, attached by a short,nbsp;slightly twisted petiole most commonly to the margin of the stem, rarelynbsp;within it on the upper and lower face, acute or subacute, and graduallynbsp;narrowed towards the tips, varying in width and length ; maximum length

seen 18� and over, maximum width 1� and over, usually remotely placed, generally opposite, rarely subopposite, going off normally at an angle ofnbsp;about 45�, but often from pressure distorted in position; nerves comparatively few, forking at or near the base, parallel to near the apex, wherenbsp;they are slightly crowded.

Localities: Fredericksburg; Kankey�s; near Telegraph Station; 72d mile-post, near Brooke; Deep Bottom; red-clay ball in banks of Dutchnbsp;Gap Canal; fishing hut above Dutch Gap Canal.

This splendid plant is quite widely diffused, but it is rare at all points except Fredericksburg, where it is not uncommon ; all the larger specimensnbsp;figured come from this latter locality. PI. LXXV, Fig 1, slightly restored,nbsp;shows that the leafy twigs must have attained great dimensions, for this isnbsp;evidently but a'small portion of the twig. PI. LXXVIII, Figs. 1, 4, mustnbsp;form portions of still larger twigs. Fig. 3 of this plate shows a sort of keelnbsp;on the stem, probably due to shrinking. On this the leaves are not strictlynbsp;distichous PI. LXXVII, Fig. 1, shows leaves of the greatest width. Innbsp;Fig. 2 of the same plate the position of the leaves is due to distortion fromnbsp;pressure acting downwards. PI. LXXVI, Fig. 4, gives leaves of unusualnbsp;width On Fig. 5 of the same plate we see the scars left by the bud-scalesnbsp;of a terminal bud. PI. LXXVI, Fig. 3, shows at the top of the stem thenbsp;bases of two lateral branches. It seems that this plant often continued thenbsp;growth of its leafy branches by means of a terminal bud flanked by twonbsp;lateral buds. On Fig. 5 there are indications at the place marked by thenbsp;scars of the bud-scales that two lateral branches had been torn away.nbsp;Before I saw the specimen depicted in Fig. 3 I supposed that the plantnbsp;was a Podozamites close to Zamitcs Gcepperti Schenk.^ In the character ofnbsp;the leaves it is much like this plant; Schenk�s plant is evidently muchnbsp;mutilated.

Leafy twigs wide-spreading, copiously branching; leaflets varyin good deal in length and width according to position, those at the base ofnbsp;the branches sometimes unequal and much smaller than those up higher.

The leaflets attain a maximum width of 2�� and a length of 7��. They are widest near the base, and taper gradually to an acute tip, are abruptly narrowed at base and rounded off, attached by a very short, slightly twistednbsp;foot-stalk mostly to the sides of the stem, usually distichous, varying innbsp;shape from narrowly ovate to linear-lanceolate, opposite nearly always;nbsp;nerves remote and distinct, forking at or near the insertion of the leaves,nbsp;diverging strongly on entering the leaf, and almost parallel to near thenbsp;summit, where they are more crowded together, the outer ones terminatingnbsp;in the margins below.

Localities: Fredericksburg; banks of Dutch Gap Canal; fishing hut above Dutch Gap Canal.

This fine plant is abundant at Fredericksburg, but it is quite rare at other localities, only a few imperfect specimens being found, as, for example, at Dutch Gap. As will be seen from the figures, the leaves vary anbsp;good deal in size, shape, and distance apart; the smaller are often morenbsp;crowded than the larger ones. The fine specimen given in PI. LXXIX, Fig.nbsp;1, apparently branched several times. In PL LXXX, Fig. 1, a thick strongnbsp;stem is shown, and the leafy twig had evidently considerable length, thenbsp;leaves being comparatively remote from each other. Fig. 4 of the samenbsp;plate gives fragments of a copiously branching stem, the junction of onenbsp;terminal and two lateral twigs being shown radiating from a common point,nbsp;which seems to be a usual mode of branching in the plants of this genus.nbsp;Tlie two lower left-hand twigs seem to come off in a similar manner fromnbsp;down lower on the stem. The leaves on this specimen are much crowded.nbsp;In PL LXXXI, Fig. 1, we have apparently the same mode of branching.

This plant, in the nerves and shape of the leaflets, is so much like a Zamites, rhat for some time I held it to be a cycad. It is the most abundantnbsp;species of Nageiopsis found at Fredericksburg. Unlike the leaves ofnbsp;Zamites and Vodozamites, those of this and the other species of Nageiopsisnbsp;seem to be quite persistent, for they are usually found attached to the stem.

Stems stout, leaves remote, recurved, subacute to obtuse, gradually narrowed to the base, and attached to the margin of the stem, or slightly

�within it, by a comparatively broad flat pedicel, in shape elongate-elliptical to oblong, length reaching and width 15��. Nerves fine, numei�ous,nbsp;closely placed, forking near the base, and parallel to near the summit, wherenbsp;they are a little more crowded; the outer nerves on the upper margin endnbsp;in the margin of the leaves some distance below the summit.

Localities: Fredericksburg; banks of Dutch Gap Canal; fishing-hut above Dutch Gap Canal. It is most common at Fredericksburg, but is rarenbsp;everywhere.

Leaves with very thick stems even at the summits of the leafy twigs; leaflets attaining very considerable dimensions; length not made out, widthnbsp;up to 27�� and over, gradually narrowed to the base and tip; elongate-elliptical in shape, attached by a short slightly twisted pedicel to the marginnbsp;of the stem, or slightly within it; nerves at the base and summit of thenbsp;leaves, so far as seen, indistinct and not well made out, fine and rathernbsp;remote.

Localities: Road-side near Potomac Run; Fredericksburg; Kankey�s; 72d mile-post, near Brooke; banks of Dutch Gap Canal; fishing-hut abovenbsp;the canal.

The plant is rare, and having long narrow leaves, with a thin leaf-substance, the leaves are usually found detached and in fragments; in this respect it is more like Zamites than most of the species of Nageiopsis. The nerves are usually so fine and the leaf-substance so thick, that they can notnbsp;be clearly made out. It is not certain that some of the specimens placednbsp;in this species are not Zamites.

Leaves very broad and short, base and apex not seen; leaf-substance thin; shape of leaves probably broadly elliptical; nerves not fully disclosed,nbsp;but probably branching near the base; they are then approximately parallelnbsp;to near the apex, following the margins, and parallel.

Localities: Fishing-hut above Dutch Gap Canal; road-side near Potomac Run; very rare.

Several detached leaves of this plant were found at the fishing-hut above Dutch Gap Canal. They occurred together, as if coming from thenbsp;same plant, but were detached so as to give no intimation of the mode ofnbsp;attachment, kind of stem, etc. The most complete of these leaves is givennbsp;in the figure. Fragments indicating even greater width than that of the onenbsp;figured were seen. The maximum dimensions indicated were 12�� by 5��.nbsp;It is possible that this plant is a broad-leaved Podozamites, similar to thenbsp;broad-leaved forms such as Podozamites Beinii Geyler, described by Geylernbsp;from the Jurassic formation of Japan. (Ueber Foss. Pflanzen aus dernbsp;Juraform. Japans, PI. XXXIV, Fig. 2.)

Leaves, so far as seen, small, closely placed, narrowed at the base and apex, diminished greatly and abruptly in ascending on the leafy twigs, innbsp;shape narrowly oblong to linear; nerves forking at base, parallel to nearnbsp;the apex, the outer ones ending in the margins just below the apex.

Only one specimen of this plant was found. It shows the peculiarity of a sudden diminution of the leaves in ascending. As a rule the leavesnbsp;of the species of this genus diminish towards the lower portions of thenbsp;leafy branches if there is any inequality in them.

Stems comparatively very stout; leaves opposite, going off nearly at right angles from the stem, closely placed, lower ones smaller but graduallynbsp;increasing in ascending, broadest near the base and abruptly rounded offnbsp;there, attached by an extremely short slightly twisted pedicel, narrowingnbsp;to an acute tip, oblong to elongate-elliptical in shape; nerves indistinct,nbsp;but forking at base, diverging on entering the base of the leaf, then nearly

parallel to the tip, where they are somewhat crowded, the outer ones ending in the margin below the apex.

The specimens of this pretty plant are quite rare. The lower leaflets are markedly smaller than those higher on the leafy twigs, but this is anbsp;feature not uncommon in plants of this genus.

Leaves short in proportion to width, very obtuse, attached by a short slightly twisted pedicel, broadly elliptical or oblong in shape, broadestnbsp;near the base, slightly inequilateral at base; nerves forking once or twicenbsp;near the base and then parallel to near the summit, where they are a littlenbsp;crowded together, the outer ones ending in the margins a little below thenbsp;apex.

This plant was evidently very rare. It shows the unusual feature of having the margin of the base on the lower side more convex and broadernbsp;than on the upper side, which latter is cut away in a concave manner.nbsp;The nerves also tend to go off in bundles, branching more than once atnbsp;the base of the leaves. It is very rare.

Leaves snort and broad in proportion to length, slightly inequilateral at base, obtuse, elliptical, broadest near base, abruptly narrowed on thenbsp;lower side at base, and more gradually rounded off on the upper side;nbsp;leaf-substance very thick, epidermis dense and shining; nerves not distinctly seen, but parallel towards the upper part, and slightly crowded atnbsp;the summit of the leaflets.

Only one specimen of this plant was found. The thick epidermis obscures the nerves.

Leaves narrowly ovate, widest at base and slightly acuminate, abruptly rounded off at base and attached by a short strong pedicel, gradually narrowed towards tips; nerves not seen.

Only one good specimen seen. It shows a small bit of the stem still attached. As no large amount of material was obtained at this place thenbsp;rarity of the plant may be apparent rather than real. It is possible thatnbsp;the plant may be a Zamites.

Stems large, branching freely; leaves small, narrowly ovate to oblong-linear, widest near the base and usually rather abruptly rounded off there, attached by a very short slightly twisted pedicel; gradually narrowed tonbsp;acute tips; leaves sometimes varying irregularly in size, larger and smallernbsp;ones being intermingled or placed on opposite sides of the stem; leafynbsp;branches terminating in a leaf similar to the lower ones; nerves forkingnbsp;once or twice near the base of the leaves, then parallel to near the summit, where they are more approximate, the outer ones ending in the margins below the summit.

This pretty little plant is not uncommon at Fredericksburg. It shows the peculiar feature (as in PI. LXXXVI, Fig. 7, and PI. LXXXVIII,nbsp;Fig. 2) of having the leaves at the bases of the twigs very unequal onnbsp;opposite sides, and also, as in the first-named figure, the peculiarity of having small leaves intermingled with large ones. In PI. LXXXIV, Fig. 4,nbsp;tlie tips of the leaves have been removed by accidents of preservation.

Leafy twigs pinnately arranged, terminating in a leaf larger than those lower down; leaves very small, narrowed to the base and apex, ellip-

tical or oblong, acute to acuminate, attached by a very short pedicel; nerves forking near the base, then parallel to near the tips, where they arenbsp;more crowded.

Localities: Fredericksburg; road-side near Potomac Run; fishing hut above Dutch Gap Canal.

The plant is not uncommon at the Dutch Gap locality, but is comparatively rare elsewhere. The best specimens (as PI. LXXXVI, Fig. 5) come from Fredericksburg. Fig. 3 of the same plate, having its leavesnbsp;widest at base and abruptly rounded off there, comes from the Potomacnbsp;Run locality, and is possibly a different species. PI. LXXXV, Fig. 14,nbsp;shows a stem of unusual thickness.

Plate LXXXVI, Figs. 8, 9; Plate LXXXVII, Figs. 2-6; Plate LXXXVIII, Figs. 1, 3, 4, 6-8; Plate

Leafy stems large, branching copiously and wide-spreading; branches often opposite, swollen at their attachments to the main stem, and markednbsp;with scars left by the bud-scales; the leafy stems often subdivided towardsnbsp;their ends into smaller branches on which the leaves are much diminished;nbsp;leaves varying much in size, very long in proportion to width, naiTOwlynbsp;linear-acute to acuminate, generally very remotely placed, narrowed gradually to apex and base, attached by a short twisted pedicel generally to thenbsp;sides, sometimes to the upper and lower surfaces of the stems slightlynbsp;within the mai�gin ; nerves forking near the base and then parallel to thenbsp;summit, the outer ones terminating in the margin below the summit ofnbsp;the leaves, quite strong.

Localities: Fishing hut above Dutch Gap Canal; road-side near Potomac Run; 72d mile-post; bank near Brooke; Fredericksburg; near Telegraph Station; Fort Washington.

This fine species is one of the most widely diffused of the Potomac plants, and is the most generally distributed species of Nageiopsis. It isnbsp;not very rare at the Dutch Gap locality, but is most common at Fredericksburg, where the plants given in PI. LXXXVI, Figs. 8, 9, and PI.nbsp;LXXXVII, Fig. 2, occur. It is one of the most noteworthy connecting

links between the plants of the various localities which, as has been stated, show so much tendency to isolation and local distribution. It is foundnbsp;with the numerous Angiosperms of the two localities near Brooke, and connects these with the plants of Dutch Gap and of Fredericksburg. Somenbsp;of the leafy stems must have been very large and wide-spreading.

On some of the branches at their bases there are very distinct scars left by the scales which invested the terminal buds. The branches seem commonly to have formed at their extremities a terminal and two opposite lateral buds with which to continue the growth in the next season. The formation of such buds on these plants and on Cephalotaxopsis indicates thatnbsp;there were well-defined pauses in the growth of the branches. The leavesnbsp;seem to have been very persistent, as they are usually attached to thenbsp;stems.

The specimen given in PI. LXXXVI, Fig. 9, indicates well the copiousness of the branching of this plant. It shows on the left hand atnbsp;base what seems to be a portion split off from a large stem, and attachednbsp;to this is a lateral twig, which has at base the marks of bud-scales. Nearnbsp;its summit this in turn sends off two opposite lateral twigs. This specimennbsp;and also that of PI. LXXXVIII, Fig. 8, show that the leaves tend to diminish in size when the twigs split up into subordinate branches. This plantnbsp;in its mode of branching and in the shape of its leaves, as well as in tlienbsp;arrangement of the scars of the bud-scales, is much like Oephalotaxopsis, butnbsp;it has several nerves in the leaves.

Stems comparatively very stout; leaves narrowed gradually to the base and apex, subacute, subfalcate, attached by a short slightly twistednbsp;foot-stalk; leaf-substance thick and leathery; nerves not seen, but apparently several, and as in Nageiopsis.

Only one specimen of this plant was found. Its position is doubtful, and it may be a Sequoia, for the foot-stalks seem to be decurrent. Theynbsp;leave imprints on the stem resembling those of Sequoia.

Leafy stems branching copiously and irregularly; leaves small, opposite, very thick, of varying sizes on the same branch, varying a good deal in shape, broadly ovate, broadly elliptical or orbicular, broadest at base,nbsp;abruptly narrowed into a short slightly twisted pedicel, obtuse to subacute, terminal leaflet of the twigs like those lower down; nerves usually notnbsp;distinct, being immersed in the thick leaf-substance, radiating palmateh^nbsp;from a common point at base, and forking once or twice.

This genus is quite rare in the Potomac flora, and as yet shows only one species. Its character and place can not be fixed positively from, thenbsp;small amount of material found. It is strikingly like Phyllocladus in manynbsp;respects. In some features it resembles Nageioj)sis, but the nerves have anbsp;different chai�acter. The genus is provisionally formed and named fromnbsp;the resemblance to Phyllocladus.

Plant with the generic character, having the terminal leaflet of the twigs much larger than those next below, and in shape ovate-obtuse; leafynbsp;branches keeled.

Leaves linear-oblong, subspatulate, tapering gradually below to a broad petiole-like base, mode of attachment not seen ; leaf-substance thicknbsp;and glossy, at summit rounded and very obtuse; nerves distinct and prominent, single and parallel for a short distance above the lowest visiblenbsp;portion of base, then forking all nearly at the same height, with branchesnbsp;parallel to near the summit; at summit curving round to meet one another,nbsp;with a strong nerve uniting the abutting nerves. This peculiar plant isnbsp;much like Ileer�s genus Feildenia, from the Miocene of Greenland.

Plant with the generic character, having very strong broad nerves, which are sharply defined like threads in the dense leaves, the latter havingnbsp;a glossy look, and seeming to narrow so as to form a sheathing or claspingnbsp;base. The nerves of this species are quite like those of Heer�s species Feil-denia Mossiana,^ curving around to abut at the summits of the leaves, and thenbsp;points of meeting are connected by a strong nerve, which descends andnbsp;seems to split up to form the central pair of nerves.

Leaves borne towards the ends of the branches I; leafy branches pin-nately arranged, opposite or subopposite, in the same plane with the leaves, diminishing in ascending in the size and number of the leaves; towards thenbsp;summit of the leafy stem the leafy branches reduced to simple leaves; thenbsp;leafy stem terminated by a simple leaf similar to those of the brandies andnbsp;stem lower down; leaves on the lower branches pinnately arranged, subopposite or alternate ; lower leafy branches terminating, as does the main stem,nbsp;by a single leaf; leaves attached pinnately to the branches by short pedicels, in shape like a fan, with wedge-shaped bases, divided nearly to the basenbsp;into several principal segments or lacinise, usually two or three in number,nbsp;these in turn divided into a varying number of subordinate segments, andnbsp;the latter divided into a number of ultimate lacinise, which are strap-shaped,nbsp;of varying width and length, and end in teeth; the lacinise of various ordersnbsp;subdivided dichotomously, diverging slightly ; the nerves branch repeatedlynbsp;in a dichotomous manner, beginning in the pedicel, the branching taking-place at varying heights; the nerves diverge in a flabellate manner, andnbsp;one or two of the ultimate branches end in the teeth terminating the ultimate lacinise; they are slender but distinct; fructification not positivelynbsp;made out, but apparently in the form of very small rounded or elliptical

' Flor. Foss. Ai�ctica, vol. 5, Ft. 1, Die Mioc. Flor. des Grinnell-Landes, PI. Ill, Figs. 2-5.

nut-like seed, that are borne on short pedicels on each side of slender stems, which spring from the main stem like the leaves, and appear to representnbsp;metamorphosed leaves.

This curious group of plants has its single leaves in shape and nervation strikingly like those of Jeanpaulia, and in some cases they are much like those of Baiera. Before the more complete specimens werenbsp;found, showing the mode of attachment of the leaves, I thought that thenbsp;plants belonged to the genus Baiera. Heer united the plants formerlynbsp;called Jeanpaulia with Baiera; but there would seem to be a very considerable difference between such a plant as Jeanpaulia Mimsteriana, given bynbsp;Schenk,^ and Heer�s Baiera longifolia. The leaves of Schenk�s plant appearnbsp;to be compound, composed of pinnately arranged segments with a terminalnbsp;segment. The plan of this leaf is much like that of the leafy branches ofnbsp;Baieropsis, and it may be a question whether or not this Rhsetic supposednbsp;leaf is really a leafy branch. There is also some resemblance between thenbsp;mode of segmentation of Baieropsis and that of the plants which Heer^nbsp;called Jeanpaulia borealis, and J. lepida, and which in the fourth volume ofnbsp;the same work he was inclined to think might be ferns. But these twonbsp;plants have much shorter and proportionally broader lobes than those ofnbsp;Baieropsis. Baieropsis in some points is like Saporta�s genus Ginkgophyllum.nbsp;In this latter, however, the leaves are flabellately divided only towards theirnbsp;summits and very sparingly segmented, while the greater portion of theirnbsp;length in their lower portions is strap-shaped, and these long strap shapednbsp;basal portions unite at their insertions to form a wing along the midrib.nbsp;Some of the leaves of Baieropsis are in shape much like those of somenbsp;forms of Adiantum. These might be regarded as Oinhgos, were it not fornbsp;the pinnate ar-rangement of the leaves.

These forms, which I have united under tne generic name Baieropsis, seem to have more of the characters of the Grinkgo section of broad-leavednbsp;conifers. They are most probably nearly allied to GinkgopJiyllum andnbsp;Baiera, but still in some of the forms fern characters ai-e to some extentnbsp;present, and so long as the fructification is not clearly made out, the truenbsp;place of the group can not be positively determined.

The nature of the apparent fructification is obscure from the poor preservation of the specimens, and from the fact that the precise connectionnbsp;of the seed-like bodies with the leaves is not seen. The seeds are aboutnbsp;2quot;�� in diameter, are sessile or attached by very short pedicels to slendernbsp;naked stems, being opposite or subopposite, and on both sides of them.nbsp;The stems with their seeds seem to represent metamorphosed leafynbsp;branches or leaves, taking the place of the ordinary leaves, which appearnbsp;higher. The general character of these seeds and their apparent mode ofnbsp;attachment remind one of the supposed seed of Baiera Miinsteriana fromnbsp;the Rhsetic of Baireuth, which represent metamorphosed leaves of that

Plate LXXXIX, Figs. 1, 3; Plate XC, Fig 1. ; Plate XCI, Fig. 2; Plate XCII, Pig. 5.

Leaves very large, having probably the width of 12��, and the length of over 15��, attached by slender pedicels, and apparently distributed asnbsp;given in the generic description�i. e., pinnately on leafy twigs, whichnbsp;themselves are arranged pinnately on a principal stem, the main stem andnbsp;branches ending in leaves of the normal kind; leaves divided to nearnbsp;their bases into several principal lacinim, which in turn are subdivided atnbsp;varying heights into subordinate laminse, and these into ultimate ones thatnbsp;are long and narrow, ribbon-like, with the ends not seen; all subdividenbsp;dichotomously and diverge so as to give the leaf a fan shape; the ultimatenbsp;lacinim l.5�� wide and under; the nerves distinct, although slender. Theynbsp;fork at the base in tlie primary lacinise, and then repeatedly subdivide dichotomously in the lacinim at varying intervals, the branches being more ornbsp;less parallel.

Localities: Fredericksburg; red clay ball in the banks of Dutch Glap Canal; fishing hut above the canal; entrance to Trent�s Reach.

In some specimens the apparent simple strong nerves under a good lens seem to run in pairs, the members of which are so closely placed thatnbsp;they seem to the unaided eye to be simple nerves. This fine plant is notnbsp;very rare at Fredericksburg in pretty good specimens. At the other localities the great size of the leaves caused them to be preserved in a verynbsp;fragmentary state.

There is a strong resemblance between the fragments, of some of these leaves and Baiera cretosa^ Schenk, but Schenk�s figure indicates a largernbsp;and coarser leaf.

Plate LXXXIX, Fig. 4 ; Plate XC, Figs. 2-5 ; Plate XCT, Pigs. 1, 3, 4, 7 ; Plate XCIP Figs. 1, 2, 6.

Leafy branches with the character of the genus; stems slender, leaves broadly fan-shaped, opposite or subopposite, attached by short pedicels,nbsp;usually divided down to near the base into three principal segments; thesenbsp;by repeated dichotomous subdivision give rise finally to long, slender, ultimate segments, that are strap-shaped and about wide, their length notnbsp;being made out, as their tips were not in any case seen, but in the largestnbsp;leaves probably .attaining the length of 4�� and more from the last point ofnbsp;subdivision; the nerves slender but distinct, forking at the base to enter thenbsp;principal lacinim, and then forking repeatedly and dichotomously at longnbsp;intervals, with the branches nearly parallel, one or two being found in thenbsp;ultimate lacinise. The apparent fructification (see PI. XC, Fig. 4) is as givennbsp;in the generic description.

Localities; Entrance of Trent�s Reach; banks of Dutch Gap Canal; red clay ball; fishing hut above the canal.

The plant is not uncommon at the first and last named localities. It is usually associated in its occurrence with Bioonites Buchianus. There is anbsp;considerable variation in the size of the leaves and in the number of theirnbsp;segments, apparently depending on the position of the leaves on the leafynbsp;twigs, those towards the sitmmits being smaller and with fewer segments.nbsp;The largest and most perfectly preserved forms were found at the entrancenbsp;to Trent�s Reach. The leaves were usually found in a very fragmentarynbsp;state, and in no case were their tips seen.

Twigs and leaves as in B. pluripartita, but much smaller and constantly so, without gradations into the larger form; the ultimate lacinise very nu-

inerous and narrow, being under l��in width; the leaves attain a maximum length of 4��, but mostly are under that, and have a maximum width ofnbsp;3.5��, but generally are narrower; nerves as in B. pluripartita, but morenbsp;subdivided, closer, and more delicate.

The specimens of this plant are much more numerous than those of B. pluripartita, but they are mostly very fragmentary. This is the most common Baieropsis at Dutch Gap, and it is the most common plant in the rednbsp;clay ball which occurs in the banks of the canal. It appears in numerousnbsp;fragments poorly preserved at the entrance to Trent�s Reach, being foundnbsp;in the same layer with Frenelopsis parceramosa, and Dioonites Buchianus.nbsp;The lower right-hand leaf in PI. XCII, Fig. 3, is nearly a complete one,nbsp;wanting only the tips of the ultimate lacinise, which no doubt, as in B. pluripartita, terminated in teeth. The above-mentioned leaf is one of the largestnbsp;found in this plant.

Leafy branches abruptly changed to leaves in ascending (Fig. 4); lower leafy branches of the main stems having on the upper side simple leaves, butnbsp;on the lower side, towards the base, possessing leafy branches of the normalnbsp;type in place of the simple leaves of the upper side; leaves and leafynbsp;branches closely placed; leaves quite small, fan-shaped, short, mostly divided nearly to the base into two principal laminae, both of which are subdivided a little above the base into laciniae; these in turn, by dichotomousnbsp;subdivision, give short strap-shaped lobes, which end in two shallow acutenbsp;or narrowly elliptical teeth, or else in two narrowly oblong subacute teeth;nbsp;nerves forking at base and then repeatedly forking in a dichotomous manner, so that the branches from the last forking end in the teeth.

At the last-named place the plant is very rare, but it is abundant at the bank near the railroad in the vicinity of Brooke. Here it is, with the exception of the angiosperm leaves, the most common fossil. There is somenbsp;variation in the size of the leaves and in the number of subdivisions, somenbsp;MON XV--14

of the leaves, as in Figs. 5, 6, being larger than others, as in Fi, Strange to say, these leaves, although so abundant at the bank near Brooke,nbsp;show not a single specimen at the 72d mile-post, only a few hundred feetnbsp;distant.

Stems of the leafy branches proportionally stout; leafy branches and leaves alternate; leaves fan-shaped and wide in proportion to length,nbsp;divided to near the base into two principal laminae, and those a little highernbsp;subdivided into two subordinate laciniae which repeatedly subdivide untilnbsp;the ultimate laciniae end in two linear subacute teeth of comparativelynbsp;great length; nerves repeatedly forking flabellately, so that the ultimatenbsp;branches end in -the teeth.

Leaves subopposite, narrowly fan-shaped to wedge-shaped, quite narrow in proportion to their width; leaves attached more obliquely than in B. denticulata, but with the lacinim and nerves as in that species, thenbsp;lacinife being fewer in number.

Leaves very long in proportion to their width, deeply cut into very long and slender principal lacinim, which are two in number and divergenbsp;slightly; these are subdivided several times into long and slender laciniae,nbsp;finally giving long narrowly strap-shaped ultimate laciniae which arenbsp;and under in width, the tips not seen; arrangement of the leaves as givennbsp;in the generic character; nerves rather indistinct, but as in B. pluripartita ;nbsp;the main stem quite slender.

This plant has a decided facies of its own, due to the slenderness and the length of the lacinise. The subdivisions of the leaves are much fewernbsp;than in B. expansa and B. pluripartita, and take the form of pairs. It isnbsp;quite rare.

Stems moderately strong; leaves subopposite to opposite, closely placed, often imbricated, subquadrilateral to flabellate fan-shaped, narrowed to a wedge-shaped base, and attached by a short pedicel whichnbsp;springs from the lower corner of the leaf, so that the inner margin of thenbsp;leaves runs close to the main stem, parallel with it, and often overlappingnbsp;it, while the lower margin of the leaves stands nearly at right angles withnbsp;the main stem ; leaves cut down to near the base into two principal lacinise,nbsp;and those higher cut into two or more minor lacinise ; ultimate laciniae verynbsp;shallow and strap-shaped, ending in acute very short teeth, or rarely innbsp;narrowly elliptical and subacute ones; all the laciniae turned outwards ornbsp;upwards, the lower margins of the leaves being entire or having sometimesnbsp;an acute tooth; leaves in ascending towards the tips of the leafy branchesnbsp;have their lower margins directed more and more upwards, become smaller,nbsp;assume more of an elliptical or a wedge shape, have the laciniae only onnbsp;the upper margin, and finally coalesce to form a terminal leaflet, which atnbsp;base shows three segments, but whose terminal portions are not seen;nbsp;nerves fine but distinct, branching at base from a mother nerve and thennbsp;dividing repeatedly in a dichotomous manner so as to fill the laminae, andnbsp;have the branches ending in the teeth.

Localities : Fredericksburg ; road-side near Potomac Run ; near Telegraph Station.

The plant is most frequent at Fredericksburg but is not abundant there, and is usually in a very fragmentary state. If we look to the shapenbsp;of the leaves alone this curious plant is much like a fern of the type ofnbsp;Adiantum, but the gradations through different forms connect the specimens so closely with the flabellate leaves of Baieropsis that they can not

be separated bj any good distinctions. The principal difference from the more common and typical forms of Baieropsis is found in the greater proportional width of tlie leaves and the smaller depth of the subdivision.

Leaves nearly in shape as those of B. adiantifolia, but much smaller, alternate, with their lower margins making an angle of 45�, with the stemsnbsp;divided above the base into two lacinise, one smaller, directed upwards,nbsp;and divided near the summit into short strap-shaped lacinise that end innbsp;teeth, and one larger, directed outwards, also subdivided into strap-shapednbsp;lacinifE; nerves as in B. adiantifolia.

This may be only the upper part of a small branch of B. adiantifolia. It is very rare.

Leaves very large, dividing repeatedly into lacinim and diverging flabellately; form and dimensions of the leaves not made out; ultimatenbsp;lacinim, so far as seen, wide; nerves forking at long intervals, with thenbsp;branches parallel.

Only a few specimens were found. The leaf was probably very large, the fragments indicating a maximum length of about 20��, with anbsp;nearly equal width. The great size of the leaves caused them to be preserved only in fragments. It is possibly a Baiera. The plant has on thenbsp;wider basal portions of the lacinise a number of peculiar elliptical protuberances, which seem to spring from off-shoots of the nerves. The exactnbsp;nature of these could not be made out, but they seem to be rather anbsp;fungoid growth than fructification.

Leaves leathery, gradually narrowed into the longer or shorter pedicel, fan-shaped, with repeated dichotomous subdivision, segments linear, some-

times ribbon-shaped, incised at the tips or entire, inserted on short branches; nerve-bundle issuing from the base of the leaf and repeatedly forking.

This description, which is that given by Schimper on page 261 of the second volume of Zittel�s Handbook, applies to only one of the forms ofnbsp;the Potomac. The essential point is the insertion of the leaves in tufts onnbsp;the summit of short branches which form annually. This is a verynbsp;different arrangement of the leaves from that in Baieropsis, where they arenbsp;all in one plane, arranged pinnately on the sides and at the tips of leafynbsp;twigs.

Leaves numei�ous, grouped in bundles or tufts at the summit of short, stout, annual growths, having their basal portions long, slender, and gradually narrowing into a pedicel; their upper portions dichotomously dividednbsp;into a small number of strap-shaped lacinise, the ultimate ones being a littlenbsp;over wide; nerves slender, forking at long intervals, with branchesnbsp;parallel.

This plant, evidently a true Baiera, is very rare, the specimens, few in number, being, with the exception of the one figured, found in small fragments. The leaves at the summit of the short twigs seem to have beennbsp;very numerous and more slender than in the Jurassic Baieras.

Trees or shrubs; stems seen in thickness up to 5�� and more; stems and branches cylindrical, jointed, branches alternate or whorled, radiatingnbsp;from the same zone on the principal stems and curving upwards; epidermis dense and durable, cortical tissue thick, and apparently succulent;nbsp;leaves on the joints very short, varying somewhat in shape, normally morenbsp;or less triangular in form, acute, close appressed, not decurrent, minute andnbsp;scale-like, one to three in number, alternating in position on the successivenbsp;joints; epidermis marked with minute tubercles arranged in rows, whichnbsp;to the unaided eye appear as fine strias running longitudinally on the stem

and parallel to one another; woody axis of the larger branches and stems comparatively small, in the ultimate smaller branches apparently wanting,nbsp;these being composed seemingly of a succulent material, which was covered by a dense, durable epidermis; fruit not seen.

The stems and branches of this plant, originally cylindrical, are now from pressure always found flat. The stems and larger branches are generally found decorticated or deprived of their epidermis. The removal ofnbsp;the epidermis carries away the scale-like leaves, and on the smallest ultimate twigs they in such cases leave no scars But when the stems andnbsp;largest branches are deprived of their epidermis and not decorticated,nbsp;rhombic or triangular scars mark the place of the leaves on the joints.nbsp;The larger twigs quite often are arranged on the main stems in an umbellate manner. In^ other cases the branches are arranged in the same planenbsp;and go off alternately

The genus Frenelopsis, as hitherto known, is composed of only two species, viz, F. Hoheneggeri Schenk, and F. occidentalis Heer. The formernbsp;is, according to Schenk, the most abundant plant in those beds in which itnbsp;occurs. He gives in Die Foss. Pflanzen der Wernsdorf Schichten, the mostnbsp;complete description and delineation of this species known. We may then,nbsp;in our comparative study of this Potomac species, confine ourselves tonbsp;Schenk�s figures and description. Schenk, in his description of the leaves,nbsp;says (page 13) that they occur in pairs opposite to each other, the succeeding pairs being decussate. The leaves of one of the Potomac species certainly occur in whorls of three, and, judging from the figures given bynbsp;Schenk, I am inclined to think that the leaves on F. Hoheneggeri occur also innbsp;threes on the joints. In PI. VI, Fig. 6, in Schenk�s work, the pair of leaves innbsp;the middle of the stem seem to present on the front aspect of the twig thenbsp;greater portion of their width, and by their position strongly suggest thatnbsp;they are opposed behind by a single leaf, which belongs to the same whorl.nbsp;The lower leaf on this twig, by its eccentric position, indicates that it isnbsp;opposed behind by two leaves. The position of the pair above mentionednbsp;is quite similar to that seen in some specimens of the Potomac plant F.nbsp;ramosissima, where the pair is opposed by a single leaf. If this be thenbsp;true character of the arrangement of the leaves, then Schenk�s opinion, ex-

pressed on page 15 of the above-named work, is correct, and the plant is nearly allied to Frenela It is perhaps the ancestral form of the livingnbsp;Fremela, not yet fully differentiated, for the Potomac plant F. parceramosanbsp;has only one leaf on each joint.

Heer�s F. occidentalis from Valle de Lobos, Portugal, does not afford specimens well enough preserved to add to our knowledge of the genus.nbsp;In his Contributions a la Flor. Foss, du Portugal, PL XII, Fig. 4, is a goodnbsp;deal like some of the specimens of F. ramosissima.

The striking resemblance of the Potomac forms, and especially of F. ramosissima, to Frenela confirms Schenk�s original conclusions, and therenbsp;seems to be little doubt that Frenelopsis is more nearly allied to that genusnbsp;than to Ephedra, as Heer thought. If the leaves of F. Hoheneggeri arenbsp;really in pairs, then the generic description must read; Leaves one to threenbsp;on the joints. This would not be incompatible with a relationship to Frenela, for in that genus the leaves are not always in threes, but occur occasionally in fours, or even scattered singly, as sometimes is the case in Frenela australis Hooker. Leaves in fours occur also in F. suhumbellata Par-latore.

Schenk^ very correctly calls attention to the resemblance between F. Hoheneggeri and Massalongo�s Aularthrophyton, depicted in Flor. Foss, delnbsp;Monte Colle, etc. There is so strong a resemblance that it is difficult tonbsp;believe that they belong to different genera.

F. ramosissima is probably a better differentiated form in the direction of Frenela than F. parceramosa and F. Hoheneggeri.

Tree or large shrub; stems seen up to a diameter of 5��; stems and branches originally cylindrical, now from pressure always flat, apparentlynbsp;with a large pith, often appearing to have been hollow; the larger branchesnbsp;sometimes scattered and alternate, but more commonly in umbel-likenbsp;whorls containing three to five branches, usually in the larger branchesnbsp;curving upwards; stems and branches jointed, with joints usually very

short, the jointing most conspicuous on those parts which retain the cortical layer and epidermis, especially distinct in the smallest ultimate branches,nbsp;the jointing on the larger decorticated stems often not visible; woody axisnbsp;proportionally very small, apparently surrounded originally by a thick succulent cortical layer, which was covered by a firm, parchment-like, verynbsp;durable epidermis; this latter marked by very fine longitudinal linesnbsp;formed of rows of small tubercles or dot-like elevations; in the smallest ornbsp;ultimate branches the woody matter seems to have been almost or whollynbsp;wanting, the material composing the branch being succulent and coverednbsp;with a firm epidermis; leaves in whorls of threes, leaves of successivenbsp;whorls alternating; on the youngest branches the leaves are often retainednbsp;uninjured in the form of minute, closely appressed scales, mostly broadlynbsp;triangular in form, acute, often acuminate, sometimes mucronate, united atnbsp;base ; on the older branches often convex in form, and under a lens showing towards their tips a prominent line forming a sort of keel; on thesenbsp;branches, when deprived of epidermis, the leaves leave scars, rhornboidalnbsp;in shape, and slightly elongated in the direction of the length of the stems.nbsp;The shape of the older leaves varies more than that of the younger ones,nbsp;being broadly triangular, with very short acute tips or mucronate, sometimes dome-shaped to broadly conical, with tips prolonged to variousnbsp;lengths, often acuminate and sometimes mucronate; the ultimate succulentnbsp;branches, seeming to have performed the work of leaves and always short,nbsp;go off from the joints in the axes of the scale-like leaves, generally curvenbsp;upwards, and apparently lie in the same plane. The subordinate twigsnbsp;always end with a branch like those sent off lower down; ultimatenbsp;branches in length, stoutness, number of branches on the penultimate twigs,nbsp;and degree of crowding show considerable variation; in some cases thenbsp;ultimate branches are very closely placed, three or four on a side, with anbsp;terminal one short and stout, in other cases they are remotely placed, stoutnbsp;and long; again, the plants have sometimes on the penultimate twigs anbsp;few remote, very short branches, hardly more than buds; buds sometimesnbsp;found on short twigs, arranged as are the branches, forming club-shapednbsp;growths, in which a number of internodes with partially formed leaves arenbsp;shown.

The plant is very rare at Baltimore, but abounds at Fredericksburg, where it is by far the most common fossil. The great number of specimensnbsp;of this plant at the latter locality indicates that a forest of it must havenbsp;grown near by. The existence of well-defined buds shows that the gi�owthnbsp;of the plant was not continuous, but that periods of repose occurred. Innbsp;many cases the epidermis of the ultimate twigs is so well preserved that itnbsp;shows the entire shape and dimensions of the twigs, and may be strippednbsp;off from the stone. In such cases there is no trace shown of woody fiber^nbsp;and only a faint imprint is left. The entire material of the smaller twigsnbsp;was evidently pulpy and succulent. Only in the older and larger stems isnbsp;a small woody axis shown. In all cases the removal of the epidermis carried away the leaves, and these leave no scars except on the oldernbsp;twigs. It is quite common to find the shrunken remains of the twigsnbsp;lying in molds which are now considerably larger than themselves, andnbsp;which they evidently once filled. In twigs 1�� and under in diameter wenbsp;may often find the parchment like epidermis perfectly preserved, wrinklednbsp;transversely, filled with a brown dust, but showing no woody matter. Whennbsp;woody matter existed it has always been changed to jet, involving the totalnbsp;destruction of the tissue, so that its structure can not be made out. Thenbsp;woody axis, when present in the form of jet, is always much smaller thannbsp;the tube of epidermis which incloses it. It is a peculiar fact that the woodynbsp;matter of this plant was never found preserving the structure of the tissues.nbsp;This results, perhaps, from the succulent nature of the material. Tliis destruction of tissue and softening of the material of the plant may accountnbsp;for some peculiar differences seen in parts which evidently once belongednbsp;to the same plant. On some of the older stems, if some of the succulentnbsp;cortical zone remains, or if the epidermis is preserved, the jointing is plainlynbsp;shown. (See PI. XCIX, Figs. 2, 3; PI. XCVI, Fig. 3, etc.)

In other cases, where only the woody axis is preserved or nothing but an imprint is left, no indications of jointing can be seen, although on ultimate twigs of the same specimen which retain the epidermis the jointingnbsp;is plain. In the decorticated specimens figured on PI. XCVII, Figs. 1, 2;nbsp;PI. XCVIII, Fig. 2; Plate XCVI, there is no trace of jointing, the softening

of the tissues and the pressure to which it has been svrbjected, obliterating the evidences of it. In PI. XCVI, Fig. 1, the main stem shows no jointing,nbsp;while the ultimate and not fully decorticated twigs do show jointing; PI.nbsp;XCV, Figs. 1, 2, 3, 5, retaining epidermis, show good jointing.

The specimens with buds, as in PI. XCIX, Fig. 1, had thick fleshy stems, with a comparatively small woody axis, surrounded by a very thicknbsp;succulent cortical layer., It looks as if this material was provided to sustainnbsp;the growth of the buds. PL C, Fig. 1, gives a restoration of what was thenbsp;probable appearance of one of the smaller twigs. The smaller branchesnbsp;seem always to have been spread out in one plane and to have gone offnbsp;alternately. The tubercles seem to have been borne on the surface of thenbsp;epidermis. They are never conspicuous on this species, and are seen bestnbsp;on the youngest ultimate twigs, requiring the help of a lens to make themnbsp;out distinctly.

The most conspicuous features of this species are the copiousness with which the branching takes place and the shoiTness and smallness of thenbsp;branches. The ultimate branches of F. Hoheneggeri form usually very longnbsp;cylinders, which feature is never seen in this species.

Considering the great number of specimens found at Fredericksburg, it is most surprising that no trace of it has been found at any other Virginia locality. This gives us a striking instance of the localization of thenbsp;Potomac plants. This fossil foi�ms a type of Frenelopsis very near to Frenela,nbsp;and different in many respects from the other known species.

Tree or shrub; stems and branches originally cylindrical, now found flat from pressure; primaiy and subordinate branches very succulent,nbsp;jointed, wdth very short nodes, usually found in a very fragmentary condition ; epidermis parchment-like and very durable, having rows of minutenbsp;tubercles, which form distinctly visible longitudinal lines on the stem;nbsp;ultimate branches very long with, in tlie visible portions, but little diminution in the width, from pressure appearing as very narrow, strap-shapednbsp;twigs, arranged either in an umbellate manner or alternately in one plane,

remote or closely placed, varying much in width, viz, from 1�� to 12��; the maximum length of the largest ultimate branches seen, 13��; verynbsp;prone to break into fragments at the joints and very deciduous; leavesnbsp;very short and closely appressed, very broadly triangular generally, andnbsp;but little prolonged above the joint, often seemingly entirely undeveloped,nbsp;one on each joint, those of the adjacent joints alternating in position;nbsp;branches originally succulent and containing but little woody matter; innbsp;the ultimate twigs no woody matter is visible, and they appear to havenbsp;been composed of a durable epidermis surrounding a fleshy internal portion;nbsp;the ultimate twigs unbranched, and seeming to have been very long andnbsp;comparatively thick.

Locality: Found only at the entrance of Trent�s Reach, and there almost wholly in a layer 6 to 9 inches thick near the top of the Potomacnbsp;beds.

This remarkable plant is more like Frenelopsis HoJieneggeri Schenk, than is F. ramosissima. It has larger epidermal tubercles than this latternbsp;fossil, and they make lines in the direction of the length of the stems thatnbsp;are plainly visible to the unassisted eye. This plant has the same long,nbsp;cylindrical, jointed, ultimate twigs as those of Schenk�s plant, but thenbsp;interuodes are much shorter. The leaves when seen are always verynbsp;slightly prolonged above the joints, one being on each joint. But in somenbsp;twigs on many of the joints no leaves appear, as on the main stem in PI.nbsp;CXI, Fig. 2, and on many of the joints of PI. CXII, Fig. 5; when presentnbsp;they are often barely visible. The joints are generally marked by strongnbsp;constrictions, and many of them simply show a deeply sunken line, whichnbsp;runs across the stem more or less obliquely, generally with a downwardnbsp;bend towards the middle. It is evident that the ultimate twigs played thenbsp;part of leaves. Only in the older and larger stems do we see any woodynbsp;axis, and this is always proportionally very small considering the diameternbsp;of the twigs. The joints are placed very close together, differing in thisnbsp;point markedly from F. FEoheneggeri. The epidermis is very dense andnbsp;strong, and it is owing to it that the twigs are often found well preserved.

The ultimate twigs were deciduous, and it is a rare thing to find any of them attached to stems. They usually appear as detached fragments.

Multitudes of these fragments occur in the layer mentioned before, and they formed a considerable portion originally of the stratum They occurnbsp;here with Dioonites Buchianus, Brachjphjllum crassicaule, Williamsonia Vir-giniensis, Baieropsis pluripartita, etc. Here again we find a remarkable casenbsp;of isolation.*

Trees or shrubs, with limbs and twigs branching in an irregularly pinnate manner; leaves very short, spirally arranged, densely crowded,nbsp;and touching by their broadened bases; when living probably fleshy andnbsp;pyramidal, curved upwards, or by mutual pressure acquiring a pentagonalnbsp;or hexagonal form, and projecting in the form of a very short nippleshaped boss, persisting for a long time; when old and on thickenednbsp;branches dilated into a shield-shaped form; scars left by the fall of thenbsp;leaves erect, rhombic in form, contiguous, and marked in the middle by anbsp;vascular cicatrix.

The above is the description of the genus given by Schimper, excluding the form of Pachgphyllum Saporta, Bagiopliythmi Heer, formerly included in the genus by Brongniart. He goes'on to say that the leaves are very short, flesliy, and shaped like a nipple, which may be either straightnbsp;or curved upwards, being enlarged and touching the adjacent ones at base.nbsp;With age, and in consequence of its dilation, the nipple-shaped projectionnbsp;disappears almost wholly, and the leaves resemble pentagonal or hexagonalnbsp;cushions, which surround the branch like a cuirass. After the fall ofnbsp;these singular leaves the branches are covered with rhomboidal scars likenbsp;those of Lejndodendron.

This description in its essential points agrees better with certain of the Potomac plants than that of any other known fossils. Tlie Potomacnbsp;fossils show mostly only the scars left after the fall of the leaves, and theynbsp;do not have the vascular cicatrix in their center, but in all other respectsnbsp;these scars are exactly like those of Brachjphyllum. The peculiar mode ofnbsp;branching of this genus is well shown in the fossils now in question. Innbsp;the shape of the leaf-scars and in the arrangement of the branches, as wellnbsp;f)s in their form, some of the Potomac fossils are much like Schimper�s

genus EcJiinostrobiis. Again, in many points they are a good deal like Saporta�s genus Falaiocyparis, hut in this latter the leaves are decussate,nbsp;while in the Potomac plants they are more numerous and spirally arranged.nbsp;It is possible that the Potomac fossils belong to a generalized type alliednbsp;to Ecliinostrohus and Paloeocyparis, but standing nearest to Bracliypliyllumnbsp;It seems best to place them provisionally in this last genus.

Plate C, Pig. 4; Plate CIX, Figs. 1-7; Plate CX, Figs. 1-3; Plate CXI, Figs. 6, 7; Plate CXII, Figs.

Trees with large branches, irregularly pinnate; on the penultimate twigs the ultimate branches lower and next to the main branch subdividenbsp;pinnately into branches; those higher are unbranched and simple; ultimatenbsp;branches vary in numbers and closeness, sometimes few and remote, andnbsp;again crowded, contiguous, almost touching; towards the summit of thenbsp;penultimate branches the ultimate ones become much crowded and grownbsp;gradually shorter, are cylindrical, and taper gradually to an obtuse point;nbsp;leaf-scars of young leaves elliptical in shape, slightly prolonged in thenbsp;direction of the axes of the stems, and such leaves seem to have beennbsp;fleshy, slightly convex, and with a free tip slightly keeled in the uppernbsp;half; with age the leaves become broader and more convex, being broadlynbsp;elliptical, almost circular, and they leave similar scars after their fall;nbsp;when crowded and dilated with age the leaves and leaf-scars are sub-rhombic or rhombic in shape ; the surface of the leaves, which is very rarelynbsp;preserved, shows fine tubercles or dots, arranged in curving lines parallelnbsp;to their margins and converging towards their tips; cones small, globular,nbsp;or subelliptical in shape, attached laterally to the penultimate twigs, takingnbsp;the place of ultimate branches; scales numerous, spirally arranged, touching, shape not made out, but probably with age rhombic and polygonal.

Localities: Entrance to Trent�s Reach; 72d mile-post, near Brooke; fishing hut above Dutch Gap Canal.

Fragments of this plant are abundant at the first-named locality in the same stratum witli Frenelopsis parceramosa, etc., and are rather rare at thenbsp;other localities. Most of the specimens showing scars of leaves occur here.

PI. CX gives a large imprint of a decorticated branch found at the fishing hut above the canal. The specimen appears to have been much maceratednbsp;before entombment, so that the stone shows only the outline of the twigs,nbsp;all traces of leaves and their scars having been removed. The imprint ofnbsp;the comparatively small woody axes and of the apparently succulent matter surrounding them is all that is shown. The most common specimensnbsp;found at the entrance to Trent�s Reach are the terminal portions of thenbsp;penultimate twigs. Several good specimens were obtained at the 72d milepost. The specimens given in PI. CXII, Figs. 6-8, occur here. This isnbsp;another of the connecting links between tlie floras of the 72d mile-post andnbsp;Dutch Gap.

The views of Heer and Saporta differ mucn as to the character of the cones of Brachyphyllum. Heer ^ depicts a twig of what he calls BracJiy-pJiyllum insigne. This bears two cones. These he describes as subglobose,nbsp;with numerous spirally arranged, approximate, woody hexagonal peltatenbsp;scales, with a round depression in the center, This description appliesnbsp;partly to the macerated cone of B. crassicaule, given in PI CIX, Fig. 6, butnbsp;the obscure rounded markings on this appear to be not scales but tlie scarsnbsp;left by them. This, the only cone found attached to twigs with the character of Brachyjihylltim, is unfortunately too poorly preserved to throw any lightnbsp;on the character of the cones of this group. This cone seems to be attachednbsp;by a short branch to the under side of the twig, and hence it is partly overlapped by this.

Saporta ^ gives figures and descriptions of numerous specimens of BrachyphyHum found in France. On page 319, after noticing Heer�s conclusions, he says that the forms of Brachyphyllum presented at the upper extremities of their branchlets small or medium-sized ovoid or oblong cones, thatnbsp;were, according to the species, persistent or caducous. The cones were composed of numerous scales, arranged spirally, closely imbricated and ap-pressed, terminated by an apophysial prolongation, lanceolate in shape,nbsp;thickened, keeled on the back, and more rarely by means of an apophysisnbsp;dilated into a rhomboidal more or less developed cushion. Fie thinks tliat

� Flor. Foss. Arctica, vol. 4, pt. 2, Beitriige ziir Jura-Flora Ostsib., etc., PI, XIII, Pig. 9.

Heer�s plant was not Braclit/phyllum, but one resembling it, and that the specimen was too imperfect to decide the matter. At the entrance ofnbsp;Trent�s Reach a number of specimens of well-preserved cones are foundnbsp;with the twigs of Brachyphylluni. These agree closely with those assignednbsp;by Saporta to Brachyphylluni, and will be described further on. On thenbsp;whole, the evidence seems to indicate that Saporta�s description of the conesnbsp;of this genus is the more nearly correct one.

Brachyphyllum crassicaule is a good deal like B. Moreaiianum, Brongn., at least in some of its forms. (See Pal. Fran^aise, Veg�taux, vol. 3, PI.nbsp;CLXVI, Fig. 1; PI. CLXVII, Fig. 1.)

Twigs branching sparingly and dichotomously; leaves and leaf-scars elliptical to subrhombic, with the longer dimensions in the direction of thenbsp;length of the twigs; leaves convex, spirally arranged, showing a keel innbsp;their upper portions, closely appressed, contiguous, prolonged very slightlynbsp;at the tips, branches cylindrical, of the same thickness throughout; so farnbsp;as can be seen about 4�� in diameter.

This plant, found sparingly near Telegraph Station, differs from B. crassicaule in the comparatively slender, strictly cylindrical branches,nbsp;which show no tapering, subdivide very rarely, and then in a dichotomousnbsp;manner, and also in the regular shape of the leaves. In its general aspectnbsp;this fossil is a good deal like Cyparissidimn. It is also a good deal likenbsp;some of the forms of Brachyphyllum gracile. (See Pal. Fran^aise, V�g�taux,nbsp;vol. 3, PI. CLXVIII, Fig. 2; PI CLXX, Figs. 4, 5.)

Cone broadly oblong, widest near the top, length 20��, maximum width 15��, attached to the summit of a short branch, narrowed slightlynbsp;and gradually toward the base, showing at the summit a slight nipple ornbsp;boss-like projection; scales numerous, spirally arranged, closely appressed,

�and partly imbricated, convex, broadly elliptical to subrhombic, and slightly prolonged at their summits into acute tips.

These cones are found associated with the branches of Brachypliyllum crassicaule. They may belong to this species, or to some other conifer.nbsp;They agree pretty well in shape with the macerated cone given in PI.nbsp;CIX, Fig. 6. It is obviously a cone of the same type with those describednbsp;by Saporta as associated with the French specimens of Brachyphyllum. Itnbsp;agrees best with the cones of B. grac�l� Brongniart, but does not seem tonbsp;be identical with them.

Cone small, broadly oblong I, length not made out, as the basal portion is wanting, width 10��; scales numerous, closely appressed, partly imbricated, spirally arranged, thick and convex, in shape broadly ellipticalnbsp;to subrhombic, acute at the tips.

These cones occur with those of the preceding species and are more common than the latter. They seem to belong to a distinct species. Innbsp;the rounded shape and in the size they come nearer than any of the previously described ones to what Saporta thought was the male ament of B.nbsp;gracile Brong. It resembles in some points that shown in Pal. Francjaise,nbsp;V�g�taux, vol. 3, PI. CLXXI, Fig. 9. It maybe the male ament of B. crassicaule, although apparently rather large for that.

This is a small fragment of a cone found at the entrance to Trent�s Reach with the two last-described species. It is too imperfect to admit ofnbsp;description, the margins being in no place preserved, and the surface showing only subrhombic scars with depressed points in the center. Thesenbsp;scars seem to be those left by the scales of the cones.

A number of aments of conifers were found at the 72d mile-post, near Brooke, and elsewhere, whose species can not be determined. Theynbsp;appear to be male aments, possibly in some cases of Brachyphyllmi, butnbsp;certainly of some conifer. They usually occur together in large numbers,nbsp;as if coming from plants near by. These will be designated as (a), (amp;),nbsp;(c), etc. These aments resemble somewhat Heer�s genus Elatides.

Male (?) aments ovate to oblong in shape, small, subacute at their tips ; scales numerous, broadly elliptical, prolonged slightly into an acute tip,nbsp;spirally arranged, thin, close appressed, slightly imbricated, forming a thinnbsp;flat ament that leaves only a slight imprint; length of ament about 9��,nbsp;and width about 4quot;��.

Some fragments of shale for the space of several inches are covered more or less thickly with these aments, which evidently fell from plantsnbsp;not far distant. The shape and size of the scales and aments of thisnbsp;species agree pretty well with some of the strobiles supposed by Saportanbsp;to be male aments of species of BrachypJiyllmn}

Aments very small, broadly ovate, obtuse or acute at summit, sometimes attached to short pedicels ; size about three by six millimeters; scales very thin, close appressed, slightly imbricated, numerous, spirally arranged,nbsp;in shape broadly elliptical to subrhombic, with a slight prolongation intonbsp;acute tips.

The imprints are quite thickly scattered on some few fragments of shale, but are not so numerous as those of species (a). The cones arenbsp;smaller than those of {a).

' Compare Pal. Praugaise, V�g�taux, vol. 3, PI. CLXVII, Fig. 3, of the strobile of B. Moreauaniim Brongn.

Aments globose or bi�oadly oblong, very small and varying in size, the largest being five by three millimeters ; scales arranged as in species (a)nbsp;and (b), thin, subacute at their tips, closely appressed, minute, narrowlynbsp;elliptical in shape, numerous, and spirally arranged, somewhat imbricated.

They occur on a few pieces of shale in considerable numbers crowded together; seem to be different from species (a) and (b) in the smaller andnbsp;more variable size and the more rounded form and in the narrowly ellipticnbsp;shape of the scales.

Aments mostly ovate, sometimes elliptical, varying somewhat in size, averaging five by three millimeters, broadest at base and narrowed above tonbsp;an acute tip; scales in number and arrangement as in the preceding species,nbsp;in shape broadly elliptical to ovate, prolonged at the summit to a verynbsp;short acute tip.

This station is on the Alexandria and Fredericksburg portion of the Atlantic Coast Line Railroad, midway between Quantico and Powell�snbsp;Creeks. The aments are found in the shale in a cut a little north of thenbsp;station. They occur crowded in considerable numbers on the surface of anbsp;few specimens of the rock. No prolonged search was made here, as therenbsp;did not seem to be any prospect of finding good material. With thesenbsp;were found a few obscure imprints of some conifer with acicular leaves.

An ament, elongate-oblong in form, very narrow in proportion to its length, with numerous chaffy scales imbricated on a slender axis, incurved and spoon-shaped.

Only one specimen of this fossil was found. It seems to be the male ament of some conifer, possibly of some one described under anothernbsp;name. Fig. T** represents one of the scales flattened out by pressure onnbsp;the surface of the clay. Fig. represents the shape of the enlarged scalesnbsp;as they were attached to the axis.

Fig. 8 represents small catkins, that occur rarely, grouped together in large numbers on the surface of some portions of the clay at the 72d milepost. Where found they cover the surface confusedly, as if they hadnbsp;floated in numbers on the surface of the water. They occur only in smallnbsp;bits, none showing the entire length. They were linear in shape. Nonbsp;conjecture can be made as to the species of tree from which they come.

�Strobile stipitate, very long, with scales that are loosely imbricated, narrowed at base, and have the upper margin crenulate ;nbsp;nbsp;nbsp;nbsp;*nbsp;nbsp;nbsp;nbsp;*nbsp;nbsp;nbsp;nbsp;* leaves

needle-shaped, fasciculated on shortened branches.� This is Heer�s description of the genus formed to contain peculiar Jurassic plants from eastern Siberia. He says of Leptostrohus rigida^ that the leaves are 2�� wide, verynbsp;long:, with two verv distinct nerves, which sometimes show between them-selves some very fine striae (see PI. VII, Fig. 11'�). Some of the fragmentsnbsp;of leaves that he saw were lO.b�� long with the ends not present. If wenbsp;modify Heer�s description so as to make it read: leaves needle-shaped, verynbsp;long, 2quot;�� and under in width, scattered on the larger or principal stemsnbsp;and grouped in bundles on the ends of short twigs, attached directly to thenbsp;stems, nerves slender and parallel, we shall be able to include in this genusnbsp;certain remarkable conifers found in the Potomac strata. These Potomacnbsp;fossils are a good deal like Sclmolepis Fr. Braun, but the leaf of this latter had only one nerve.

' Flor. Foss. Arotica, vol. 6, pt. 1, Nacht-riigo zur. Jura-Flora Siberiens, p. 25.

Plate Cl, Figs. 2, 3; Plate CII, Figs. 1-4; Plate CIII, Figs. 6-12; Plate CIV, Fig. 6.

Trees or shrubs with stout and long primary leafy branches, which contain the leaves attached singly and scattered along the stem, as nownbsp;seen attached to the under surface or to the sides of the stems, but mostnbsp;probably originally found spirally arranged and attached to the stems onnbsp;all sides. The primary leafy branches have lateral and terminal short shoots,nbsp;on the ends of which the leaves are arranged in tufts; leaves very longnbsp;and narrowly linear or needle-shaped, with their extremities in no casenbsp;seen, attached by the entire bases, not narrowed; nerves several, parallel,nbsp;slender, and obscure.

Localities: Fishing hut above Dutch Gap Canal; Fredericksburg; 72d mile-post and bank near Brooke; hill-side near Potomac Run.

The plant is not uncommon at any of the localities. It is most abundant at the fishing hut above Dutch Gap Canal, where all the forms depicted on PI. CII occur. The leaves occur, as elsewhere, most commonly detached. They seem to be quite deciduous, especially on thenbsp;older and larger stems. All the specimens found have suffered from maceration and transportation in water, and hence the present mode of arrangement of the leaves in the comparatively few cases where they are foundnbsp;attached does not give an accurate picture of their original condition.nbsp;The leaves in tufts at the ends of the short shoots may represent all thatnbsp;were originally present, or they may be only the younger last-formed ones,nbsp;the older ones lower on the twigs having fallen off.

This latter is probably the true state of the case. At any rate, these short shoots seem to be growths from lateral buds, perhaps annually formed.nbsp;Neither on these nor on the longer main stems are any scars left by fallennbsp;leaves to be seen, but this does not prove that they were not present, fornbsp;in all cases the naked portions have lost their epidermis and suffered anbsp;good deal from maceration. They are decorticated and reduced to thenbsp;woody fiber, or show only imprints of this. The leaves as now seen on thenbsp;older and larger stems seem to be all attached laterally, or to the ends ofnbsp;the stems or to the under surface. This is probably due to the accidents

of preservation. The leaves on the upper surface, after the settling of the twig on the bottom, were most exposed to the action of the water and werenbsp;removed, while those that were attached to the under surface, being heldnbsp;in place by the pressure of the superincumbent stem, were retained. Mostnbsp;of the leaves that appear to be attached to the sides of the stems no doubtnbsp;are really attached to their under surface. This seems to be the case innbsp;PI. Cl, Fig. 2, and PI. CII, Fig. 3. The ends of the large stems in thesenbsp;figures are broken off. It is, then, most probable that the leaves were scattered spirally around the larger stems. The leaves seem to have beennbsp;attached by their entire unnarrowed bases and to have been directednbsp;upwards towards the summits of the stems. Hence we find them sometimes curved at base as Heer^ has depicted, but I have seen none so muchnbsp;bent or so regulaidy, as those of Heer.

The nerves are very obscure, and the leaves, even the best preserved, rarely show any traces of them, for they seem to have been slender andnbsp;immersed in the leaf-substance. Generally only fine striae are visible onnbsp;them, even with the help of a lens. They seem to be about four in numbernbsp;and parallel. No difference in strength was noted, as Heer intimated. Thenbsp;length of some of the leaves must have been very considerable, for somenbsp;fragments, with both the base and summit missing, were as much as 15��nbsp;long. In PI. CHI, Figs. 6, 8, 9, are given some fragments of leaves fromnbsp;the 72d mile-post near Brooke, where detached leaves occur on some portions of the shale in considerable numbers, crowded together or overlyingnbsp;one another. In some cases, as in 8� and 6% they show four very finenbsp;nerves. In others, as 6'^, no nerves are seen, but the leaves appear smoothnbsp;and convex from pressure. Again, in some cases, as in 6�, only one nervenbsp;is visible. Sometimes, as in O'* and 6�, the nerves vary in strength and arenbsp;vaguely shown. These differences are no doubt due to the accidents ofnbsp;preservation. Sometimes it seems that apparent nerves are longitudinalnbsp;wrinkles or folds in the leaves caused by pressure. This seems to be thenbsp;case in 6� and 6�.

On the hill-side near Potomac Run a good many detached fragments of long and very narrow leaves with four very fine nerves occur scattered

on some portions of the shale. They are shown partly in PI ClII, Figs. 10-12, and PI. CIV, Fig. 6. These were never seen certainly attached tonbsp;any stem, but their bases are sometimes well shown, looking as if theynbsp;had been attached in a clasping manner by a widened base, and in PI. CIV,nbsp;Fig. 6, the base may be seen attaclied to what seems to be a portion of thenbsp;stem. In PI. CIII, Fig. 12, two bases seem to be put together, possibly bynbsp;accident. These leaves may belong to a different species, but I place themnbsp;provisionally in the species now being described.

Leaves long and very slender, about 1�� in width, length not made out, densely crowded on the principal and longer shoots throughout their length,nbsp;grouped in bundles at the ends of the shorter lateral shoots: nerves verynbsp;slender, not well made out, apparently three in number.

Localities: Fishing hut above Dutch Gap Canal; red clay ball in the banks of Dutch Gap Canal.

This is clearly a different species from the preceding, and it is not so common. The nerves could be seen on only one specimen and that vaguely,nbsp;so that their number is not positively determined. They appear to be three,nbsp;but this may be due to the state of preservation, and the number visiblenbsp;may vary according to the condition of the fossil. It is quite possible thatnbsp;the true number may be four. The leaves are almost always seen detachednbsp;and crowded together, as if derived from the same specimen.

Strobile stipitate, with a very thick axis of inflorescence, covered by numerous small spatulate-shaped scales, that are loosely imbricated andnbsp;arranged in a spiral manner.

Only one specimen of this curious inflorescence was found, and it was too imperfect to make out clearly its character, since the rock on which thenbsp;imprint was made is a rather coarse sandstone. The specimen was evi-

dently raucli injured by maceration before it was entombed. The lower portion of the axis has lost most of its scales, while the upper portion stillnbsp;retains them. These scales, although smaller than those given by Heer fornbsp;the species examined by him, appear to more nearly resemble those of Lep-tostrohus than those of any other plant. I place it with doubt in this genus.nbsp;The cone somewhat resembles those of Heer,^ but the scales are smaller,nbsp;more numerous, and more closely placed.

The following seed have the character of the seeds described by Heer as Saniaropsis, from the Jurassic of Ust-Balei, in eastern Siberia.^ Thesenbsp;seeds Heer,� in subsequent remarks on Leptostrohus, takes to be those ofnbsp;that plant. The Potomac seed throw no additional light on the subject.nbsp;It is at least significant that they occur with leafy branches that have thenbsp;character of Leptostrohus. It will perhaps be best to distinguish thesenbsp;Potomac fossil seed as Leptostrohus (�), (amp;), etc.

Seed smooth, obovate in shape, obtusely rounded at one end, and narrowed at the other into a sort of neck; winged, with wings of the same width, except towards the neck, where it is slightly narrowed.

Seeds of this nature are sparingly found at this locality. They may be seed of one of the species of Leptostrohus found at Dutch Gap.

Seed broadly elliptical, winged; wing proportionally small and prolonged at one end into a slight point, widest in the middle, and narrowed slightly towards the extremities of the seed.

Winged seed of this nature are found sparingly here. They may be seed of Leptostrohus.

'^Flor. Foss. Arctica, vol. 4, pt. 2, Beitriige zur Jura-Flora Ostsib. etc., p. 80, et seq.

Seed oblong-elliptical, with a slight acute tip at one end and a very short stem-like prolongation at the other. Smooth, winged; wing verynbsp;large in proportion to the seed, widest in the middle and flared out there,nbsp;narrowed towards the apex and base, prolonged to a short subacute point,nbsp;and ending below in what seems to be a point of attachment to a pedicel.

This seed differs from the others in its greater size as well as that of the wing, and in the greater proportional size of the wing as comparednbsp;with the seed, also in the flaring out of the wing in its middle portion. Itnbsp;is a little like Heer�s Samaropsis rotundata. It is possible that these seednbsp;do not belong to JLeptostrohus, but to the genus next to be described, viz,nbsp;Laricopsis, for Larix has samara-like seed.

Trees or shrubs, with the penultimate twigs sending off alternately in the same plane ultimate branches; leaves thin, narrow, and thread-like,nbsp;attached by the entire base either in bundles at the same point on thenbsp;stem or scattered singly on its surface, both on the same stem, verynbsp;deciduous, the leaf-bundles leaving small scars Nerves not made outnbsp;with certainty, but apparently one for each leaf

This genus is nearer to Larix than to any other known plant, and the resemblance is sufficiently great to render it possible that it may be thenbsp;.ancestor of this genus. It should be noted that the young shoots of Larixnbsp;often have the leaves scattered singly as they occur in this genus, and it isnbsp;probable that the immature portions of Larix approach the ancestral formsnbsp;more nearly than the mature portions do. In these specimens also thenbsp;leaves appear most often to be attached laterally to the stems as now preserved, while no doubt they were originally scattered around the stem.nbsp;This appearance, as in the case of Leptostrobus, is doubtless due to thenbsp;accidents of preservation. No nerves could be made out with certainty.nbsp;The leaves are very narrow, being sometimes like hairs.

Plate CII, Pigs. 7, 8; Plate CIII, Figs. 2, 3; Plate CLXV, Fig. 4; Plate CLXVIII, PigA 5,6.

Leafy stems comparatively very stout, branching rarely, with the ultimate branches in the same plane and alternate; leaves narrow, aboutnbsp;.5�� or under in width, very long in proportion; portions seen are overnbsp;long and not entire, grouped occasionally in bundles as in Larix, morenbsp;commonly scattered singly and attached by the unnarrowed bases, flat andnbsp;thin, deciduous on the older branches; nerves not certainly made out,nbsp;apparently one for each leaf.

The plant is rather rare, and is generally found in a very fragmentary state or in the form of detached leaves. The removal of the leaf-bundlesnbsp;leaves sometimes quite distinct dot-like scars on the upper surface of thenbsp;stems. Considering the narrowness of the leaves the stems are remarkablynbsp;thick. Owing to the crossing of the leaves in superposition they oftennbsp;look as if they split into branches, and then they remind one strongly ofnbsp;Heers genus Phcenicopsis, but they certainly never fork.

Twigs slender, branching sparingly; leaves exceedingly narrow and hair-like, entire length not seen, but certainfy equaling 3*��, thin, flat,nbsp;scattered over the surface of the stems or grouped in bundles; nerves notnbsp;seen.

Localities: Fishing hut above Dutch Gap Canal; entrance to Trent�s Reach; rare.

These leaves often do not surpass .2�� in width. As in the case of the preceding species, they are always broken off towards the tips, so thatnbsp;their true length can not be made out. The leaves as now seen are allnbsp;attached to the sides of the stems apparently, but this is no doubt due tonbsp;the fact that they, in many cases at least, come from the under sides ofnbsp;the stems, being held in place by the superposition of the latter. Thenbsp;grouping of the leaves in bundles occurs irregularly and rather rarely.

Possibly these specimens may be the narrower leaves on forms of the preceding species, but this is hardly probable. It is rare, but more common than the preceding species.

Twigs slender, branching freely; leaves distributed and attached as in the preceding two species, thin, flat, wide in proportion to their length,nbsp;short, acute at the tips; nerves not seen; length of leaves and littlenbsp;more, width 8��, crowded on the younger branches, deciduous when old.

This plant is quite rare. The leaves are, in proportion to their length, much wider than those of the two preceding species. Fig. 5 presents twonbsp;lower branches on the right-hand side that are entirely deprived of theirnbsp;leaves. The leaves of this species look something like those of Heer�snbsp;genus Inolepis.

Small trees, with leaves linear or lanceolate, in two rows, either opposite or alternate, flat, decurrent at base, without a midrib, but marked longitudinally on the lower side, on each side of the central line of thenbsp;leaf, by a narrow sunken band.

This genus has not furnished to the Potomac flora any considerable element, since the two species found are quite rare.

Stems slender; leaves subopposite, linear, narrowed gradually to the base and apex, at the apex prolonged into a short spinous tip, attached bynbsp;a short slightly twisted footstalk to the margins of the stems or slightlynbsp;within them, slightly decurrent; midnerve not apparent. The leaves havenbsp;on each side of their axial line a strong cord-like line running through thenbsp;leaf nearly parallel, converging at the base and apex, and seeming to be

imprints made by the two medial depressed lines of the leaf; leaves rather remote, flat, coriaceous, and persistent.

This plant is quite different from the species of CepJialotaxopsis and Nageiopsis found in the Potomac flora. The leaves were leathery andnbsp;durable, and marked by two proiuinent cord-like ridges in the center, whichnbsp;do not seem to have been nerves.

Stems of ultimate twigs slender; leaves coriaceous, distichous, approximate, spreading, attached by a broad base to the margins of the twigs, or somewhat within the margins, slightly decurrent, linear, falcate, acute,nbsp;prolonged at the summit into a short spinous tip. Marked in the medialnbsp;line with two strong parallel lines.

This plant is a good deal like T. parvifolia, Heer, as given in Flor. Foss. Arctica, vol. 3, pt. 2, PI. XVII, Figs. 1, 2.

Trees or shrubs, with fruit probably in the form of drupaceous and nut-like seed, branching copiously, with branches umbellately arranged ornbsp;alternate in the same plane, often opposite from paired terminal buds;nbsp;stems comparatively very stout, rigid, and woody; leaves distichous, varying a good deal in size, flat, linear, thick and leathery, persistent, attachednbsp;by very short slightly twisted footstalks to the sides of the stems ornbsp;slightly within the margins, prolonged at the apex into a short spinousnbsp;tip, with a single flat broad midnerve, which on the lower side of the leafnbsp;is bordered on each side like Torreya by a sunken line.

This is a very important genus in the Potomac flora, on account of both the number of species and the great number of individuals in some ofnbsp;the species. The genus is one of the most characteristic types of the Potomac vegetation. It is very near to Cephalotaxus, but does not appear to be

identical with it. It rather seems to be a composite type, uniting some of the features of Gephalotaxus, Torreya, and perhaps Taxus. A common modenbsp;of growth of the branches seems to have been by a terminal bud with opposite buds, one being on each side of the terminal one, all being covered withnbsp;scales, which, as in Gephalotaxus, leave sometimes distinct scars at the base ofnbsp;the shoots of annual growth.

No fruit has been found attached to the leafy twigs of these plants, hence its nature has not with certainty been determined, but certain nutlike fruits have been found in company with the leaves which most probably belong to .this genus.

Plate CIV, Figs. 4, 5; Plate CV, Figs. 1, 3, 4; Plate CVI, Figs. 1, 3; Plate CVII, Figs, 1, 8, 4; Plate fnbsp;nbsp;nbsp;nbsp;CVIII, Figs. 1, 3, 4.

A tree or large shrub, with stout limbs, so far as seen, branching sparingly, the branches being in the same plane and remote, opposite or alternate, the ultimate twigs showing sometimes at their bases scars of the bud-scales ; leaves variable in size, attaining a maximum length of 6� and a maximum width of 5��; subspirally arranged, that is, attached mostly tonbsp;the sides of the twigs, but sometimes somewhat within the margins andnbsp;slightly on the upper and lower surfaces; attached by short slightly twistednbsp;footstalks in two rows in the same plane, subopposite or alternate, rathernbsp;remote, with the ultimate twigs terminated abruptly by a leaf; the leavesnbsp;very thick and leathery, persistent, and very durable, widest near the basenbsp;and generally abruptly rounded off there, more rarely tapering graduallynbsp;to the base, gradually narrowing towards the apex, where they terminatenbsp;in a spinous or mucronate point; the leaves (see PI. CV, Fig. 1) belownbsp;and near the shoots of annual growth sometimes unusually small; midribnbsp;broad, flat, distinct, with a narrow sunken line on each side.

Localities: Fishing hut above Dutch Gap Canal, rare; Fredericksburg, very common.

This is one of the most abundant plants at Fredericksburg, where many well-preserved specimens occurred. The growth of the twigs seemsnbsp;often to have been made by a terminal bud flanked by two opposite lat-

eral ones, and these seem to have had persistent bud-scales, which have sometimes left quite distinct scars, as in PI. CV, Fig. 1.

Owing to the leathery character and great durability of the leaves, they may often be found as perfectly pi�eserved as if they had been pressednbsp;in a herbarium, even sometimes having a greenish color. They thennbsp;show the minutest details of their structure. The spiny tijD at the ends ofnbsp;the leaves seems to be the prolongation of the midrib beyond the leafnbsp;This tip, however, is not generally preserved. The thick character of thenbsp;leaves has caused them in drying to wrinkle transversely, as in PI. CVI,nbsp;Fig. 1�. The leaves are notably thick and prominent. As shown in PI.nbsp;CV, Fig. 2, the ultimate twigs are terminated by a leaf in a manner similarnbsp;to cycads. The midrib has two depressed lines running very close to itnbsp;that leave in some cases two imprints looking like two parallel nerves, asnbsp;in PL CVIII, Fig. 4, and PI. CIV, Fig 5. These remind one of the twonbsp;imprints seen in Torreya. The variation in the size of the leaves does notnbsp;surpass that seen in Cephalotaxus drupacea, which this plant closely resembles. The bud-scales seem to have been persistent for some time.

Plate CIV, Figs. 2, 3; Plate CVI, Figs. 2, 4; Plate CVII, Fig. 3; Plate CVIII, Pig. 2.

Tree or shrub, with stout branches in whorls or scattered alternately, and in the same plane; bud-scales persistent at the bases of the shoots ofnbsp;annual growth; leaves comparatively thin, narrow, tapering gradually tonbsp;the base and apex, insertion and arrangement of the leaves as in C. magni-folia; the leaves have a maximum length of and a maximum width of

This plant is much like G. magnifolia, but it is much more copiousl}quot; branched, the leaves are narrower in proportion to their length, have anbsp;thinner texture, and a proportionally narrower midrib. It is rather morenbsp;abundant at Fredericksburg than C. magnifolia. It may possibly be a formnbsp;of C magnifolia, but the facies is constant and different from that of thisnbsp;species. The tendency to a whorled grouping of the branches is marked.nbsp;A common mode of arrangement is that given in PI. CVII, Fig. 3, PI. CIV,

Fig. 2. The branches are now by pressure brought into one plane. In PI. CVIII, Fig. 2, the right-hand lateral branch has been torn off. In PI.nbsp;CVI, Fig. 2, they appear to have been pinnately arranged, a mode not sonbsp;common as the umbellate one.nbsp;originally to have belonged to the same branch.

Trees or shrubs, with ultimate branches, so far as seen, alternate and strictly in one plane; leaves thick and leathery, attached and arranged asnbsp;in the preceding species, narrowly oblong to narrowly elliptical, mostlynbsp;narrowed gradually at the base and apex, maximum dimensions 21�� bynbsp;3��, average dimensions 13�� by 2��, short in proportion to the width;nbsp;midnerve slender.

Localities: Fishing hut above Dutch Gap Canal; Fredericksburg; road-side near Potomac Run ; rai�e.

PI. CV, Fig. 3, a specimen from Fredericksburg, gives the largest leaves seen. Only small fragments of ultimate branches were found. The leavesnbsp;in proportion to their size are remarkably thick and leathery.

Tree or shrub, copiously branching, with branches alternate, slender, all in one plane; leaves arranged and attached as in the preceding species,nbsp;very small, average dimensions by 7��, leaf-substance thin, in shapenbsp;narrowly oblong to narrowly elliptical, tapering gradually to the base andnbsp;apex; midnerve slender.

This plant is quite rare, and is the smallest of the genus. The leaves on the ultimate twigs towards the summit of the branches are very minute,nbsp;as on the uppermost branch on the left hand in PI. CIX, Fig. 9, from thenbsp;Dutch Gap locality. The midnerve, owing to its slenderness, is generallynbsp;not visible.

Trees or shrubs, copiously branching, with principal stems or branches proportionally strong, cylindrical, rigid, sending off thickly placed, long,nbsp;slender, cord-like, ultimate twigs, all in the same plane and spreading widely;nbsp;the ultimate twigs leave the penultimate ones under a very acute angle andnbsp;show a tendency to a fastigiate grouping; cones mostly broadly oblong,nbsp;rarely globular, obtuse and rounded at base and apex, average dimensionsnbsp;10�� by 14��, attached singly on the summit of short lateral branches andnbsp;placed on the lower portions of the leafy stems and branches, the twig withnbsp;its cone representing the branching leafy twigs which occur higher up;nbsp;scales of the cones woody, thick, wedge-shaped in the basal portions,nbsp;expanded at the free ends, and probably shield-shaped, numerous, spirallynbsp;placed, attached at a large angle, the middle ones being nearly or quite atnbsp;a right angle with the axis, close appressed, opening with age; seed undernbsp;each scale one, elliptical in shape, smooth and bony in texture, averagenbsp;dimensions 1�� by 2.5��; leafy branches ending abruptly in an ultimatenbsp;twig similar to those sent off pinnately and alternately lower down ; leavesnbsp;very thin and scale-like, elliptical, rhombic, or oblong, with varying agenbsp;changing their shape, the rhombic forms representing the oldest and mostnbsp;crowded leaves, slightly keeled on the back, spirally arranged.

As now found, owing to maceration, the leaves are rarely visible or appear very indistinct. The upper or free surface of the scales of thenbsp;cones was in no case seen sufficiently well preserved and so presented asnbsp;to show clearly its original character. This surface seems to have beennbsp;expanded something like the similarly placed part in the scales of Sequoia.nbsp;The shape of the cone also is a good deal like that of the cone of thatnbsp;genus, but the leaves and the number of seed under the scales differ. Thenbsp;scales of Athrotaxopsis are wedge-shaped, thick, and woody. In a numbernbsp;of cases they were found sufficiently well preserved to permit one to separate them from the cone, and to pick out the comparatively large seed,nbsp;which were very well preserved. The cones are comparatively quite smallnbsp;in size, and are found on the lower portions of leafy principal twigs. Innbsp;some cases, where the cones are numerous, the branch seems to have borne

no leafy twigs, as in the specimens given in PI. CXVI, Figs. 1, 2. The cones when unripe are compact, with close-appressed scales, hut with agenbsp;the scales diverge.

Heer^ describes his genus Cyparissidium as having an oval strobile, furnished with numerous scales, which are spirally arranged on the axis,nbsp;imbricated, coriaceous, and rounded, loosely spreading at the apex, mucro-nate, etc.; seed one under each scale and rounded ? ; leaves alternate, imbricated, and appressed. Heer bases his conclusions as to tlie character of thenbsp;seed on the imprint of a rounded object under a scale similar to those thatnbsp;he attributes to Cyparissidium (See PI. XIX, Fig. 11.)

While Athrotaxopsis has a number of the characters of Cyparissidium, the differences are too important to allow its being united with the latternbsp;genus; the character of the cone is essentially different. Athrotaxopsis innbsp;many features, both of the foliage and the cones, is strikingly like the living genus Athrotaxis, and perhaps may be regarded as an ancestral form ofnbsp;this genus. The main distmction is in the single seed under each scale. Itnbsp;has also, in the character of the leaves and branches, points in common withnbsp;Echinostrobus and Saporta�s genus Palceocyparis. It is evidently a comprehensive type. The great length and slendeniess of the ultimate twigs makenbsp;it probable that they were pendulous.

Trees or shrubs, with strong principal branches, bearing cones on the lower portions, and in the upper portions leafy branchlets alone; stems seennbsp;P� thick, with a length of 30�'quot; and an expanse of over 25�'quot;, the terminalnbsp;portions not being preserved. Cones as given in the generic description,nbsp;leafy stems copiously branched in an alternate manner, the branches beingnbsp;crowded and all in the same plane. The ultimate twigs are long, comparatively strong, and cord-like, and were probably pendulous, mostly unbranched, or sometimes dividing dichotomously; leaves close appressed,nbsp;elliptical when young and acute at their tips; rhombic when old, andnbsp;crowded, thin, slightly keeled on the summit.

At the latter place the plant is rare, but at the former it is quite common, being in one layer one of the most common plants. It occurs here sometimes in very large specimens. The fine form figured in PL CXIV,nbsp;Fig. 1, is a part of a specimen which, although still only a fragment of anbsp;branch, was considerably larger than the part figured. Most of the largenbsp;specimens have suffered so much from the action of water before entombment that they are decorticated and have lost their leaves.

Plate CXIV, Figs. 4, 5; Plate CXV, Fig. 4; Plate CXVJ, Fig. 6; Plate CXVII, Fig. 2.

Small trees or shrubs, with comparatively very slender stems, branching copiously and mostly at short intervals; branches alternate and in the same plane, ultimate branches short, slender, thread-like, with an ultimatenbsp;branch terminating the penultimate branches, the ultimate twigs simple ornbsp;rarely dichotomous; leaves arranged spirally, close appressed, keelednbsp;slightly at the tips, elliptical to rhombic in shape, acute.

At the latter place the plant is rare, while it is not uncommon at the former. This form is characterized by the narrowness and the shortness ofnbsp;the ultimate branches. They are usually numerous and closely placed.nbsp;The leaves are rarely preserved, and they sometimes show a faint keel atnbsp;their tips, as in PI. CXVII, Fig. 2^

Plate CXIII, Figs. 5, 6; Plate CXV, Fig. 2 ; Plate CXVI, Fig. 5; Plate CXVII, Fig. 6; Plate CXXXV

Trees or shrubs, the leafy branches being very long and with slender woody axes, spreading widely, sparingly branched, branches in one plane;nbsp;the ultimate twigs alternate, remote, very long and cord-like, probablynbsp;pendulous, unbranched or rarely dichotomous; leaves quite thick (comparatively), keeled, elliptical to subrhombic, acute to obtuse, the lateralnbsp;ones often rather obtuse and divergent from the stem, cones oblong, sometimes from distortion made more or less globular in form, comparatively

large, being 14�� by 11�� on an average, scales and other parts as in the generic description.

Localities: Hill-side near Potomac Run; entrance to Trent�s Reach; banks of Dutch Gap Canal; fishing hut above the canal.

This plant is very common in large specimens at the first and last named localities. At the Potomac Run locality, on the hill-side in thenbsp;woods, it is, next to the ferns, the most common plant, but it is not found onnbsp;the road-side only a few hundred feet away. The fine specimen, PI. CXV,nbsp;Fig. 2, comes from the fishing hut. The lower detached fragments werenbsp;once no doubt attached to the same stem with the upper portion. Thisnbsp;figure shows well the characteristic mode of branching of the species andnbsp;the wide spread of the twigs. This species shows a mode of preservationnbsp;of the twigs common in this but rare in the others. In it the leaves onnbsp;the upper face of the older stems have fallen off, exposing the slendernbsp;woody axis, whereas on the ultimate youngest twigs all the leaves are preserved. The cone, PI. CXVII, Fig. 6, from Potomac Run, is no doubtnbsp;globular in form on account of distortion, being compressed in the direction of its length. These cones are larger than those of A. grandis. Platenbsp;CXXXV, Fig. 15, gives one of the largest size.

Small trees or shrubs, copiously branching, with branches all in one plane, comparatively stout, rigid, and mostly long, cylindrical in shape;nbsp;ultimate twigs mostly simple; leaves very thick, prominent, horny innbsp;texture, with strong keel, arranged as in the preceding species, elliptical tonbsp;rhombic in shape, very durable, dropping off with increasing age; conesnbsp;not seen.

This plant is one of the most common ones in the banks of Dutch Gap Canal. It occurs, however, in a very fragmentary condition. It isnbsp;characterized bv the thickness of the leaves.

Leafy branches, with keeled stems which were apparently succulent, branching dichotomously ; leaves remotely placed, alternate to subopposite,nbsp;widest near the base, decurrent, narrowly linear, acute, varying in lengthnbsp;considerably, attaining the maximum dimensions of 3.5�� in length andnbsp;2�� in width, margins of the leaves apparently thickened from being rollednbsp;slightly, obliquely inserted, the longer leaves straight or slightly curvednbsp;upwards, shorter leaves (on younger branches ?) strongly falcate, all thick,nbsp;leathery, and rigid, with a midnerve that is prominent on the lower side ofnbsp;the leaves and forms a sort of keel in the longer leaves, showing a sunkennbsp;central line on the upper side of the leaves.

This plant is very rare. It is in some respects unlike the ordinary forms of Sequoia, and so strongly resembles Cycadites that for some time Inbsp;thought that it should be placed in that genus, but the finding of branchingnbsp;stems, such as are shown in PI. CXII, Fig. 9, shows that it can not benbsp;Cycadites. Perhaps it should be regarded as a new genus, but as it standsnbsp;apparently nearest to Sequoia I have placed it provisionally in that genus.nbsp;It seems to be a comprehensive form, combining the characters of Cycaditesnbsp;with those of some of the species of Podocarpus, such as P. Meyeriananbsp;Endlicher, and P. elongata E. Meyer. It is also a good deal like Taxitesnbsp;falcatus Nathorst (see Floran vid Bjuf, PI. XXII, Fig. 11). In the decurrent leaves lying strictly in one plane it resembles Sequoia. It is a goodnbsp;deal like Dawson�s Cycadites unjiga (see Cretaceous and Tertiary Flora ofnbsp;British Columbia, PI. I, Figs. 2, 2Q.

Plate CXVIII, Pigs. 1, 4; Plate CXIX, Pigs. 1-.5; Plate CXX, Figs. 7, 8; Plate CXXII, Fig. 2; Plate

Branches elongate, leaves decurrent at base, spreading, linear-lanceolate, falcate, incurved, acuminate, widest at base; one-nerved.

Localities: Fredericksburg; fisliing hut above Dutch Grap Canal; banks of Dutch Gap Canal.

This plant is quite abundant at the fishing hut in the forms with narrow leaves, such as are figured in PL CLXVII, Fig. 5. It is also common in such forms as PI. CXVIII, Fig. 4, etc. It is comparatively rarenbsp;at the other localities.

The type of Sequoia illustrated in 8. Beichenhachi is much the most common one in the Potomac flora. It is illustrated in such plants asnbsp;8. amhigua and 8. subulata. Those witli scale-shaped leaves are very cares'. Beichenhachi is the most common conifer at the fishing hut. Neaidynbsp;all the specimens have the leaves closely placed on the twigs. The twigsnbsp;branch copiously, and by their size indicate that the growth was vigorousnbsp;All the leaves are widest at base, strongly falcate and acute, decurrent atnbsp;base, with a distinct midrib, the larger leaves being acuminate. PI. CXX,nbsp;Fig. 7, shows an unusual mode of insertion of the leaves, they being atnbsp;right angles with the stem. This position seems to be assumed by thenbsp;older leaves. As a rule the younger leaves are obliquely placed andnbsp;strongly curved upwards. The scars left by the leaves after falling offnbsp;from the older twigs are obovate, rounded at the top, with a round vascularnbsp;scar at the top and a furrow running down from it (see PI. CXIX, Figs. 4,nbsp;5). Fig. 4 gives the natural size, and Fig. 5 gives the scars from anothernbsp;stem enlarged. The forms, PI. CXVIII, Fig. 1, and PL CXIX, Fig. 1,nbsp;show some differences from the Dutch Gap specimens in having the leavesnbsp;more remote and obtuse. They look something like Heer�s species S.nbsp;Smithiana. The first-named specimen shows that some of the formsnbsp;attained very considerable dimensions. In PL CXVIII, Fig. 4, and PLnbsp;CXIX, Fig. 3, at the points marked (a), we have the tips of twigs showingnbsp;a growing bud with undeveloped leaves.

Stems comparatively very stout, branching freely; leaves rather remotely placed, strongly falcate, narrowly linear, widest at base, decurrent, and united to form a narrow wing, very long and acuminate; midnerve slender.

This plant difiPers from the normal 8. Iteichenhachi in the very long and slender leaves.

Branches comparatively slender, pinnately arranged in one plane; the ultimate branches are nearly at right angles with the penultimate stems;nbsp;leaves obliquely inserted, widest at base, acuminate, very narrow, sometimes acicular, very long in proportion to their width, usually closelynbsp;placed on the ultimate twigs, more remote on the older ones, united at base.

Localities: Fishing hut above Dutch Gap Canal; Fredericksburg; near Telegraph Station.

The plant is rather common at the Dutch Gap locality, but is very rare elsewhere. PI. CXVII, Fig. 7, gives a portion of an older twig withnbsp;unusually remote and very narrow leaves. PI. CXVIII, Fig. 6, has onnbsp;the ultimate twigs closely placed leaves that are very long in proportion tonbsp;their width.

Plate CXVIII, Fig. 2; Plate CXX, Figs. 1-6; Plate CXXVII, Fig. 5; Plate CXXXII, Fig. 3.

Branches elongate, fully leaved throughout, branchlets alternately grouped; leaves decurrent, short, rather thick, falcate, incurved, acuminate,nbsp;one-nerved; strobiles globose in form; scales peltate, rather flat.

This description which Heer gives^ for his Sequoia ambigua, from the Koine beds of Greenland, and his figures agree so closely with certain ofnbsp;the Potomac conifers, that there seems to be no doubt that this plant is foundnbsp;in the Potomac flora also. It may be added, for the Potomac forms, thatnbsp;the leaves are widest at base, narrowly oblong to siibtriangular.

Localities: Fisliing hut above Dutch Gap Canal; river bank a few yards above the fishing hut; near Telegraph Station.

The plant is rather common at the first and second localities, and rare at the third. There are a few points of difference in the Kome and Potomac forms, but no greater than might be expected in the same species when

grown so far apart. The leaves of the Potomac plant are apparently not quite so thick as those from Kome and not so constantly incurved, andnbsp;they are usually more closely placed. The cones of the Potomac plantnbsp;have the free surface not so much elongated transversely, and the transversenbsp;depression on their summit is greater.

Plate CXVIII, Fig. 3; Plate CXXI, Fig. 2; Plate CXXVI, Fig. 2; Plate CXXX, Fig. 3.

Leaves coriaceous, rigid, linear, acuminate at apex, patent, straight, one-nerved, transversely very finely rugulose, not narrowed at base,nbsp;adnately long decurrent.

This description of S. rigida, given by Heer,quot;^ agrees very well with some of the Potomac conifers, the transverse rugosity alone being absent.nbsp;This, however, is accidental, and due to the accidents of preservation. Thenbsp;localities for the Potomac fossils are near Telegraph Station ; hill-side nearnbsp;Potomac Run. The form PI. CXXI, Fig. 2, is one of the most commonnbsp;plants near Telegraph Station. Heer says that this species is more commonnbsp;in the Atane than in the Kome beds. PI CXXX, Fig. 3, is a good deal likenbsp;Glyptostrobus Grcenlandicus, as given by Heer.^ He speaks of the leavesnbsp;of S. rigida as prolonged into a fine point. This feature may be seen on anbsp;number of the specimens of the Potomac fossil. It is not, however, anbsp;character that would in most cases be preserved. It is noteworthy that sonbsp;far as seen this species does not occur at Fredericksburg and Dutch Gap.

Stems slender; leaves narrowly linear, acute and acuminate, strongly falcate, widest at base, decurrent and adnate, showing a tendency of thenbsp;leaves to crowding and aggregation into groups, in which the members havenbsp;their bases overlapping in some cases, or adnate; midnerve slender butnbsp;distinct.

This plant differs from all the other Sequoias in the peculiar crowding of the leaves at their bases, which seems to arise from a grouping in whorls,nbsp;tlie groups being separated by a comparatively considerable interval.

Heer' describes 8. gracilis as Sequoia^ with alternate branches, approximate ; leaves scale-shaped, imbricated, subfalcate, decurrent at base, and without a midnerve.

This description and the figures given in PI. XXH, Figs. 1-10, PI. XVIII, Fig 1��, agree closely with some of the Potomac plants.

The specimens are found in small bits and fragments of twigs, and these are among the most abundant fossils at the first-named locality.nbsp;Such bits as those given in Fig. 3 are the most common.

Principal twigs slender, penultimate and ultimate ones all in one plane, minute, short, closely placed, alternate and pinnate in arrangement;nbsp;leaves very small, narrowly linear, acute or acuminate, widest at base, decurrent, and mostly crowded ; midnerve slender but distinct.

This plant is a good deal like 8. subulata, but the leaves are proportionally wider and not so falcate, while the ultimate branches are placed at more uniform intervals.

Stem with very broad elliptical to nearly circular leaf-scars, which are spirally arranged.

Leafy twigs unknown ; cones rather large; scales deciduous with age, large, wedge-shaped at base, with the free summits shield-shaped, and furnished with an umbo; upper portions marked with several furrows, whichnbsp;run longitudinally on the sc^le and resemble those of the scales of Ghjp-tostrobus.

These scales, found mostly at the 72d mile-post, are not uncommon there. They have a marked character, which makes it easy to recognizenbsp;them. They are always found in a fragmentary state, only a few scalesnbsp;adhering to the ,axis and widely diverging, indicating that the scales werenbsp;quite deciduous and diverged widely on the ripening of the cones. Anbsp;marked feature is the occurrence of deep furrows on the upper expandednbsp;ends of the scales, which possibly indicates some affinity with Ghjptostrobtis.nbsp;The shape, too, of the scales resembles that of Sphenolepidium, so that thenbsp;type may be a comprehensive one. Plate CXVI, Fig. 7, from Fredericksburg, shows a portion of a cone compressed logitudinally.

Leafy stems unknown; cones large; scales wedge-shaped at base and expanded towards the free ends, surface of the free ends of the scalesnbsp;not made out; the upper expanded portions of the scales are marked withnbsp;' longitudinal furrows as in the preceding species, and the scales appear tonbsp;have been deciduous.

Only one cone of this kind was found. It shows the same longitudinal plications or furrows on the upper portions of the scales as the preceding species, but not to such a marked extent, and the cone is considerably larger than any of those found at the 72d mile-post. It evidently forms anbsp;distinct species.

Leaves sometimes thickened or coriaceous, four-sided, falcate, incurved, keeled on the back and sometimes flattened, possessing several nerves,nbsp;acute at the apex or mucronate, inserted by a narrowed and twisted basenbsp;and decurrent, spirally inserted, or generally distichous on the lateralnbsp;branches and branchlets.

The above description by Saporta^ gives the character of the two types of the leaves of Araucaria. The kind of leaves given in the latternbsp;part of the description is that of certain forms found in the Potomac flora,nbsp;and I have placed these provisionally in this genus.

Stems comparatively stout; leaves small, oblong, elliptical, subacute, narrowed to the base and apex, alternate, distichous, inserted by shortnbsp;slightly twisted footstalks spirally on the stems, placed near the marginsnbsp;and arranged in two rows in the same plane by the twisting of the footstalks; nerves slender, indistinct, several in number, diverging at theirnbsp;entrance into the leaf, then parallel to the summit, where they were notnbsp;distinctly seen.

This plant has the appearance oi Podommites, but the leaves are spi rally arranged, and the nerves are not converging apparently at the summit. It is also like Nageiopsis, but the insertion of the leaves is different.nbsp;It is very much like Gardner�s Podocarpus incerta, from the Eocene ofnbsp;Bournemouth.^

Leaves spirally disposed, arranged in four (?) rows, flat, obtuse, widest near the base, falcately curved upwards, decurrent and imbricated at base;nbsp;nerves thin, parallel, several in number.

'Pal. Frangaise, V�g�taiix, vol. 3, 1878, pp. 412, 413. �Brit. Eocene Flora, vol. 2, PI. XI, Figs. 1-3.

This peculiar plant differs from most Araucarias in several features. On the upper face of the stems scars appear, as if formed by the removalnbsp;of leaves, indicating that they were arranged in four rows. It is possiblenbsp;that the leaves on the upper and lower faces of the twigs were differentnbsp;from the lateral ones and smaller. The top of the twig shows what seemsnbsp;to be a growing bud of undeveloped leaves, and it indicates that the leavesnbsp;were really spirally arranged, but by twisting of the bases or footstalksnbsp;were brought into the same plane, grouping themselves in four rows. Thenbsp;nerves were obscure.

Leafy ultimate twigs terminating with a leaflet like those lower on the twig; stem slender; leaves closely placed, alternate, pinnately arranged innbsp;the same plane, flat, thin, slightly falcate, widest near the base and narrowing gradually to the tips, which are acute, attached by a slightlynbsp;twisted base; nerves several, parallel, and ending as in Zamia, partly onnbsp;the margins near the tips, quite slender and inconspicuous.

The fossils of the Potomac flora belonging to Taxodiuni are found in the group of plants united by Endlicher in the genus Ghjptostrohus, whichnbsp;genus is now by Bentham and Hooker placed with Taxodium. Schenk^nbsp;says of Glyptostrobus, that the leaves are attached spirally and are ofnbsp;various shapes; �they are either upright, short, appressed, oval, acute,nbsp;scale-shaped, the tips on the older stems not seldom divergent, or else onnbsp;the horizontal twigs arranged distichously, linear acute. On upright stemsnbsp;these also are directed upwards. Both kinds of leaves have decurrentnbsp;bases. * * * Ripened cones, woody, oboval in shape, with scales wedge-

shaped and widened at the tips, which are imbricated, and have on their ends a rounded rim marked with from three to seven furrows.�

This description agrees well with the appearance of a number of leafy twigs found in the Potomac strata.

Plate cxxril, Riga. 2, 3; Plate CXXIV, Fig. 2; Plate CXXVII, Fig. 1; Plate CXXXII, Fig. 1; Plate

Stems profusely branching at short intervals; brandies short and rigid, often showing a tendency to a fastigiate arrrangement; leaves on thenbsp;older twigs proportionally long, narrowly elliptical, mostly appressed,nbsp;especially on the upper and lower faces of the twigs, the lateral ones sometimes slightly divergent at the tips and incurved; the leaves on the youngernbsp;stems short, narrowly elliptical, thick, and close appressed, strongly convex,nbsp;and keeled on the back; male aments on the tips of short branches notnbsp;seen; nerves single and thread-like.

This plant is one of the most common conifers at the 72d mile-post. The ultimate twigs often show at their tips a whorl of short, scale-like,nbsp;divergent leaves, that seem to have surrounded the base of the male aments.nbsp;These in all cases had fallen off, and hence their character could not benbsp;made out. There is little doubt, however, that some of the numerousnbsp;aments of conifers from this locality, described as aments of conifers (a),nbsp;(b), (c), (d), come from this plant. Some of the forms of this plant arenbsp;a good deal like Widdringtonia EeicMi, as figured by Velenovsky,�^ andnbsp;they also resemble the branches of Taxodium {Glyptostrobus) expansum^ butnbsp;differs from both of these in the strong convexity of the leaves on. thenbsp;young twigs and their short, elliptical shape, as well as in being morenbsp;rigid, stouter, and much shorter in the twigs. The chief resemblance isnbsp;in the nerves, which in both Widdringtonia and in the Potomac plantnbsp;are single in each leaf, slender and thread-like, running along the middle of the leaves throughout their whole length. The ultimate twigs ofnbsp;the I�otomac plant are sometimes more delicate than in any of the forms

figured, but are short and rigid. Some of the ultimate twigs, as those marked 3� and 3'�, on PL CXXIII, are so short and minute that a good lensnbsp;is needed to make out their details, hut the leaves are seen to he sharplynbsp;defined and very convex. PI. OXXIII, Fig. 3, shows a much-hranchednbsp;twig with very minute and short ultimate branches. PI. CXXII, Fig. 1,nbsp;shows a tendency to fastigiate grouping of the branches.

Branches slender, going off at an acute angle; leaves very small, with the average dimensions, by d�quot;*, narrowly oblong in shape, narrowednbsp;to the base and summit, acute, remotely placed; nerves not seen, butnbsp;apparently single.

This plant is nearest to Glyptostrohiis Groenlandicm Heer, among described fossils, but the leaves are much smaller. It is also somewhat like Sequoia fastigiata Heer, but the twigs are not fastigiate. The leaves seem tonbsp;have been somewhat deciduous, and to have had a mucronate tip.

Twigs alternate and pinnately arranged, going off at an angle of 45�, spreading widely, directed slightly upwards, very long and cylindrical innbsp;form; leaves thick and convex, narrowly elliptical or narrowly oblong,nbsp;proportionally very long and narrow, decurrent, usually close appressed,nbsp;the lateral ones with their tips sometimes diverging ; nerves not seen.

This plant is not uncommon at the locality near Telegrapli Station, and is one of tlie most abundant conifers at that place. To judge from tlienbsp;specimen figured, the plant must have been wide-spreading, for this is anbsp;mere fragment of what must have been a large branch, the basal portionnbsp;of the ultimate twigs being all that is preserved. The rigid character ofnbsp;the species is well shown in this specimen. The specimen figured is one ofnbsp;those with the stoutest ultimate twigs. Many are more delicate and thread-

like. The plant is a good deal like Velenovsky�s Sequoia heteropJiylla, in those forms with the shortest and most appressed leaves (see Die Gymno-sperm. der h�hmisch. Kreideformation, PI. XIII, Figs G, 8). It is also likenbsp;some of the forms of Cyparissidium Heer, but the leaves are longer andnbsp;narrower than those of this genus.

Stems branching copiously; twigs long, cylindrical, branching at long intervals in a dichotomous manner and very irregularly, the branches assuming a fastigiate grouping; lateral leaves on the older twigs oblong tonbsp;ovate, acute, decurrent, diverging slightly, and incurved; facial leaves closenbsp;ajipressed, elongate-oblong, towards the summit of the stem elliptical tonbsp;ovate-acute; leaves on the younger twigs elongate-oblong to narrowlynbsp;elliptical, close appressed, or with the lateral ones sometimes slightly diverging ; midnerve distinct, but slender and thread-like.

This plant is rare at the 72d mile-post, but is one of the most common conifers at the Potomac Run locality. The specimen figured in PI. CXXV,nbsp;Fig. 1, must have been originally very large, for tlie lower and detachednbsp;branch is plainly a part of the upper portion. This plant is, in the form ofnbsp;the leaves, like Glyptostrobus Europceus, and may possibly be an ancestralnbsp;form of this species. The leaves and twigs remind one of Biota pendulanbsp;Endlicher, one of the varieties of 2?. ori�ntalis.

Branches comparatively stout and rigid, rather copiously pinnately and alternately subdivided; leaves thick, convex, very elongate-oblong tonbsp;elongate and narrowly elliptical, close appressed, with ends lancet-shapednbsp;and prolonged into an acute spinous tip, midnerve strong and prominent.

Only one specimen was found, but as the material accessible was very limited in amount and unfavorable for the preservation of specimens, no

idea can be gotten from the apparent rarity of the forms found here of their real abundance. Bioonites BucManus, in great abundance, formednbsp;nearly all the specimens obtained here.

Plate CXXII, Fig. 1; Plate CXXIV, Figs. 3-9; Plate CXXXI, Fig. 5; Plate CLXV, Figs. 1-3;

The principal stems seen are moderately stout and very rigid, the secondary ones mostly slender and rigid, the ultimate ones usually very long, slender, and unbranched, wide-spreading, often very delicate and thread-like,nbsp;going ofF at an angle of about 45�, but from distortion due to pressure frequently appearing fastigiate and irregularly grouped; leaves on the oldestnbsp;stems elongate-linear, acute, close appressed, on the younger stems allnbsp;very narrowly oblong, or narrowly elliptical, acute to obtuse, very closelynbsp;appressed, not distinctly visible without the help of a lens in many cases,nbsp;all spirally arranged; the facial leaves usually acute, the lateral ones usuallynbsp;more obtuse and sometimes slightly divergent at the tips and incurved;nbsp;midnerves slender and thread-like.

This beautiful plant is found in abundance in an interrupted and thin layer of fine clay along with the best preserved of the Angiosperms whichnbsp;occur at the 72d mile-post, such as Menispermites, Sassafras, etc. Strangenbsp;to say, it is not found at the bank on the railroad near by. It evidentlynbsp;had twigs that spread widely in one plane, and some of the twigs indicatednbsp;an expanse of more than a foot. The shale or clay was very unfavorablenbsp;for the extrication of the specimens, and many of them were much brokennbsp;up in taking them out.

This was the case with all of the largest imprints. Plate CXXII, Fig. 1, gives a form with the ultimate twigs of the maximum thickness..nbsp;It gives well the original mode of attachment and the expansion of thenbsp;branches. In most cases distortion from pressure has crowded the twigsnbsp;together and much disguised their true arrangement. This may be seennbsp;in PI. CLXV, Figs. 2, 3, and these figures show also the minuteness ofnbsp;some of the ultimate twigs. They often look like slender threads, the

facial leaves are often much elongated, the sides forming parallel lines and the top being an acute triangle. This elongation of the leaves on thenbsp;front aspect, and the presence of the thread-like midnerves, make some ofnbsp;the twigs to appear striated. The male inflorescence shown in PL CLXVI,nbsp;Fig. 7, occurs at the locality near Brooke, associated with T. Brookense innbsp;such a way as to make it probable that it belongs to this plant.

The varying forms of the leaves on the younger twigs and the character of the midnerves are well shown in PI. CXXTI, Figs. P, P. Tlie leaves on the upper face of the older twigs are not usually preserved, beingnbsp;perhaps sooner destroyed on account of their greater exposure. The lateral leaves are usually so closely appressed that in most cases, if seen without the help of a lens, they seem to be consolidated with the stem, and thenbsp;ultimate twigs look like cords. On many of the ultimate twigs the lateralnbsp;leaves arch slightly away from the stems in the center, the tips curving innbsp;and being closely united to it. The lateral leaves are most commonlynbsp;rather obtusely rounded at the tips. The facial ones, when much drawnnbsp;out, often end in a lancet-shaped point. The thread-like nerves runnbsp;throughout the entire length of the leaves without change in their thickness, and this gives them their peculiar cord-like character, which can benbsp;seen only with the help of a lens.

Most of the plant-bearing material at the 72d mile-post is a confused mixture of sand and clay, composed of torn up and redeposited matter.nbsp;In this occur the various forms of Sphenolepidium found at this localitynbsp;and some of the Angiosperms, but these plants are always in small fragments. No specimens of Taxodium Brookense occur in this material, butnbsp;they are found in the layer of clay above mentioned. As all the well-preserved and most remarkable Angiosperms of this locality occur in thisnbsp;layer, and a number of them nowhere else, it is proper to describe it morenbsp;particularly. This clay layer does not seem to be a deposit of an age different from that of the confused matter, but it is simply a more uniformnbsp;material, the result perhaps of pauses in the movement of the agitatednbsp;waters in which fine clay in small irregular patches was somewhat uniformly laid down. It is only one or two inches thick, and does not continue unbroken, but is cut out here and there by the confused material, and

runs with an undulating dip beneath the railroad track, exposing some five or six feet of length. Tlie claj^ is very fine, unmixed with sand, and fairlynbsp;Avell laminated. In this the leaf imprints occur beautifully preserved.nbsp;Unfortunately but a few feet in length of this substance was found.

Taxodium Brookense is in many features a good deal like the plant which Velenovsky calls Widdringtonia^ BeicMi, and of which he givesnbsp;figures representing an enlarged twig closely resembling some of the formsnbsp;of the Potomac fossil, especially in the shape of the leaves and in thenbsp;lancet-shaped tips of the facial ones. His description in many points willnbsp;apply to the Potomac plant. The older stems, such as the one given innbsp;PI. VIII, Fig. 6, depart more widely from the Potomac forms.

On the whole the twigs of the Potomac plant are stouter and more rigid than those of W. Beichii. Possibly the Potomac fossil is an ancestralnbsp;form of the Bohemian plant. Heer describes a fossil from the Atane bedsnbsp;of Greenland similar to the Bohemian fossil, but says its leaves have nonbsp;midrib. As stated, it is not easy in all cases in T. Brookense to detect thenbsp;midnerve, and Heer may have had specimens in which it was not preserved, although originally present. Velenovsky does not show that tlienbsp;Widdringtonia like cone which he assigns to his plant is certainly connected with it. The shape and the arrangement of the leaves of T.nbsp;Brookense are strikingly like what may be seen in the young leaves ofnbsp;Glyptostrohus pendulus Endlicher.

Copiously branched, with very slender twigs; leaves very narrow, linear, closely appressed, obtuse to subacute; ultimate twigs cord-like,nbsp;and going off irregularly from the penultimate ones; nerves very slendernbsp;and thread-like.

This plant in essentials is the same as the normal T. Brookense, but it is uniformly more slender, the leaves are narrower and always closenbsp;appressed, and it has a more irregular mode of branching, with more

� Die Gymnospermen der bohmisch. Kreideformation, PI. VIII, Figs. 4-6, 16; PL X, Figs. 1, 11, 12; PI. VIII, Fig. 16.

crowded twigs. It is much the most common conifer at White House, where it seems to have been abundant. Owing, however, to the friablenbsp;nature of the clay which contains the imprints and its admixture with sandnbsp;the specimens are poorly preserved. The specimen figured was evidentlynbsp;a very large form originally. When found it extended over five or sixnbsp;inches of area, hut was broken in taking it up.

Branches and twigs alternate, with spirally placed, short, imbricated leaves that are decurrent at base, acute or acuminate on the youngernbsp;twigs, appressed on the older ones, divergent and somewhat curved inwards ; cones placed on axillary lateral branchlets which have closenbsp;appressed leaves and form a raceme, persistent, rounded, or oblong; scalesnbsp;of the cones persistent, leathery, wedge-shaped, with the upper marginnbsp;truncate, when mature, divergent.

This description of the genus by Schenk applies very nearly to a number of coniferous plants from the Potomac flora, which, with the speciesnbsp;of Taxodium, form very important elements in this flora. These two generanbsp;usually are to be found associated together at the same localities and innbsp;the same layers, and with them we usually find some of the species ofnbsp;Sequoia. The constant association of the forms of these three genera is nonbsp;doubt due to the accidents of preservation, the conditions favoring thenbsp;preservation of one promoting likewise that of the others. It is possiblenbsp;that some of these plants may really belong to that group of Sequoias thatnbsp;possesses imbricated scale-shaped leaves, such as S. concinna, etc. In thenbsp;absence of fructification the question can not be positively decided. Certainly these plants possess in the forms of the leaves and twigs manynbsp;features seen in that section of the Sequoias.

Branches long and slender, dividing at long intervals in a dichotomous manner, giving a few rather stout, long, cylindrical branches, showing a

tendency to fastigiate grouping; lateral leaves short, acute, with a distinct MON XV�17

slendei� midnerve, subfalcate, narrowly oblong to narrowly elliptical, decurrent, with the tips slightly divergent and incurved, those on thenbsp;upper and lower surfaces of the stems (facial ones) close appressed, withnbsp;no visible midrib, oblong to elliptical, obtuse to subacute, remote.

This plant is not very rare at Fredericksburg, and is very common at the 72d mile-post, where it occurs in numerous fragments in the confusedlynbsp;mixed sand and clay. The peculiar mode of branching reminds one ofnbsp;Heer�s Sequoia concinna from the Atane beds of Greenland, but the leaves,nbsp;althougdi of the same general character as those of S. concinna, are morenbsp;closely placed and not so long and slender.

Plate CXXVII, Figs. 3,4; Plate CXXVIII, Figs. 2-6; Plate CXXIX,Fig.5; Plate CXXX, Pigs. 4-6,10

Stems branching freely, with long, slender, rigid, alternate twigs, that are obliquely attached; leaves ovate, oblong, or elliptical, thick, short,nbsp;acutely dentate in form, obliquely placed, decurrent, and united at base innbsp;the same plane, with no leaves apparently on the upper and lower faces ofnbsp;the twigs ; midnerve distinct and often strong.

This plant is one of the most common conifers at Fredericksburg. It is much like Sequoia Couttsioe, but the thick, short, tooth-shaped leavesnbsp;differ from those of this Sequoia. PI. CXXX, Fig. 6, and PI. CXXVII,nbsp;Fig. 4, give two twigs which show on their tips two lateral undevelopednbsp;leaf-buds and a terminal partially developed one. The ultimate twigs onnbsp;most of the specimens are placed rather remotely and irregularly, showingnbsp;a tendency to a fastigiate grouping, but in PI. CXXVIII, Fig 5, they arenbsp;closely placed at regular intervals and in a pinnate manner. The plantnbsp;reminds one of some forms of Sphenopteris Mantelli.

Branches and branchlets slender and very long, ultimate branches inserted very obliquely and at irregular intervals, strongly turned upwards;

leaves, so far as seen, inserted only laterally, strongly decurrent, and adnate or united, thick and leathery, strongly recurved, oblong to ovate,nbsp;acute or acuminate, much wider at base than elsewhere, cut away on thenbsp;upper side; midnerve very strong and rigid.

Localities: Fishing hut above Dutch Gap Canal; hill-side near Potomac Run; near Telegraph Station; rare at each locality.

This well-marked plant is in some respects like some of the species of Pagiophyllum (Pachyphyllum). The shape and the great thickness ofnbsp;the leaves are the main points of resemblance. The fine specimen givennbsp;in PI. CXXVII, Fig. 2, shows towards the tips of the ultimate twigs anbsp;recurvation stronger than usual, so that the leaves stand nearly at rightnbsp;angles to the stem. The plant belongs to the type of Sequoia Couttsice.

Branches long, rigid, and slender, sending off at irregular intervals alternate subordinate twigs; leaves, so far as seen, strictly distichous, withnbsp;no facial ones, crowded, adnate at base or overlapping, much wider atnbsp;base than elsewhere, gradually tapering to an acute tip so as to give themnbsp;a triangular or ovate form ; acute or acuminate, straight or slightly falcate,nbsp;attached nearly at right angles to the stems, very thick and dense innbsp;texture, with an unusually large midnerve.

This strongly marked plant is very rare. It is very much like Fagio-pliyllmn Heer {Pachyphyllum Saporta), in the great thickness of the leaves. It is almost exactly like the form of Sequoia Poeichenbachi given by Schenk.^

Branches comparatively stout, alternate; facial leaves elliptical and close appressed, lateral ones ovate, acute, slightly divergent and incurvednbsp;at the tips, strongly decurrent, all with distinct midnerves, on the youngestnbsp;twigs they are elliptical and closely appressed; female strobile terminal on

stout short twigs, oblong in form, with woody or leathery scales wedge-shaped and truncate on the free surface, strongly divergent when mature; malenbsp;aments ? narrowly oblong-elongate, persistent, composed of thin, ovate,nbsp;imbricated scales, terminal at the ends of short slender lateral twigs.

This plant is rather common at the above-named locality. In the character of the cones it is somewhat like Athrotaxopsis, but unlike thatnbsp;genus the scales opened widely on ripening. The leaves also are unlikenbsp;those of Athrotaxopsis. The male aments given at (ci) seem to be pei�sist-ent, for they remain on branches that show the ripened cones. Theynbsp;show open chaffy scales. The plant is not uncommon at the 72d milepost, but very rarely shows cones, and is a good deal like Sphenolepidiumnbsp;Kurrianum Heer {Sphenolepis Kurriana Schenk), but the cones are notnbsp;globose.

Plate CXXVI, Figs. 1, 5, 6; Plate CXXVIII, Pigs. I, 7; Plate CXXIX, Figs. 1, 4, 6, 8; Plate CXXX, Pig. 11; Plate CXXXI, Fig. 4; Plate CLXVII, Fig. 2.

Twigs branching copiously, often much crowded, ultimate twigs rather short and rigid, going off very obliquely and tending to assume a fastigiatenbsp;grouping; leaves imbricated, scale-shaped, the facial ones close appressed,nbsp;elliptical or oblong, subacute, lateral ones oblong or ovate-acute, oftennbsp;with the tips spreading and incurved, decurrent, lateral and facial, leavesnbsp;keeled on the back, all usually thick and sometimes deciduous ; cones notnbsp;seen.

Localities: All the Dutch Gap localities, especially at the entrance to Trent�s Reach and the fishing hut above the canal; Fredericksburg;nbsp;72d mile-post; bank near Brooke; near Telegraph Station.

It is more common at the 72d mile-post than at any other place. It is very abundant here in the form of small fragments. Some of the specimens show a very copious branching and crowding of the twigs, coveringnbsp;the shale with an intricate mass of them. Of such a character is the specimen PI. CXXVIII, Fig. 1 from near Telegraph Station, and PI. CXXVI,nbsp;Fig. 1 from the 72d mile-post. This latter is a form with leaves thinnernbsp;and more slender than usual. In some of the other specimens, such as PI.

GXXVI, Fig. 6, PI. GXXVIII, Fig. 1, and PI. GLXVII, Fig. 2, the leaves are shorter, more convex, and more closely appressed than in others.nbsp;Indeed, there is a considerable degree of variation in the leaves. In suchnbsp;forms as PL GLXVII, Fig. 2, the leaves are thick, horny, and exceedinglynbsp;durable. They can be detached from the shale in the form of small blacknbsp;shining scales.

In this and other forms of Sphenolepidium the facial leaves often appear of somewhat different shape from the lateral ones, being more obtuse, probably from their close appression to the stem. The forms, such as PI.nbsp;GXXVIII, Fig. 1, resemble Ettingshausen�s Widdringtonites Haidingerinbsp;from the Wealden of Hanover (see Beitriige zur Flor. der Wealdenperiode,nbsp;PI. XI, Fig. 1).

This plant is the most common conifer at the 72d mile-post, a place where conifers form the predominant fossils. It is a widely diffused species.

Branches slender, long, remote, going off very obliquely; leaves linear, falcate, acute to acuminate, sometimes acicular, patent, decurrent, muchnbsp;wider at base, with slender but distinct midnerve, apparently distichous,nbsp;and attached only laterally; cones not seen.

This, the normal form of S. Sternbergianum, is comparatively rare, being much less common than the variety densifoliuni. It differs fromnbsp;Heer�s forms only in not showing leaves on the upper surfaces of the twigs,nbsp;but this is no doubt due to the removal of these leaves from their morenbsp;exposed position.

Plate CXVIII, Fig. 7; Plate CXXI, Figs. 5, 7, 9; Plate CXXV, Pig. 2; Plate CXXIX, Fig. 3;

Branches slender, ultimate twigs going off very obliquely so as to appear dichotomous, tending to a fastigiate arrangement, subdividing irregularly ; leaves short, lateral ones acute, linear to narrowly ovate, diverg-

ing, falcate or subfalcate, comparatively closely placed, strongly decurrent ; midnerve distinct; facial leaves ovate to elliptical, apparently obtuse and smaller than the lateral ones, closely appressed, with often no midnervenbsp;visible, sometimes removed by maceration; cones not seen.

Localities: Near Telegraph Station; hill-side near Potomac Pun; 72d mile-post; Fredericksburg.

This plant is rare at all the localities except the 72d mile-post, where it is quite common. Plate CXXXI, Fig. 1, shows a number of undeveloped branches and buds, This plant is a good deal like Sequoia fastigiata.nbsp;It has the leaves more crowded, straighter, and less diverging than the normal 8. Sternbergimum, and tlie facial leaves, probably owing to compression, seem to be blunt and elliptical in form.

OYMNOSPERMOUS FRUITS.

The following fruits of Gymnosperms, not being connected with leafy twigs, probably in some cases belong to plants described from their leafnbsp;branches under other names. In some cases, owing to their imperfectnbsp;preservation, it is not possible to place them with certainty in their truenbsp;position.

Under this head I group certain cones that have in the main the character of some forms of Abies.

This cone, although very impei'fect and wanting the base and the apex, was evidently very long. Only the bases of the scales are preserved,nbsp;and those on the upper face have been stripped off. It seems to be morenbsp;like that of Abies than that of any other conifer. It resembles Gunning-hamites Oxycedrus Ettingshausen, from the Cretaceous flora of Nieder-scbona.

Cones of medium size, elliptical in outline; scales thin, long, imbricated, and closely appressed; axis thick.

This cone is not uncommon at Fredericksburg. It is very much like that of Abies. In PI. CXXXII, Fig. 9, the upper surface of the cone hasnbsp;been accidentally removed so as to expose the axis. This, towards its base,nbsp;is very thick. The species seems to be of the same general character as A.nbsp;macrocarpus, but the cones are smaller and much shorter.

Cone oblong, very narrow in proportion to its length ; axis projior-tionally very thick and short; scales short, comparatively thick at base, thin tovFards the summit, imbricated, closely appressed.

This was found in only one specimen, which, although imperfectly preserved, is clearly different from the two previously described species.nbsp;It was evidently very narrow in proportion to its length, for the base andnbsp;summit are. not preserved. The scales appear unusually thick at base as ifnbsp;still inclosing the seed, and they are proportionally very short. They havenbsp;been removed from the upper surface of the axis so as to show the scarsnbsp;of insertion.

Under this head I place certain fragments of cones that appear to be more nearly allied to Araucaria than any other conifer, but whose truenbsp;place is doubtful.

Cone obovate, rounded at the summit; scales large, numerous, thick, transversely subrhomboidal to nearly round, shield-shaped, umbonate.

Only one specimen was found. The cone, whose form is pretty well preserved, is in shape and in the character of the scales a good deal likenbsp;Sequoia. It resembles more than any other cone that of Araucaria Cretaceanbsp;Brongniart, as given by Schimper,^ but it is much smaller.

Scales of the cones varying considerably in size and shape, attaining the maximum dimensions in length of �� and in width across the top ofnbsp;3*quot;�, with the minimum of 3.5'quot;� by 1.5�; scales probably closely appressednbsp;and imbricated, wedge-shaped, and narrowed at base into a sort of footstalk, thickened at the summit, and rounded on the upper margin, with anbsp;depressed transverse furrow, very deciduous, and always found scatterednbsp;singly and sparingly in the clay.

These scales are not uncommon. No cone was found from which they could come. In their shape and deciduous character they resemble somenbsp;of the forms of Abies. The scales are like those of Bammara also. Nearnbsp;their summits they all show on one face a distinct curving imprint, as ifnbsp;made by the pressure of the terminal edges of the overlapping next lowernbsp;scales. I have taken its specific name from Aquia Creek, near whichnbsp;the locality yielding them occurs.

Under the head of Carpolithus I place a number of nut-like seed of conifers which have not been found in connection with leafy branches,nbsp;and whose proper place can not be made out with any certainty. Nonbsp;doubt some of them belong to some of the conifers described with othernbsp;names, the characters being taken from leafy branches. These fruits formnbsp;an important element in the Potomac flora, and they are the most abundant gymnospermous fruits found.

Seed nut-like, with a hard smooth surface, broadly elliptical in shape, sessile, on a shoi't stout stem, crowded into a fascicle, comparatively large.

Only one specimen was found. As this fruit has not been found attached to any leafy twigs, its place can not be fixed. It occurs at Fredericksburg with numerous leafy twigs of Gephalotaxopsis, and as the fruitnbsp;of Cephalotaxus has a nut-like bony seed, it is probable that these fossilsnbsp;belong to some species of the first-named genus. The twig to which thenbsp;nut-like seeds are still attached is more like the twigs of Gephalotaxopsisnbsp;than any of the other coniferous wood found at the locality.

This fruit and those next to be described have suffered a good deal from maceration; hence, as now presented, they must be more or lessnbsp;disguised.

Seeds oblong, obtuse, smooth, grouped in tln-ees, the individuals more or less united and sessile, attached to the sides and summits of short stoutnbsp;stems, which are attached to thick, woody, principal branches: texture ofnbsp;the nut like seed hard and woody.

This is the most abundant Carpolithus at Fredericksburg. The seeds have a peculiar character of union at the bases, forming a palmatelynbsp;three-lobed cluster. Possibly this union, real or apparent, may be due tonbsp;the immaturity of the seed if it is real, for they show gradations in separation which seem to be connected with age, the oldest and largest beingnbsp;most distinct. Thus in Fig. 6 the lowest group on the right-hand sidenbsp;shows seed separated nearly to the base, wliile in some groups, as in thenbsp;upper part of Fig. 4, the individuals are united nearly to their summits.nbsp;These seed also are probably those of Gephalotaxopsis. They remind onenbsp;of Lesquereux�s Equisetum globulosum. (See Cretaceous and Tertiarynbsp;Floras, PI. XLVIII, Fig. 3.)

Seeds hard, smooth, and nut-like, small, obovate or broadly elliptical, sometimes g-lobular, often more or less strongly ridged, ridges seen for thenbsp;most part three in number, borne singly on short pedicels, arrangednbsp;alternately on the principal branches, and tending to assume a fasciculatenbsp;grouping.

These fruits are rare at the first-named locality, but are not uncommon at Dutch Gap. The ridges seen do not seem to show themselves unlessnbsp;maceration has removed some of the exterior tissue of the seed. The seednbsp;seem originally to have had smooth, firm exteriors. Like the precedingnbsp;species of Carpolithus, they were probably inclosed in some sort of fleshynbsp;matter, possibly having been plum-like. These seeds occur with abundantnbsp;impressions of the leaves of Baieropsis, and the pedicels with the principalnbsp;stems resemble the woody matter of Baieropsis more than that of anynbsp;other plant. It is probable that these are the seeds of some species of thatnbsp;genus, perhaps of B. pluripartita, the one with which they are most commonly associated. The fact that almost exactly similar seed are foundnbsp;constantly with Baiera M�nsteriana makes this all the more probable, sincenbsp;that plant seems to be nearer to Baieropsis than to the true Baieras. Thesenbsp;latter, according to the figures of Heer and Nathorst, have their leavesnbsp;sparingly subdivided into lobes of equal importance, are very narrowlynbsp;wedge-shaped, and are grouped on the summits of short shoots. Thesenbsp;features are not found in some of the forms of Baiera M�nsteriana. Thesenbsp;seed resemble Lesquereux�s Cinchonidium ovale, but these latter ai-e smaller.nbsp;They may be compared also with the seed of Heer�s^ Czekanowskia. Theynbsp;are strikingly like Lesquereux�s Carpites gemmaceus? PI. CLXVIII, Fig. 7.nbsp;is peculiar in showing only one strong rib, instead of three.

Seed small, globular in form, smooth, nut-like, crowded together closely into a species of head, which is sessile, or borne on very shortnbsp;pedicels, and carried on short lateral branches.

These seeds are very rare. They probably belong to some species of Baieropsis^ and, as the most abundant and indeed almost the only speciesnbsp;of this genus occurring at that place is B. expansa, these seed may belongnbsp;to it. They are a good deal smaller than those of the preceding species.nbsp;Owing to the close crowding and the very short pedicels, some of thesenbsp;forms appear united at base, as in C. ternatus.

Fruit apparently composed of a whorl made of three pairs of nutlike seeds united near their bases and of a single one radiating from a central point, probably the summit of a pedicel; the component nut-likenbsp;seed are obovate, obtuse, and rounded at the free ends, narrowed to anbsp;sort of neck at the place of union, marked by transverse stria3 or wrinkles,nbsp;which run around the bodies.

Only one specimen was found. As it is quite possible that this is distorted by pressure, it may be much disguised, at least in the grouping of the seed-like bodies. I am unable to offer even a conjecture as to the truenbsp;place of this group of bodies.

Seed of medium size, elliptical or obovate, smooth, nut-like, and firm, in pairs at the summit of a very short pedicel, almost sessile.

Only one specimen was found. The left-hand nutlet of the pair has had its summit removed by accident, and hence does not present the true

shape of the seed. It is under these circumstances impossible to say anything positive about the affinity of the fossil. It is, however, in the pairing of the seeds, their shape and position, most like the seeds of Ginkgo.

Seed elliptical, prolonged above into an acute beak of considerable length, which is usually bent to one side, below narrowed into a pedicelnbsp;for attachment to the stem; on the upper surface usually three strongnbsp;ridges shown, which run longitudinally the entire length of the fruit.

This form of seed is not uncommon at the bank near Brooke, where they are never found attached, but occur scattered through the clay. Thenbsp;unusual form shown in PI. CLXVII, Fig. 6, was found in a single specimennbsp;at the fishing hut above Dutch Gap Canal. It shows no ridges, but anbsp;kernel-like nucleus within the mass of the seed. It may be a differentnbsp;species. At the bank near Brooke, where these seed are most common, nonbsp;plant occurs to which these seeds could probably belong besides Baierop-sis foliosa and Nageiopsis angustifolia. The former is quite common, andnbsp;it is probable that the fossil now in question forms the fruit of it.

Saporta^ calls attention to the fact that the seeds of the older conifers are usually angled, and says that the young ovule of Salisburia is slightlynbsp;compressed, showing two or three angles. This two or three sided structure, showing more or less pi'onounced keels or wings, is found, as he says,nbsp;in the most primitive conifers. It may then be questioned whether or notnbsp;the angled or keeled surface of the ovule of Salisburia is an embryonicnbsp;feature. It will be noted also that the young ovule of Salisburia shows anbsp;tendency to form a beak on its free extremity. The possession of a beaknbsp;may also be an embryonic feature. If so, it is interesting to note so manynbsp;embryonic characters in these seeds, which probably belong to Baieropsis,nbsp;an old member of the Salisburia family.

These seed show a considerable amount of variation, and possibly they do not all belong to the same species.

Seed of medium size, broadly pear-shaped, with a very short acute projection or mucro on the summit as wide as long, narrowed below intonbsp;a comparatively very stout pedicel, showing on the upper surface twonbsp;strong flat ribs, which are placed on each side of the medial line and runnbsp;nearly parallel with the margins.

Only one specimen of this plant was found, and hence its character is imperfectly shown. It is clearly different from all the other Potomac formsnbsp;of Carpolithus. It shows a peculiar flaring out in width in the middle.nbsp;It is probably a seed of some Baieropsis.

Seed large, elongate, broader at one end than at the other, curved on one margin and nearly straight on the other, convex, covered with a thick,nbsp;smooth, and shining epidermis.

This curious form casually inspected looks something like the imprint of a shell. It is in shape and size unlike all the forms of Carpolithusnbsp;found in the Potomac beds. It may be a Cycadeospermum.

Seed small, subrhombic to elliptical in form, acute, much narrowed at each end, upper surface marked with three lines denoting ridges, sessile;nbsp;principal stem comparatively stout.

This and the form next to be described are very rare. They are both much like the nut-like seed of Cephalotaxus, and probably belong to somenbsp;species of Cephalotaxopsis.

Seed of medium size, elliptical, widest towards the summit, ending in a short rigid tip (mucro), narrowed gradually towards the base into a verynbsp;short stout pedicel, by which it is attached to the principal stem, markednbsp;on the upper surface with three strong lines or ridges.

In the genus Cycadeospermum I place various smooth horny seeds, which resemble those of cycadaceous plants more than those of conifers,nbsp;but which are always found detached and isolated. This fact, and thenbsp;additional one That they are usually imperfectly preserved, render thenbsp;correct placing of these plants impossible. They are always few in number, and form a very insignificant element in the Potomac flora.

This small seed is very rare. It was found only isolated and not in connection with any leafy twigs. The seed figured by Heer^ as the seednbsp;of Ginkgo sibirica are a good deal like this one.

Seed of medium size, obovate in form, narrowed towards the base, where a trace of the pedicel is seen ; smooth and firm.

This seed is something like Carpolithus Virginiensis, but it is larger, and besides is smooth and glossy on the surface.

Seed of considerable size, smooth and glossy on the surface, spatulate in form, truncate and ahriiptly rounded off at the base, narrowed towardsnbsp;the upper end ; the sides nearly straight.

These seed, found always detached, are covered by a smooth, glossy, parchment-like epidermis, which peels off from the stone. It is the mostnbsp;common seed at the Potomac Run locality, but still is not abundant.

Seed broadly elliptical, nearly orbicular, smooth and firm, covered with a smooth, shining epidermis, that is very durable.

This seed must have had a considerable amount of woody matter in its composition, as it leaves a deep depression in the clay. It is the mostnbsp;common cycad seed at Dutch Gap.

Seed small, suborbiciilar; surface smooth and firm, with a leathery, durable epidermis.

This small seed, found in only one specimen, is in shape similar to the preceding, but is much smaller.

This seed, found in only one specimen, is very long in proportion to its width. It seems to be a distinct species.

This may have been the pollen-bearing catkin of some unknown Angiosperm. As only one specimen was found, and it was very imperfectly preserved, nothing definite can be said as to its true place.

This figure shows two capsules of some fruit apparently united at base and borne on a short pedicel. They are elongate-elliptical in shape,nbsp;having at the summit tooth-like projections, as if due to incipient dehiscence.

This fossil, which appears to be nearer Callitris than any other, seems to be a broadly oblong cone, truncate at the summit. It is attached by anbsp;very stout pedicel to a thick twig, and appears to be split into severalnbsp;portions, which are narrowly oblong.

Locality: It was found in only one specimen, at the fishing hut above Dutch Gap Canal.

The figure represents what seems to be a seed of Pinus. It is of small size, elliptical in form, and has attached to it a large scale.

Fig. 7 gives a number of small capsules, natural size, grouped in a radiate manner, that resemble the pollen sacs of Taxus. They may belongnbsp;to Athrotaxopsis.

Axis stout, with a broad, deep depression at its summit, surrounded by an elevated ridge which has been left by the fruit. Bracts in at least twonbsp;whorls, which alternate with each other, and are situated beneath andnbsp;around the scar left by the detachment of the fruit, oblong to narrowlynbsp;ovate in shape, apparently originally covered with numerous extremely finenbsp;hair-like appendages, which, however, owing to the accidents of preservation, are now often absent.

This fossil is rare at the latter locality, and is not uncommon at the former in the layer with Dioonites BucManus, Frenelopsis parceramosa, etc.nbsp;Some of the bracts are smooth and show no traces of the hair-like appendages. The best preserved specimens, however, show them very distinctlynbsp;under a lens, and to the unaided eye they appear as fine strim. The bractsnbsp;were evidently thick and fleshy, for in many cases they appear convex onnbsp;the surface.

Von Otto�^ gives illustrations of large star-shaped bodies, which he calls Asterosoma radicAforme. These resemble the Potomac fossils now innbsp;question, but they are much larger, and have fewer bracts than W. Vir-giniensis. Von Otto says of these fossils, that in nearly all four specimensnbsp;found there occur near the star-shaped bodies thread-like little cylindersnbsp;which wind about and occasionally lie npon the star-shaped bodies. Thisnbsp;description would seem to indicate the existence on these bodies of threadlike appendages like those on the Potomac fossils. These Williamsonia-like fossils of Von Otto come from the upper Quader of the vicinity ofnbsp;K�nigstein in Saxony.

* Additameute zur Flora des Quadergebirges, pt. 2, PL II, Fig. 4; PL III, Figs. 1, 2. MON XV-18

The plants next following do not possess characters that place them definitely in any particular group of vegetable forms. I give figures ofnbsp;them, as they seem to be worthy of notice, and, so far as can be made out,nbsp;they are different from any of the fossils described under other heads innbsp;this memoir.

At the fishing hut above Dutch Gap Canal we occasionally, but rarely, find, on certain thin layers of fissile, very fine-grained clay, a number of minute circular markings confusedly associated together. As seennbsp;under a lens, -they are in the form of a circular raised ring, in the center ofnbsp;which is a minute knob. They occur also in the red clay ball in the banksnbsp;of Dutch Gap Canal.

This peculiar stem is more like an EpJiedra than any other plant known to me. It has a number of long, slender, woody cylindrical stems,nbsp;which radiate from a common point. In several places they seem to benbsp;jointed, but the jointing does not appear to be generally present. In several there are scars, as if left by the detaching of twigs. The stems arenbsp;decorticated.

This plant is composed of a number of woody cylindrical twigs, that branch in a dichotomous manner, and pursue an irregular, flexuous course.nbsp;In the irregular branching and flexuous character of the twigs it looksnbsp;more like a root than an aerial growth.

This singular fossil comes from Fredericksburg in only one specimen. The main stem seems to have been rather succulent. It has attached laterally towards the top a number of flat leathery appendages that seem tonbsp;liave had a slight woody axis or midnerve. The}quot; remind one of the rib-bon-like subterranean leaves of Stigmaria. The fossil is apparently a root.

This fossil appears in the form of large main stems, that are strongly striated and send off irregularly large striated branches. They seem tonbsp;have been somewhat succulent in character, and probably were roots.

This fossil, found in only one specimen at Fredericksburg, is very imperfect. It shows the curious feature of having a number of stemsnbsp;radiating from the same zone on a common stem. The bases only of thesenbsp;are preserved. They appear swollen and even bulbous, and are markednbsp;by transverse striae. They look somethi ng like the singular stems found atnbsp;Baltimore, and figured on PI. CLIX, Figs. 4, 5.

lilis is a woody branching stem, found in only one specimen at Fredericksburg. It is without significant character, being decorticated. It may belong to Athrotaxopsis.

The specimens of this plant show very long and slender cylindrical stems, with a comparatively small woody axis, surrounded by a succulent

cortical layer. The branches, which are like the main stems, go off at long intervals from the same zone, apparently in whorls. They go off usuallynbsp;at right angles from the main stem and then bend upwards at a riglit angle,nbsp;so as to be parallel to the main stem. The branches are often as thick asnbsp;the main stem.

This fossil is composed of long cylindrical stems, which send off very obliquely, and apparently in whorls, branches which are similar to the principal stems. The stems and branches had a stout woody axis, which wasnbsp;surrounded by a cortical layer, succulent in nature, and of considerablenbsp;thickness. This latter sometimes leaves a wrinkled and puckered marginnbsp;to the woody axis, but it is not always preserved. The bases of thenbsp;branches seem to be swollen, and they are marked by transverse scars,nbsp;which may be due to the fall of bud-scales, or may be simply wrinklesnbsp;from shrinking in the cortical layer. The plant may be the stem of Cepli-alotaxopsis or Baieropsis.

This fossil occurs in the form mostly of detached, circular, sheath-like impressions, having a small circular orifice in the center. The imprintsnbsp;show a number of moderately strong nerves or ribs, that radiate from thenbsp;central orifice and end in spike-like teeth around the margin. Usually anbsp;number of these imprints are found near one another, and sometimes vaguenbsp;indications of a stem occur, but too much disguised by maceration to givenbsp;any idea of the mode of attachment. The imprints look more like sheathsnbsp;of some Equisetum than anything else.

The angiosperms of the Potomac flora form an important element in it. In number of species, however, they are far inferior to the conifersnbsp;and ferns, and do not equal these in the extent of their diffusion. Thenbsp;localities at which angiosperms occur in notable amounts, in the stratanbsp;in place, are the 72d mile-post; bank near Brooke; White House Bluff;nbsp;the two localities at Baltimore and at Fredericksburg. The plants atnbsp;Fredericksburg are much more archaic in type than those of the othernbsp;localities.

It is, then, only from Fredericksburg northwards that we find this modern element playing an important part in the flora of the beds in place. All of the localities in this more northern portion of the Potomac area donbsp;not contain any considerable proportion of these plants. None occur atnbsp;the hill-side near Potomac Run, and only a few fragments are found on thenbsp;road-side near by, as well as near Telegraph Station. The two localitiesnbsp;at Baltimore show the Variegated Clay or upper member of the Potomacnbsp;in place over the plant-bearing beds. At Brooke the Eocene caps the fos-siliferous strata. Only a few imperfect fragments of angiosperms occur innbsp;the strata in place in the immediate vicinity of Dutch Gap Canal; but atnbsp;Deep Bottom, where the Eocene caps the Potomac, angiosperms predominate in the fossils found in the disturbed bowlders of sandy clay and claynbsp;which come from the destruction of beds that once lay upon the sand ofnbsp;the lower Potomac These are of more recent type, as are those of thenbsp;Brooke localities, White House Bluff, and the two Baltimore localities.nbsp;But, as has been stated before, these beds can not be separated in age.nbsp;The Lower Potomac era seems to have had a flora that was rapidly changing. In the lower and middle strata, ferns, cycads, equiseta, and conifers predominated, giving the flora a Jurassic facies, but with these werenbsp;mingled a considerable number of angiosperms, mostly of archaic type.nbsp;The strata of Dutch Gap Canal and at Fredericksburg give us a good typenbsp;of this portion of the formation. Towards the upper part of the formation

angiosperms abounded and predominated, several having living genera, but with them many of the plants found lower down in the formation stillnbsp;existed. The beds at Brooke, White House Bluff, and Baltimore are typesnbsp;of this portion of the formation

It is a noteworthy fact that many of the fossils that are nearly allied to living genera are comprehensive types, showing perhaps ancestral formsnbsp;of living types. The same may be said of the conifers that are associatednbsp;with these angiosperms, and wliich show affinities with living genera of conifers. They are not, then, either the conifers or the associated angiosperms,nbsp;so recent in type as a hasty inspection might indicate. When in anynbsp;series of beds at a given locality the fossils are of the character of thosenbsp;found at Fredericksburg and at Dutch Gap, we may conclude that thenbsp;absence of angiosperms is explainable by the removal by erosion of thenbsp;upper strata, which contain them in large numbers.

Another fact that should be noted as probably indicating the really great antiquity of the most modern-looking angiosperms is the great raritynbsp;of individuals in most of these, and it is the most recent types that shownbsp;the fewest individuals. This probably means that the type is of recentnbsp;introduction. This feature should, however, be accepted with caution as anbsp;basis for reasoning concerning the scarcity or abundance of forms, sincenbsp;we know nothing concerning the conditions which favored or opposed thenbsp;preservation of given plants. Apparent relative abundance or rarity maynbsp;be determined solely by the conditions controlling fossilization. Then, too,nbsp;the amount of material obtained from a given locality has, of course, muchnbsp;influence in fixing the apparent abundance of the plants found only atnbsp;that spot. These remarks apply with special force to the Potomac flora,nbsp;which shows such a remarkable localization of the plants. It will be,nbsp;perhaps, proper to state in this connection that a veiy large amountnbsp;of material was obtained at the entrance to Trent�s Reach; fishing hutnbsp;above Dutch Gap Canal; Fredericksburg; the two Brooke localities; anbsp;smaller amount, but still large, at White House Blutf, the two Balti-nore localities, and the two Potomac Run localities, and very little fromnbsp;the others.

Leaves very thick and leathery, with entire margins, elliptical in snape; nerves three in number, slender but distinct, one medial and twonbsp;marginal, the latter parallel to the margins of the leaf, all running fromnbsp;the base to the apex, and apparently uniting at the apex �, no other nervesnbsp;seen.

Only one specimen was found. Tlie thick leathery texture of the �eaves concealed all the nervation except the three main nerves. Theynbsp;� continue without much diminution from base to apex. 14� is a reproduction of the leaf.

Leaves in outline elliptical or spatulate, in texture quite thick, narrowed gradually below into a long petiole; leaves inserted very obliquely on comparatively stout stems, arranged spirally; petiole, on entering thenbsp;lamina of the leaf, splitting up into a comparatively stout middle nervenbsp;and two lateral ones, the latter varying in stoutness; each main nervenbsp;sends off very obliquely subordinate nerves, which anastomose witli thenbsp;adjacent ones to form long and irregular meshes; ultimate nerves not seen;nbsp;the midnerve splits up towards the apex by sending off lateral nerves.nbsp;These leaves are more like those of some of the acacias of New Hollandnbsp;than any other plants. We may compare tliem with the phyllodes ofnbsp;Acacia salicina Lind., and A. longifolia Willd.

Entire leaves not seen, but long elliptical in form, gradually narrowing below into a long petiole; midnerve persistent to near the summit of thenbsp;leaf, comparatively strong, sending off very obliquely slender secondary

nerves, and these in turn sending oflf subordinate ones which are very slender, and anastomose at very long intervals to form very long and largenbsp;meshes; ultimate nervation not seen.

Localities: Fishing hut above Dutch Gap Canal; red clay ball in the banks of Dutch Cap Canal; very rare.

This leaf differs from the other species of the genus in its large size, in the great proportional size of the midrib, and in the very slender lateralnbsp;nerves which are sent off from the basal portion of the leaf, and for somenbsp;distance diverge very slightly from the midrib. The lateral primarynbsp;nerves hardly surpass in stoutness the secondary one's.

Leaves elliptical or spatulate in shape, mostly of the latter form, inserted spirally and very obliquely on stout stems by means of longnbsp;petioles, into which the leaves gradually narrow, forming wedge-shapednbsp;bases; petiole at the base of the leaf lamina splits up into three nerves otnbsp;nearly equal importance, but with the middle sliglitly predominating; eachnbsp;of these sends off very oblique branches, which are quite slender andnbsp;anastomose at long intervals, forming very long and large irregularlynbsp;shaped meshes; ultimate nervation not seen.

Localities: Fishing hut above Dutch Gap Canal; the red clay ball in the banks of Dutch Gap Canal; rare.

The plant is most common at the first-named locality, but is not abundant anywhere. The leaves of this plant may be compared withnbsp;those of Leucospermum conocarpum R. Brown.

Main stem proportionally very stout; leaves spirally placed and very obliquely on the stems, small, elliptical in sliape, narrowed gradually withnbsp;a wedge-shaped base into a petiole of varying length, subacute, nerves asnbsp;in the preceding species.

Only one specimen was found. On the branch preserved on the left side of the figure only two leaves are to be seen borne on the summit;nbsp;but this is no doubt due to the fact that the lower leaves have been accidentally removed.

Leaves small, variable in shape, ranging from narrowly elliptical to subspatulate and broadly elliptical, often inequilateral, placed spirally andnbsp;very obliquely on the stem, with long petioles; leaf-substance comparatively thick and hiding the nerves; nervation as given in the genericnbsp;description, but not distinct; primary nerves slender; ultimate nerves notnbsp;seen.

I group under this head a number of leaves with a very archaic type of nervation that occur in the Potomac flora. In their nervation, and innbsp;many cases in the form of the leaves, they bear a greater resemblance tonbsp;species of Frotea than any other plants. The main points that characterizenbsp;them are the absence of any pronounced difference in the size of the primary nerves, the great slenderness of these, the lax and irregular reticulationnbsp;formed, and the uniformly strong ultimate nerves, which give a reticulation that reminds one of ferns. Indeed, I was for some time in doubtnbsp;whether some of these leaves were really angiosperms and not ferns.nbsp;There are two types of these leaves, that differ only in the presence or thenbsp;absence of a distinct midrib; when the midrib is present the leaves assumenbsp;an elliptical form; when it is absent, they tend to take an orbicular shape.nbsp;We might perliaps divide the genus into two subgenera according to thisnbsp;distinction, giving one the name rotundatum. and the other the appellationnbsp;elongatum.

The genus may be described as follows: Leaves orbicular or elongate in form; in the case of the former, no midrib present; in the case of thenbsp;latter, a thick, vaguely defined, and apparently somewhat succulent midrib

exists; petioles proportionally very thick and apparently succulent; nervation of the primary order very slender, and with little or no difference in the strength of the primary nerves; reticulation of all orders lax, irregular in shape, and varying in the size of the meshes; ultimate nerves strong,nbsp;all of equal strength and fern-like. These leaves form an important portion of the angiosperms that occur with a predominant flora of Jurassicnbsp;type, as at Fredericksburg, and they give a very ancient look to the angio-spermous element of the flora.

Leaves small, reniform, inequilateral; leaf-substance quite thick ; petiole proportionally very thick and apparently succulent, splitting up on entering the^leaf into a number of neaidy equal primaiy nerves, which,nbsp;repeatedly subdividing in a palmate manner and anastomosing,' fill thenbsp;leaf with a very irregnlar lax reticulation, the branches being nearly ofnbsp;equal strength with the primary nerves ; ultimate reticulation not seen.nbsp;The smallest reticulation seen is formed by comparatively strong branches,nbsp;that generally make large, nearly right angles with their parent nerves.nbsp;The branches of the primary nerves go off very obliquely.

Localities: Fi�edericksburg ; 72d mile-post; fishing hut above Dutch Gap Canal; rare.

The imprint given in PI. CXXXIX, Fig. 3, represents the entire leaf On the right-hand lower side it has been pressed upwards from below so asnbsp;to roll over the lower margin of the leaf upon the nerves, making the outermost of them appear to issue from a marginal nerve. This pressure hasnbsp;probably produced also a distortion of the primary nerves in the left-handnbsp;half of the leaf, crowding them together abnormally. The thick substancenbsp;makes it difficult to follow the iiltimate nervation. Plate CLX, Fig. 1,nbsp;gives a large fragment of a leaf much mutilated and wrinkled tiunsversely.nbsp;This specimen, presenting its lower surface uppermost shows the nervesnbsp;much more distinctly. It shows that the penultimate meshes seen are sub-rhornbic in shape, being made by nerves meeting mostly under acutenbsp;angles, but the ultimate or smallest meshes are irregulai-, subrotund, or

polygonal in form, quite different from those next above them in size. This figure does not show any of the original margin of the leaf or of the petiole, although the outline and dimensions of the leaf are evidently retainednbsp;nearly unchanged.

This curious leaf, in shape and nervation, reminds one of the leaves called ProtorJiipis by vai�ious authors, under the supposition that they arenbsp;the prothalli of ferns. It may well be questioned, however, whether somenbsp;of these are not ancient forms of dicotyledons. The nervation of the Potomac plant is something like that of a fern, and is decidedly archaic in type.nbsp;The form is similar to that of some Hedera, as H. primordialis Saporta, butnbsp;in Hedera the midrib and primary nerves are much stronger than the secondary ones. In the midrib splitting up into numerous primary nerves ofnbsp;nearly equal size, in the dichotomous forking of the latter, and in the verynbsp;thick petiole we have a strong resemblance to some of the Proteaceoe, asnbsp;Protea cordata Thunb. In shape it is a good deal like Begonia liydrocotyli-folia. It is also similar in shape to Populus arctica Heer.^ Tliis speciesnbsp;may be taken as the tyjje of the subgenus Botundatum of the forms of Pro-fecephgllum.

Leaf small, orbicular in sliape, slightly lieart-shaped at base; primary nerves all nearly of equal thickness, diverging slowly, and radiating fromnbsp;the base of the leaf, sending off obliquely very slender branches, whichnbsp;anastomose to form irregular comparatively large meshes; ultimate nervesnbsp;forming oblong pentagonal or hexagonal meshes.

This plant also belongs to the rotundate section of Protemphyllmn. It more than the preceding species resembles Hedera^ but the radiatenbsp;arrangement of the slender primary nerves does not agree with that genus.nbsp;It may also be compared with Protea cordata Thunb. The nervation ofnbsp;this plant is much like that of Banhsites Saportanm, Velenovsky (see Die

Flora der b�hm. Kreideform., PL I, Fig. 18). Conospermites hakeoefolius (Fig. 11 of the same plate) has a nervation similar to that of the Potomacnbsp;plant.

This fossil is too fragmentary to juslify an attempt to determine its species. It forms the upper part of an elliptical leaf, most probably has anbsp;midnerve which towards the sitmmit splits up into branches. These arenbsp;slender and are sent off obliquely ; they subdivide irregularly into secondary branches, which anastomose irregularly to form large lax meshes. Itnbsp;may be compared with Protea glabra Thunb. It belongs to the elongatenbsp;section of Protecepliyllum.

Leaf rather large, spatulate, oblong _ or oblong-elliptical, narrowed very gradually below into the petiole; summit not seen; midnerve stout,nbsp;and continuing to near the tip of the leaf; secondary nerves very slender,nbsp;leaving the midrib at a more or less acute angle, and arching around in annbsp;irregularly flexuotis manner to unite with those of the same order nextnbsp;above, sending off branches obliquely, mainly on the outer side, wliichnbsp;pursire a flexuous course parallel to the margin of tlie leaf, finally dissolving into smaller branches; the lateral nerves anastomose into large,nbsp;irregular meshes, made xxp of subordinate meshes, the minor branches of thenbsp;lateral nerves, which meet under large angles, forming a net-w'ork that isnbsp;very irregular; leaf-substance moderately thick; the ultimate reticulationnbsp;strong and fern-like.

nervation is very lax, irregular, and archaic in type. The leaves are always quite fragmentary, but so many specimens are found giving allnbsp;parts of the leaf, that a quite reliable restoration can be indicated. In PI.nbsp;CXL, Fig. 2, I give a full-size restoration of the leaf of the largest dimen-

sions. The nervation is something like that of Ficus protogoca, Ettings-liausen, from the Cretaceous strata of Niedersch�na.^ The irregularity of the areolation, the slenderness of the primary nerves, and the proportionally very strong ultimate reticulation make the leaf more like some Froteasnbsp;than any other living forms.

Leaves of medium size, ovate-acute, with the tip bent to one side, abruptly rounded at base, and subcordate; midnerve very thick and apparently somewhat succulent; primary nerves very slender, going off nearlynbsp;opposite in pairs, basal pair leaving at a very large angle and curvingnbsp;strongly around approximately parallel to margin, those higher up leavingnbsp;at more and more acute angles, curving gently until neai- the margin of thenbsp;leaf, and then bending strongly upwards, gradually approaching the margin, sending ofiP slender branches, which anastomose to form large, lax, andnbsp;mostly irregular quadrangular primary meshes; ultimate meshes variablenbsp;in size, distinctly defined, and formed chiefly by the meeting of the nervesnbsp;under large angles.

This leaf of moderate size is noteworthy for the great thickness of its midrib, the unusual slenderness of its primary nerves, and the irregularitynbsp;of its nervation. This, like the preceding, belongs to the elongate sectionnbsp;of Frotemphjllum. The leaf seems to have been somewhat inequilateral.nbsp;The nervation has some of the characters of the Celastrinece, as shown in G.nbsp;Scandens.

Leaves rather large, oval-elliptical in form, subacute at summit, rapidly rounded at base, and then narrowed gradually into the petiole; midnerve very thick, and apparently somewhat succulent; primary lateral nerves very slender, going oflP at an oblique angle, arching upwards ap-

proximately parallel to the margin for some distance, not meeting one another; the primary nerves sending off branches in a dichotomous manner,nbsp;and these anastomosing to form large, irregular, lax primary meshes; thenbsp;ultimate meshes, elongate and mostly quadrangular, rather indistinctly defined, owing to the thick leaf-substance.

The nervation of this plant is more like that of Protcaipliyllum ovatuni than any other in the size and loose texture of the midnerve, the slendernbsp;primary nerves, and the irregular lax nervation ; it is proteaceous, but combines with the characters of the Froteacece some of those of the Celastrincce.nbsp;Indeed, we may say generally of the leaves of Froteceplujlliim with a midrib, that they combine features of the nervation of both these genera. Thisnbsp;species may be compared witli Fersoonia daphnoides. It belongs to the elongate section o'f Froteonpliyllim. Fig. 2 is a restoration from several specimens.

Shape of leaf unknown ; leaves apparently of large size and elongate . leaf-substance thick ; midnerve extremely thick, loose-textured, and apparently somewhat succulent; primary nerves extremely slender, going off atnbsp;a more or less acute angle, then arching backwards and splitting up intonbsp;brandies that are nearly as strong as the primary nerves. These branchesnbsp;meet obliquely to form oblong or elliptical irregular primary meshes ofnbsp;large size ; ultimate nervation not visible.

Localities : Fishing hut above Dutch Gap Canal; road-side near Potomac Run; rare.

These leaves are remarkable for the striking contrast in the size of the midnerve and the primary nerves, ddiey really possess no distinct primarynbsp;nerves. The nervation is a good deal like that of some Fersoonias. Thenbsp;leaf must have been very large.

Leaves small, orbicular in outline ; leaf substance thin, margins cut into acute or subacute ovate teeth, which are directed forwards, and are of vary-

ing but always small depth; no midi-ib seen ; the base and summit of the leaves not foiind; the nerves very slender and seen with difficulty, they arenbsp;several in number, of about the same strength, and appear to diverge fromnbsp;tlie base of the leaf with a flexuous course; they unite to form a seriesnbsp;of large, elongate, subrhombic meshes; slender branches appear to enternbsp;each tooth.

This species is one of the abundant plants at these localities. The leaf-fragment, PI. CLXXII, Fig. 4, is very imperfect, since the margins have all been removed. The shape of these leaves is more like that of some of thenbsp;species of Frotea, while the nervation resembles that of some of the speciesnbsp;of Persoonia.

Leaves long, narrow, and willow-like, wedge-shaped at base, acute, with a very strong midnerve and very slender primary nerves ; these go off verynbsp;obliquely and diverge very slowly from the midrib, running for a long distance nearly parallel with the margins of tlie leaves; they anastomose withnbsp;branches sent off from other nerves of like grade higher up to form verynbsp;long, irregularly shaj^ed, and lax meshes; ultimate reticulation oblong, sub-rhombic, of quite uniform dimensions This genus is named for Prof W.nbsp;B. Rogers, who first called attention to the plants of the Potomac formationnbsp;and studied its geology;

Plate CXXXIX, Fig. 6; Plate CXLIV, Pig. 2; Plate CL, Fig. 1; Plate CLIX, Pigs. 1, 2.

Leaves narrowly elliptical, gradually narrowed to the base and apex, with wedge-shaped base, acute, very long in proportion to width; midribnbsp;comparatively very stout; primary nerves very slender, going off verynbsp;obliquely, proceeding upwards for some distance nearly parallel with thenbsp;margin, but gradually approaching it; primary nerves sending off verynbsp;obliquely secondary nerves, which anastomose with their neighbors tonbsp;form elongate, subrhombic, and irregular meshes, which have their maximumnbsp;dimensions turned upwards and slightly outwards; primary meshes filled

witli pretty sharply defined ultimate meshes, polygonal in shape, and varying in the number of sides from four to six.

Localities: Fishing hut above Dutch Gap Canal; Fredericksburg; Kankey�s; rare.

The shape of these leaves is a good deal like that of Salix. The midnerve is in size out of all proportion to the primary nerves sent offnbsp;from it. In its primary nerves and in the shape of the leaf the plant is anbsp;good deal like Glossochlamys transmutans Ettingshausen and Gardiner.^ Thenbsp;resemblance in leaf-form and nervation to Persoonia mollis R. Brown isnbsp;strong. The affinities of the plants of this genus seem to be with thenbsp;Proteacece.

Leaves �'narrow, small, very elongate-oblong, narrowed gradually to the base and apex, subacute, sometimes curved ensiform; midnerve proportionally very strong, with a thick petiole; lateral or primary nervesnbsp;very slender, going off at an acute angle and arching up towards the summit, forming more or less persistent nerves approximately parallel with thenbsp;margin, and having a flexuous course. They send off very obliquely slender lateral nerves, which anastomose with the adjacent ones, and formnbsp;irregular, elongate, polygonal meshes, with their longer dimensions directednbsp;upwards. The latter, by splitting up into ultimate nerves, form an irreg-ulai*, lax, ultimate net-work.

This is the most common angiosperm at Fredericksburg, and it is rather abundant there. It has leaves shaped much like some forms ofnbsp;Salix, but the nervation is different. The midnerve is remarkable for itsnbsp;great proportional strength. The nervation is usually so fine that evennbsp;the primary nerves are seen with difficulty. The leaf-substance seems tonbsp;have been thick and the epidermis firm and durable, so that the leaves arenbsp;generally well preserved.

In the shape and nervation of the leaves this plant may be compared with Persoonia mollis R. Brown.

The genus Sassafras seems to have been certainly present in the Potomac flora in forms that differ little from the living species, and in atnbsp;least one species the fossil leaves can be matched by the living plantsnbsp;which abound in the vicinity. The genus, however, is sparingly represented both in species and individuals. Remarkably few specimens ofnbsp;undoubted Sassafras were found.

Leaf very small, shape not seen. At the summit there is an obtusely rounded short lobe, and on each side of this occur two oval subacute lobesnbsp;which are imperfectly shown, owing to mutilation.

Leaves small, but varying somewhat in size, wedge-shaped at base, expanding rapidly above so as to assume a fan-shape, having at the summit three lobes, which extend nearly to the same height, but are very shallow. The middle one has its margins parallel with the midrib for thenbsp;greater portion of its length, but at its summit it is abruptly rounded andnbsp;very obtuse, or else narrows to a subacute point; the lateral ones are separated from this by a rather broad, rounded sinus, and have their tips morenbsp;or less divergent, subacute, pretty broad, with the outer margin curvingnbsp;gently and the inner nearly straight. The petiole seems to have beennbsp;strong, and soon after entering the leaf it splits into three nerves, onenbsp;medial and two lateral; lateral nerves going off obliquely at nearly thenbsp;same point and running nearly straight into the lateral lobes, each sendingnbsp;off on the outer side, near the base and at the same height, two strongnbsp;branches, that curve upwards; lateral nerves at higher points and the midnerve throughout, sending off obliquely lateral nerves that are muchnbsp;smaller than the two lower outer ones. Subordinate nerves and reticula-MOW XV--19

tion not seen; leaves thick, and the lamina of the leaf decurrent for a short distance on the petiole, forming a narrowing wing.

This plant seems to be a variety of Sassafras cretaceum Newb., from the Cretaceous of Dakota, but the nerves are more slender and the terminalnbsp;lobes different from the normal species. It is a good deal like S. parvifolium,nbsp;from Covington street, Baltimore, but is much larger.

Leaf-substance moderately thick; leaf rather large, elliptical-shaped at base, cut into a rather long lateral lobe, ovate in shape, which is turnednbsp;away from the midrib, having the opposite side of the leaf gently roundednbsp;off; terminal lobe much larger, ovate in shape; midnerve strong, sending offnbsp;on the right-hand side from near the base and into the lateral lobe a strongnbsp;nerve, and on the left-hand side from a little higher a smaller one, whichnbsp;curves upwards, following the margin of the leaf for some distance; thenbsp;midnerve above the base at different points sends off minor nerves, whichnbsp;curve upwards and fork ; ultimate nervation not seen.

This plant is strikingly like some leaves of the living species of Sassafras, in which we occasionally find leaves with a single lateral lobe, just like that in the fossil. Among fossils it is nearest to S. recurvatum, Lesq.,nbsp;from the Cretaceous of the Dakota group.^ The fine form, PI. CLXIV,nbsp;Fig. 4, was found at the 72d mile-post. Only one specimen was discoverednbsp;here. It is quite possible that if more had been found some of them wouldnbsp;have shown two lateral lobes, for the size of the lowest lateral nerve, onnbsp;the left-hand side of the leaf, although inferior to the corresponding one onnbsp;the right hand, indicates that the plan of the leaf calls for two lateral lobes.

Leaves elliptical in outline, subacute, gradually narrowed at base, with the lamina of the leaf more or less decurrent along the petiole; midnerve

and petiole extremely thick proportionally; lateral or primary nerves proportionally and in most of the forms absolutely slender, extremely irregular in arrangement, forming a lax reticulation of very archaic type. Ultimatenbsp;reticulation strongly marked and fern-like.

This genus is an important one in the Potomac flora, and has contributed a considerable number of individuals to the vegetation of that epoch. It is largely developed in association with Jurassic types of plants,nbsp;as at Fredericksburg, where it is most abundant, and is almost wanting innbsp;the strata where more modern elements abound, as at Brooke, Whitenbsp;House, and Baltimore. As illustrating the archaic and peculiar features ofnbsp;these leaves and those of Frotecephyllum, I may state that for some timenbsp;no other leaves but these were found at Fredericksburg, and finding themnbsp;associated only with plants of Jurassic facies I found it difficult to givenbsp;any good characters distinguishing them from ferns. There is a generalnbsp;and strong resemblance between these plants and some species of Ficus,nbsp;and for this reason it seems best to place them in a new genus, indicatingnbsp;by its name the apparent affinity with that genus. It is quite possible thatnbsp;these are ancestral forms of Ficus.

Plate CXLIV, Fig. 3; Plate CXLV, Fig. 3; Plate CXLVI, Fig. 1; Plate CXLVII, Pig. 4; Plate CXLVIII, Figs. 1, 2, 4; Plate CLVII, Fig. 4; Plate CLXXIIl, Fig. 10.

Leaves large, of varying size, sometimes attaining very large dimensions, elliptical in outline, subacute, with tips often broadly wedge-shaped, rounded off gradually at base, and narrowed slowly into the petiole. Midrib very stout, woody, and strong nearly to the tip of the leaf, rathernbsp;vaguely defined, and apparently somewhat succulent; primary nerves innbsp;proportion to the mid-rib slender, but compared with those of the othernbsp;species of the genus thick; they go off on each side of the midrib, mostlynbsp;very obliquely, subopposite or alternate, arch backwards and then stronglynbsp;forwards, curving around so as to connect with the next nerves of the samenbsp;rank; they send off on the outer side branches which continue for somenbsp;distance curving towards the summit and gradually approaching thenbsp;margin; between the main lateral nerves, which are usually thick andnbsp;strongly marked, subordinate lateral ones are commonly shown, as in PI.

CXLIV, Fig. 3, PI. CXLVII, Fig. 4. These unite with the main lateral nerves or the larger branches from them, and form very large, irregularly-shaped, lax meshes. Sometimes the principal net-work in the interspacesnbsp;of the main lateral nerves is formed by large branches from these; thenbsp;union of the principal lateral nerves, or of their main branches, makes anbsp;row of well-defined arches near the margin of the leaf; the ultimate meshesnbsp;are quite uniform in size, mostly subrhombic in form, and not so sharplynbsp;defined as in most of the types with archaic forms of nervation from Fredericksburg.

Localities; Fredericksburg, quite common; Deep Bottom; fishing hut above Dutch Dap Canal, rare.

This singular plant must have had in some of its leaves a very great size. This is indicated by such fragments of leaves as are shown in PI.nbsp;CXLIV, Fig. 3, and PI. CXLVII, Fig. 4, both of natui�al size. The midribnbsp;especially is conspicuous for its great thickness. It, and especially itsnbsp;extension as the petiole, seem to have been somewhat succulent. This wasnbsp;much the largest species of leaf found at Fredericksburg. As these archaic-looking leaves were the first ones found, and as I found it difficult to givenbsp;any characters which would distinguish them from ferns, I have given thenbsp;details of their nervation more fully than I would have done if the presencenbsp;of angiosperms had then been fully established in the Potomac flora. Upnbsp;to this time these strata have been held by most persons to be Triassic.

The leaf, PI. CXL, Fig. 3, shows what might at first sight seem to be a petiole, but it is really a portion of the midrib from which the lamina ofnbsp;the leaf has been stripped, and tbe basal portion of the lamina, still shown,nbsp;is doubled back and contorted. Plate CXLVIII, Figs. 1, 2, shows leavesnbsp;of the smallest size.

The nervation of these leaves is a good deal like that of Dawson�s Ficus maxima, Cretaceous and Tertiary Floras of British Columbia.

Plate CXL, Fig. 3; Plate CXLI, Fig. 2; Plato CXLV, Pigs. 1, 4; Plate CXLVII, Pig. 2; Plate

Leaves varying in size, sometimes attaining very considerable dimensions, oval in outline, rapidly rounded off towards the base, where it is

widest, and then gradually naiTowed to the petiole, subacute at the tip, where the margins for some distance down are generally straight; midribnbsp;compai�atively very thick, and apparently somewhat succulent; petiolenbsp;somewhat succulent and very thick; the leaves probably pinnately arranged ; primary nerves very slender in proportion to the size of the midrib, departing at an angle of about 45�, arching around to connect withnbsp;those next above, and sending off branches mostly on the outer side, forming by their union several series of arches between the midrib and the margin ; between the main primaries subordinate ones spring from the midrib,nbsp;sending off branches to unite with the main primaries; primary net-worknbsp;of nerves formed of the principal branches of the primaries meeting nearlynbsp;at a right angle, composed of large, lax, obtuse-angled meshes, four to sixnbsp;sided ; ultimate net-work composed of nerves of uniformly equal strength,nbsp;meshes nearly of the same size, obtuse-angled, and generally four-sided.

The petiole of this plant is, in proportion to the primary nervation, even more massive than that of F. crassinerve. The primary nerves arenbsp;notably slender, and their branches meet more neaidy at a right angle,nbsp;while the series of arches running parallel with the margin are more numerous than in F. crassinerve. Plate CXLI, Fig. 2, indicates that some olnbsp;the leaves must have attained dimensions rivaling those of F. crassinerve.nbsp;This shows well also the straight margins towards the tips of the leaves,nbsp;which are caused here to have a triangular outline. On the other hand,nbsp;the small leaf, PI. OXLIX, Fig. 3, gives a degree of smallness never foundnbsp;in F. crassinerve. The leaves in Fig. 5 of the same plate occur in such anbsp;position as to suggest they were attached in pairs or pinnately. The uppernbsp;leaf, on its left-hand basal margin, has the lamina torn loose and pressednbsp;over on the midrib, while the similarly situated portion of the lower leaf isnbsp;crushed back and doubled over upon itself. This figure shows a greatnbsp;thickness of petiole, but it was evidently somewhat succulent, as it isnbsp;wrinkled and slightly puckered. Plate CXLV, Fig. 4, gives a restorationnbsp;made out from a large number of specimens which give all parts of the leaf,nbsp;so that it may be relied upon as giving a pretty accurate idea of it.

Leaves of medium size, strongly serrate-toothed, teeth often irregular in size, sometimes double, acute, and directed forwards; shape of the leafnbsp;not fully disclosed, but apparently elliptical; midnerve proportionally verynbsp;strong, lateral or primary nerves very slender, not fully disclosed, but apparently forming by the union of the branches of the primary nervesnbsp;irregular large meshes; ultimate nervation not seen.

With the exception of the toothing this leaf is very much like F. ten-uinerve. It is somewhat similar to Quercus JoJmstrupi^ Heer, from the Patoot beds of Greenland, but the Potomac plant is larger and has a different nervation.

Leaves of medium size, narrowed towards the base and summit, rapidly rounded towards the base, prolonged at the summit into an acute or mucro-nate point; leaf-substance very thick, with a dense glossy epidermis ; midnerve proportionally strong and continuing strong to near the summit;nbsp;lateral or primary nerves extremely slender, closely placed, going off atnbsp;nearly equal intervals, subparallel, curving forwards, sending off obliquelynbsp;delicate branches, which split up dichotomously and anastomose to formnbsp;elongate, subrhombic, irregular meshes, ending near the margin in a finenbsp;nerve, which runs for some distance nearly parallel to the margin.

The leaves seem to have been attached in a pinnate manner. In the marginal nerve and the slender primaries it resembles Eucalyptus. It is anbsp;good deal like Ficus magnolicjcfolia Lesq., Ci�etaceous and Tertiary Floras,nbsp;PI. XVII, Figs. 5, 6.

The genus Ficus is represented in the Potomac flora doubtfully by only two species, and these have, so far as found, very few individuals. Ifnbsp;present, it seems to be newly introduced.

Leaves small, elongate-oblong, obtuse, gradually narrowed towards the base into the petiole, so as to form a long, narrow wing along thenbsp;petiole; midrib distinct to the summit; lateral nerves slender, but verynbsp;sharply defined, making a large angle with the petiol� and going off at regular and equal intervals, opposite or subopposite, arching over in a flex-uous manner to unite with those next above, forming a series of well-definednbsp;arches not far from the margin ; branches on the outer side from the archesnbsp;form a flexuous nerve, which runs parallel with and near to the margin, andnbsp;which, by sending branches to the principal arches, forms a series of subordinate ones ; branches sent off from the primaries and from the midribnbsp;unite under large angles to make a series of meshes irregular in size andnbsp;polygonal in form; these are filled by the ultimate reticulation, which is.nbsp;as are all the nerves, sharply defined.

This plant, in shape of leaf and nervation, is like some forms of Sapin-dus. It is much like Lesquereux�s Ficus laurophylla,^ but the primary nerves are not so strong and the arches are more pronounced.

Leaves of medium size, oblong or elliptical, subacute; midnerve very strong; primary nerves rather strong, leaving the midnerve alternately atnbsp;an-angle of about 45�, at regular and nearly equal intervals, arching backwards and then forwards until near the margin, where they bend abruptlynbsp;forwards, forming arches by union with the primaries next above ; reticulation not seen.

The plant is a good deal like Sapindopsis elliptica, but the nervation is stronger, and the leaves are larger.

SAPINDOPSIS, gen. nov.

Leaves pinnate, both odd pinnate and abruptly pinnate ; terminal leaves usually more or less united at base ; upper pairs of leaves decurrent, forming a wing on the common stem, the wing lessening in width on the pairsnbsp;in descending; leaves mostly opposite in pairs, sometimes subopposite ;nbsp;the lowest pairs lack the wing, and are sometimes short-petioled; leavesnbsp;thick, with dense and often glossy epidermis, elliptical or lancet-shaped,nbsp;with a strong prominent midrib, which extends with slight diminution to thenbsp;tip of the leaf; lateral nerves going off at a largo angle, and uniting morenbsp;or less completely near the margin to form a series of arches; the lateralnbsp;or primary nerves, as seen on the lower side of the leaves, strong and prominent, but on the upper side, owing to the thickness of the leaves, generallynbsp;indistinct; the ultimate reticulation is strong, and forms a series of rathernbsp;large, irreg-ulai�, polygonal meshes.

This genus is a very important one in the strata containing the more recent types of plants, especially as seen at the two Brooke localities and atnbsp;White House. It has furni.shed an immense number of individuals, formingnbsp;at these places the predominant fossils. The upper leaves, perhaps owingnbsp;to the presence of the wings, seem to have been very persistent. It isnbsp;probable that, normally in all cases, the lowest leaflets on the compoundnbsp;leaf were petioled, but, perhaps owing to this fact, they are by no means sonbsp;commonly found attached to the stems as the upper ones. The leaves arenbsp;so much like those of Sapindus that jjerhaps they might with propriety benbsp;placed in that genus. They seem to be at least ancestral forms of Sapindus.nbsp;The leaves of some species seem to be Amry variable within certain limits.

Leaf small, oblong with a subcordate base of thick consistency; midnerve and petiole strong, nervation mostly concealed by the thickness of the leaves ; primary nerves as seen very slender, going off at an angle ofnbsp;about 45�, and half-way to the margin bending suddenly forward to connectnbsp;with the next primaries, sending off at the point of sudden bending a branchnbsp;which connects with the next lower primary.

The thick leaf-substance and the dense glossy epidermis obscure the nerves. The leaf figured seems to be one of the lower petioled ones, andnbsp;apparently presents its lower face uppermost.

Leaves elongate, elliptical, narrowed gradually towards the base and apex; midnerve strong and prominent; primary lateral nerves slender butnbsp;distinct, going off at an angle of about 45�, arching backwards slightly andnbsp;then forwards, and then at three-fourths of the distance to the margin abruptly turned forwards to unite with the next primaries to form a series ofnbsp;arches which run parallel with the margin and near to it; intervening minornbsp;nerves leave the midnerve, as do the primaries, and unite mostly with thenbsp;middle points of the arches ; ultimate reticulation distinct, composed of proportionally large, irregular, polygonal meshes.

The plant is much like Sapindus in the form of the leaf and in the nervation. It has some of the features of Ficus lauropliylla} Lesq.

Plate CLl, Figs. 2, 3; Plate CLII, Figs. 2, 3; Plate CLIII, Fig. 2; Plate CLIV, Figs. 1, 5; Plate

Leaves odd-pinnate, leaf-substance thick and leathery, epidermis thick and glossy; leaflets comparatively large, lancet-shaped to elongate-elliptical, subacute, upper pair and terminal leaflet sometimes united for somenbsp;distance; uppermost pair of leaflets mostly decurrent on the lower side bynbsp;a broad wing, on the upper side cut away nearly or quite to the midrib,nbsp;wings diminishing in width on the leaflets in descending, lowest pairs of leaflets short-petioled; leaflets placed opposite or subopposite in jiairs; mid-nerve very stout, rounded, and prominent, continuing strong to the tip ofnbsp;the leaflets; primary nerves comparatively slender, conspicuous only on thenbsp;under sides of the leaflets; the primary nerves go off pinnately at about

an angle of 45�, arcli at first slightly forwards, and then bend strongly forwards to form arching nerves, which run for some distance approximately parallel to the margin, gradually approaching it; these communicate withnbsp;one another by one strong nerve each to form large spaces approximatelynbsp;pentagonal in form, and by a series of minor nerves, which meet at a largenbsp;angle, connect with tlie midrib and primary nerves to form quadrangular ornbsp;subrhombic primary meshes; the ultimate meshes quadrangular or sub-rhombic and comparatively distinct.

This plant is very common at all these localities. It, with S. variabilis, makes up the greater part of the fossils at these places. The plant is muchnbsp;like S. variabilis., and may possibly be a large variety of it. The leaves,nbsp;however, are uniformly thicker in substance than those of that species.nbsp;They sho'wr a greater tendency to short, broad forms, and the midnerve continues remarkably strong to the tips of the leaves. The chief cause of separation is the nervation, which is quite different from that of 8. variabilis,nbsp;lacking the distinct connecting marginal and arching nerve seen in thatnbsp;species. Fragments found indicate leaflets larger than any of those figured.nbsp;Plate CLIV, Fig. 5, shows an abnormally short thick leaf. It may possibly be the terminal one, for this is sometimes different from those lowernbsp;down. Plate CLII, Fig. 3, gives a pair of large leaves which remind one ofnbsp;Hymencea, but they are the terminal leaflet of the compound leaf, and onenbsp;(the right-hand) lateral leaflet; the other lateral leaflet on the left-handnbsp;side has been accidentally torn away.

Plate CLI, Fig. 1; Plate CLII, Figs. 1, 4 ; Plate CLIII, Pig. 3; Plate CLIV, Figs. 2-4; Plate CLV,

Leaves and leaflets small; leaflets, especially the upper one's, varying much in size, shape, and mode of arrangement; leaves odd or abruptlynbsp;pinnate ; leaflets narrowly elliptical to lancet-shaped ; leaf-substance leathery and thick, epidermis dense and glossy; leaflets normally opposite ornbsp;subopposite, upper leaflets decurrent normally by a narrow wing, but oftennbsp;losing these features; the wing diminishes in width on the pairs descending,

until the lowest pairs are sliort-petioled; midrib and nerves as seen on the under side prominent and sharply defined; midrib stout at base, butnbsp;towards tlie summit rapidly attenuated; lateral primary nerves going offnbsp;])innately at uniform and nearly equal intervals, proportionally very strong,nbsp;at first inclining slightly forwards, and then three-fourths of the distancenbsp;to the margin bending abruptly forwards at nearly a, right angle, to form anbsp;bow-shaped, strong nerve, which connects with the next primary at thenbsp;angle made by it, thus forming a series of arches; this marginal nerve andnbsp;the primaries send off nearly at right angles a series of branches which arenbsp;proportionally very strong and distinct, forming the primary reticulation.nbsp;They unite nearly at right angles, and form four to six sided primary meshes;nbsp;the ultimate meshes are of the same general character, but smaller.

This is the most abundant angiosperm at the last-named locality. It is very common at the two Brooke localities, but is not so abundant therenbsp;as S. magnifolia. Tliis plant is very variable, and shows a curious fluctuation between odd and abruptly pinnate leaves and an alternate or oppositenbsp;arrangement of the leaflets, as if the habit of the plant was not yet fixed.nbsp;Plate CLII, Figs. 1, 4, seems to give the normal mode of arrangement ofnbsp;the leaves; i, e., they are odd-pinnate, with the lower leaves in pairs. Innbsp;none of the species, however, does the odd or abruptly pinnate mode ofnbsp;arrangement of tlie terminal leaves seem to mean anything or to be fixed.

I have given a number of figures of abnormal forms of this plant to illustrate its variability. PI. CLIV, Fig. 2, shows union of the threenbsp;terminal leaves and the decurrence of the two outer or lower ones bynbsp;means of a very wide wing. The next lower pair of leaves are narrowlynbsp;decurrent and normally paired. Fig. 4 of the same plate shows thenbsp;decurrence of the uppermost leaves, but the leaves next below are notnbsp;paired, and are unequally winged. The next lower leaf stands alone andnbsp;the stem is quite flexuous. Fig. 3 of the same plate shows two terminalnbsp;leaves united and decurrent to the next lower one on the left-hand side,nbsp;which is single, and uniting with it at base. On the right-hand side thenbsp;terminal leaf on that side is decurrent to the paired leaves below, withnbsp;which, however, it does not unite. PI. OLV, Fig. 4, shows a terminal

decurrent pair, and the following ones lower down, widely separated, and alternate. PI. CLIII, Fig. 3, shows what seems to be the base of thenbsp;common petiole, and it looks as if it were clasping. This figure, however,nbsp;has the abnormal character of possessing only three leaves and all of themnbsp;terminal, the only case of the kind seen.

Leaves and leaflets very small, leaves odd-pinnate; terminal leaflet much larger than the others, united with the right-hand next lower leaflet;nbsp;uppermost leaflets subopposite, long-decurrent, united by a narrow wingnbsp;with the pair next belov/-; second pair from the top subopposite, slightlynbsp;decurrent, not reaching to the next pair; last or third pair subpetioled;nbsp;midnerves comparatively strong, other nervation not seen; leaves ellipticalnbsp;in shape, subacute, with the lamina of the leaf cut away obliquely on thenbsp;upper side; leaf-substance thick and leathery.

Leaves odd-pinnate, terminal leaflet usually the largest; leaf-substance thick and leathery, obscuring the nerves; terminal leaflet oval or elliptical,nbsp;sometimes slightly inequilateral, very wide in proportion to length; lowernbsp;paired leaflets elliptical in shape, very short in proportion to the width,nbsp;sometimes slightly falcate, subacute or obtuse; upper pair cut awaynbsp;obliquely on the upper side nearly or quite to the midrib, decurrent onnbsp;the lower side, or subpetioled; midnerve strong, lateral nerves not fullynbsp;shown; the primaries are pinnately arranged, go off at equal intervals, andnbsp;arch slightly forward, the lower portions alone being seen.

This plant shows some variation, but not enough to cause a separation into distinct species. In PI. CLXIII, Fig. 3, the terminal leaflets, all that

were seen, are closely crowded, so that the lateral ones overlap the terminal one; the leaves are elliptical, and the nerves are stronger than in any ofnbsp;the other specimens. In PI. CLIII, Fig. 4, and PI. CLV, Fig. 7, thenbsp;terminal leaflet is distinctly petioled and comparatively remote from thenbsp;lower ones, which also are furnished with petioles. This seems to be quitenbsp;a distinct species from the preceding.

Leaves odd-pinnate, summits of the leaflets not seen, but they are apparently of considerable size ; leaflets narrowed gradually at their bases, more so in the lower ones, which are wedge-shaped at base, and the lowest pairnbsp;petioled; uppermost pair of leaflets slightly united to the terminal one,nbsp;and this latter larger than the others and less narrowed at base; uppermostnbsp;leaflets cut away obliquely at base on the upper side nearly to the midrib,nbsp;decurrent on the lower side, with a narrowing wing to the next pair, butnbsp;not uniting with it; next lower pair very slightly decurrent, and wedge-shaped at base ; leaflets quite remote, the leaf-substance thick and leathery;nbsp;epidermis firm and glossy ; midnerves comparatively slender; lateral primarynbsp;nerves slender; the lowest primary nerves go off very obliquely and runnbsp;approximately parallel with the margin for some distance; succeeding primaries go off at more obtuse angles until towards the middle of the leafletnbsp;they go off at right angles; towards the margins of the leaflet they bendnbsp;abruptly forwards and connect with the next higher primaries, forming anbsp;series of arches; intermediate subordinate nerves go off from the midnerve,nbsp;and send off branches which anastomose with branches from the primaries,nbsp;forming finally an ultimate reticulation mostly subrhombic in shape; nervation all quite slender and the reticulation lax.

Leaf-substance very thick; leaflets glossy, oblong, rounded, and very obtuse at the tips, often slightly inequilateral, that is, the midnerve does

not divide the leaves exactly in half; midnerve stout, rigid, and rounded; lateral primary nerves very slender, not fully disclosed, going off at smallnbsp;intervals from the midrib at an angle of about 45�, arching slightly forwardnbsp;to near the margin, and then abruptly bending forwards to connect with thenbsp;next primary at its sudden bend, the connecting nerves forming a marginalnbsp;one; ultimate reticulation not made out.

Localities : Deep Bottom ; 72d mile-post, near Brooke ; not very rare at the latter place.

I group under this liead a number of leaves imperfectly preserved and of doubtful affinity owing to the poor preservation of the nerves. In thenbsp;nervation, so far as it could be made out, and in the shape of the leaves,nbsp;they appear to be nearer Salix than any other genus. The leaves may benbsp;described as elongate-elliptical in outline, with midnerves strong at basenbsp;and much attenuated towards the summit; lateral nerves slender, the primaries going off very obliquely and curving strongly towards the summitnbsp;of the leaf, continuing approximately parallel with the margin, but gradually approaching it.

This genus has furnished a considerable element to the Potomac flora, the plants being chiefly found in the strata showing the flora with morenbsp;recent aspects.

Leaves small, oblong elliptical, very long in proportion to their width, summit not seen, gradually narrowed towards the base; midnerve towardsnbsp;the base very strong, attenuated above; lateral nerves slender; primarynbsp;nerves going off at an acute angle, inclining forward to near the margin,nbsp;then abruptly bent forward to form an arch which is approximately parallelnbsp;with the margin, this connecting with the next primary above at the pointnbsp;where it suddenly bends; the successive arches make a continuous sinuousnbsp;marginal nerve, which is as strong as the primaries connected by it; intercalated subordinate nerves from the midrib send off branches which unite

with those of the primaries, and finally form the ultimate meshes, which are irregular in form and size, quite large, and mostly subrhombic in form.

The shape and nervation of this leaf remind one strongly of Salix. It has also a good deal of likeness to Persoonia daphnoides.

Plate CXLVI, Figs. 2, 4; Plate CL, Fig. 8; Plate CLXIII, Pig. 5; Plate CLXVI, Pig. 2.

Leaves elliptical in outline, small, broad in proportion to their length, narrowed gradually at the base and summit, acute; midnerve strong atnbsp;base and attenuated at the summit; primary lateral nerves going olf at anbsp;very acute angle, arching strongly forwards; ultimate nervation not seen.

Localities: Fishing hut above Dutch Gap Canal; Fredericksburg; 72d mile-post, near Brooke; rare.

Angiosperms are very rare at the fishing hut above Dutch Gap Canal. This fossil is the most common of those at this place. The leaf-substancenbsp;appears to have been quite thick, and so was the epidermis, so that thisnbsp;latter was quite durable. It was owing to this character of the leaf thatnbsp;the finer nervation was concealed.

Leaf very small, broadly elliptical, acute, narrowed at base and apex; petiole proportionally very strong, expanded below with a wing as if duenbsp;to stipules or to a clasping mode of attachment; midnerve very slender,nbsp;lateral nerves going off very obliquely and curving upwards, only partially seen ; ultimate reticulation not seen.

Leaves small, elliptical in shape, margins toothed or entire; midnerves slender; primary nerves very slender, going off obliquely and pinnately,nbsp;curving up towards the apex, connected by comparatively strong nerves.

which run nearly at right angles with the connected nerves, forming an irregular, slender, lax reticulation ; ultimate reticulation not seen ; leaf-substance mostly thin.

Under the head of Celastrophyllimi I group a number of small leaves, which mostly have the nervation too slender and poorly preserved to enablenbsp;one to fix the character with any definiteness. The placing of these in anbsp;group based on affinities with the Celastrinece is of course, under such circumstances, only provisional. On the whole, the general character ofnbsp;these leaves is nearer to Celastrus than to any other living plant. Theynbsp;form a considerable element in the Potomac flora, although no species furnishes, so far as found, any great number of individuals.

Shape'of leaf not seen, probably oval or elliptical; midnerve comparatively strong ; leaf-substance thin ; primary nerves very slender hut comparatively distinct, going off at an acute angle and curving strongly upwards towards the tip of the leaf, running for a long distance parallel to onenbsp;another, and gradually nearing the margin, bent into a series of how-shaped arches, which are connected by a regular series of cross-bars ornbsp;nerves, going off nearly at right angles and forming a series of large pentagonal meshes filled by small nearly rectangular meshes; the ultimatenbsp;reticulation formed of mainly pentagonal or hexagonal meshes.

This plant differs in some points of the nervation from the others grouped under the head of CelastropJiyllum, except perhaps C. latifolium., tonbsp;be described later. It is on the whole considerably like Celastrus trigynus,nbsp;and also resembles C. ruber.

Leaf small, elongate-elliptical, narrowed gradually to the base into the petiole; leaf-substance thin; no nerves seen; they must be very slender.

Only one specimen was found. The leaf is too imperfectly shown to enable its character to he made out. It may he compared with Celastrusnbsp;Senegalensis.

Leaves small, narrowly-elliptical; leaf-suhstance comparatively thick ; margins with acute, shallow, and small teeth, that are curved forwards;nbsp;midnerve proportionally quite strong; lateral nerves very slender, goingnbsp;off at an angle of about 45�, curving forwards and forking dichotomously,nbsp;very po'orly disclosed; reticulation not seen.

This plant looks something like a Banksia in its toothing and in the shape of the leaf.

Leaves rather large, with a comparatively thick and firm leaf-substance, apparently elliptical in shape, having on the margins of the leaves shallow,nbsp;obtusely-rounded teeth, turned outwards and very closely. placed; midnerve proportionally quite thick ; primary nerves very slender, going offnbsp;obliquely and curving forwards, the bases only being seen; ultimate nervation not visible.

This plant also resembles Banksia in the peculiar teeth and the very slender primary nervation. The teeth have been accidentally removed,nbsp;except at the summit of the leaf. It is close to C. acutidens, and may be anbsp;variety of it.

Leaves of medium size, varying considerably in dimensions, narrowed towards the base, so as to give them a wedge-shaped form, swelling rapidlynbsp;out in the middle to a broad elliptical shape ; towards the summit narrowednbsp;rapidly and prolonged to a point probably; midnerve very distinct, lateral

primaries going off at equal intervals, very strongly curved upwards; minor nerves not seen ; leaf-substance thick.

Leaf very small, elliptical to ovate in shape, acute; margins minutely dentate; midnerve slender, lateral nerves going off obliquely and curvingnbsp;up, very slender, lower ones more oblique and arching more strongly thannbsp;the upper ones; ultimate nervation not seen.

Leaves very small, broadly elliptical to nearly orbicular, obtuse at summit, flared out in the middle, narrowed to the base ; leaf-substance verynbsp;thin ; midnerve slender, attenuated towards the summit; lateral nerves verynbsp;slender, going off very obliquely, and curving in a circular manner towardsnbsp;the tip of the leaf, opposite, connected by transverse nerves, that go offnbsp;nearly at right angles and make quadrangular subrliombic meshes; ultimatenbsp;reticulation not seen.

These leaves are quite common at the Baltimore localities. In shape and nervation they are much like the living plant Celastrus nutans. Thenbsp;leaf given in PL CLXXIII, Fig. 13, is a good deal like C. arcinerve in thenbsp;jieculiar nervation, but it is smaller and more delicate.

Leaf very small, probably orbicular in shape, rounded abruptly at base; midnerve comparatively strong; primary nerves imperfectly shown, verynbsp;slender, going off at rather a large angle, tending outwards and then up-

wards, branching apparently in a dichotomous manner; ultimate reticulation not seen; leaf-substance very thin.

Leaf-substance very thin; leaves small, rounded, and very obtuse at summit, narrowed gradually to the base, obovate in shape ; midnerve strongnbsp;at base, much attenuated towards the summit; lateral nerves very slender,nbsp;going off very obliquely and curving around towards the summit, flexuousnbsp;in their course and sending olf obliquely branches which connect eithernbsp;with other branches or with the primaries, forming large, elongate, subrhom-bic meshes; ultimate nervation not seen.

This leaf is much like that of Emnymus frigidus. It is also like that of Gelastrus obovatus, but the nervation is different.

Leaves small, wedge-shaped at base; leaf-substance thick, with strong ovate teeth directed forwards; midnerve strong at base, rapidly attenuatednbsp;above; lateral or primary nerves sometimes slender, going off very obliquelynbsp;and curving forwards, forking dichotomously; ultimate nervation not seen.

The leaves placed in this genus, from their affinity with Quercus, are rare and unimportant, since they play but a very small part in the Potomacnbsp;flora. The amount of material found is too small, and the degree of preservation too poor, to permit their character to be definitely fixed.

Leaf small, entire shape not shown ; margin furnished with very large ovate, acute, unequal teeth, that are turned upwards; midnerve quite strongnbsp;towards the base, much attenuated above, and splitting up into the primarynbsp;nerves ; primary nerves subopposite, strong at base, forking dichotomously.

Leaves elliptical, narrowed towards the apex and base, wedge-shaped at base; margins beginning some distance from the base, serrate-toothed,nbsp;with the teeth directed forwards; midnerve strong towards the base; primary nerves very slender, going otf at a very acute angle, and arching forwards to end in the teeth, sending off obliquely on each side alternate, verynbsp;slender, subordinate nerves; ultimate reticulation not seen.

Leaves small, approximately fan-shaped, cut to different depths into obtuse, flabellately arranged lobes of varying shapes and size; nervesnbsp;mostly radiating from the top of the petiole, the main ones generally threenbsp;in number, the middle one being the strongest; petioles very long andnbsp;comparatively stout. The leaves, which I group under this head from theirnbsp;general I�esemblance to Vitis, form a very considerable element in the Potomac flora as found in the beds at Baltimore. They are abundant there andnbsp;are the most common plants at that locality. They have most affinity withnbsp;some of the fossils described by authors under the name Cissites.

Form of leaves not made out, as only segments were seen; principal segments of comparatively large size, incised obliquely into oblong-obtusenbsp;lobes, which in turn are notched at the summit to form two or three slial-low obtuse lobes; nerves going off obliquely one into each main lobe,nbsp;slender and imperfectly shown, only one branch seen in each lobe; leaf-substance very thick ; ultimate nervation not seen.

The specimens shown in Figs. 9, 10, seem to be fragments of principal or primary segments of the leaf, probably the middle one.

Leaves very small, arranged alternately and rather remotely on very long and proportionally stout petioles, more or less fan-shaped, quite variable in form and size, cut down to near the base into tliree main lobes, andnbsp;these subdivided again towards the summit into lobes or teeth, whichnbsp;diverge slightly; primary nerves three, radiating from the summit of thenbsp;petiole, the middle one being the strongest, each going into a main lobe;nbsp;the primary nerves send off obliquely branches which go into the subordinate lobes or teeth.

This is a very peculiar Cissiis-like leaf, which in some of its forms is not unlike Symphoea polymorpha R. Br.

Leaves small, varying a good deal in size and shape, broadly fanshaped to subrotundate, more or less heart-shaped at base, cut generally pretty deeply into three principal lobes separated by sinuses that turnnbsp;slightly outwards; these in turn are subdivided variously; in the largernbsp;leaves they are cut into subordinate lobes that are like the principal ones,nbsp;but are cut less deeply; the larger lobes terminate in shallow lobes ornbsp;teeth that are mostly bluntly rounded olF or emarginate; primary nervesnbsp;normally radiating flabellately from near the base of the leaf and goingnbsp;into the principal lobes, the lowest ones being smallest and increasingnbsp;inwards to the central one, which is the largest; the primaries sending offnbsp;obliquely branches on each side which go into the ultimate lobes and teeth;nbsp;reticulation not seen; leaf-substance quite thick; petiole very long andnbsp;proportionally quite stout.

This plant is the most common angiosperm at the two Baltimore localities. Some of the leaves must have attained proportionally a considerable

size, as indicated by PI CLXXTII, Fig. 2. That shown in Fig. 5 of the same plate seems in lobing and nervation somewhat different from thenbsp;others.

The genus Myrica is represented in the Potomac flora by only one doubtful species, and this is exceedingly rare.

Leaves quite small, elliptical in outline, acute, narrowed to the base, pinnate, margins beginning a little above the base, serrated with smallnbsp;acute teeth directed forwards; petiole quite short; midrib rather stout atnbsp;base, much and rapidly attenuated above; primary nerves slender, leavingnbsp;the midrib obliquely curving upwards and following the margins for somenbsp;distance, connected with one another by nerves that go off nearly at rightnbsp;angles; ultimate nerves not seen.

This genus also has one doubtful and very sparingly developed species. The leaf placed in this g�nus occurs very rarely.

Leaf small, oblong, tip not seen, elliptically rounded at base; midnerve slender; petiole long, slender, and curved to one side, both distinct and prominent; leaf-substance thick and leathery; lateral primary nervesnbsp;going off nearly at right angles, forking about midway in the leaf, sendingnbsp;nerves backwards and forwards, which unite to form pentagonal spaces,nbsp;from the angles of which branches go off nearly perpendicularly towardsnbsp;the margins.

This plant resembles Velenovsky�s Bombax argillacemt} It also resembles in some points Sapindopsis.

Leaves rotimdate; petiole thick and apparently somewhat succulent; nerves tending to a radiate grouping from the summit of the petiole; midnerve not much surpassing in strength the nerves which go oif on each sidenbsp;of it.

The leaves, which I place in this genus from their resemblance to Pop-ulus, are too fragmentary to permit their precise determination. They are always rare, and form no important element of the flora.

Leaves small, reniform, margins crenate; petiole thick and apparently succulent; midnerve hardly stronger than the lateral nerves; primarynbsp;nerves radiating from the base of the leaf, forking freely, and anastomosingnbsp;to form irregular, elongate, subrhombic, or pentagonal meshes; leaf-substance rather thick.

This plant is like ProtecephijUum reniforme, but the margins are slightly crenate, and it has a more pronounced midnerve. It is a good deal likenbsp;Populus retusa,'^ Heer, from Cape Lyell.

Leaf angular and polygonal in outline, small, entire shape not seen; leaf-substance thick and glossy; petiole thick and long, apparently somewhat succulent; no midnerve seen; primary nerves of nearly equalnbsp;strength, radiating from the base of the leaf and forking higher up; ultimate nervation not seen.

�Flor. Foss. Arctica, vol. 4, pt. 1, Beitriige zur foss. Flor. Spitzbergens, PI. XIV, Figs. 6, 7.

This plant is very much like some species of Populus, especially in its petiole, which indicates a tremulous leaf.

Leaf too fragmentary to make out its shape, but apparently very large ; midnerve not much surpassing the size of the lowest primary nervesnbsp;that go off on each side of it, and which, apparently with the midrib, radiate from the base of the leaf; the lowest lateral primaries and the midnerve in its upper portion send off very obliquely strong subordinatenbsp;nerves, which in turn branch, but the further subdivision could not be followed ; the minor nervation not seen.

This leaf differs in the pronounced midnerve and the strong nervation from the otlier species of the genus. Possibly it may be a different genus,nbsp;but in general character it is most like Populus.

Leaves too imperfectly shown in most cases for the shape to be made out; midnerve comparatively strong and promirient; lateral or primarynbsp;nerves opposite or subopposite, strong, and prominent, proceeding straightnbsp;and parallel to near the margin.

The leaves placed under this head belong to only a few species and furnish but few specimens. They have some of the features of Quercus,nbsp;but are on the whole nearer to Ulmus.

Leaves small, oval in shape, subacute; margins cut into subacute shallow teeth that are mostly double; midnerve very strong; lateralnbsp;primary nerves going off very obliquely, subopposite, directed upwards,nbsp;nearly straight and parallel in their course to the margin, the basal pairnbsp;being considerabty the strongest and most branched; the primary nerves

send off obliquely on both sides branches, the largest on the lower side; ultimate branches sent off nearly at right angles from these and from thenbsp;midnerve, which meet under a large angle to form the ultimate reticulation ; this composed of irregular, three to five sided, distinctly markednbsp;meshes; from the base of the lowest primaries on the lower side two strongnbsp;latei�al nerves go off.

The leaf is too fragmentary to make out its shape; midnerve distinct but small; lateral primary nerves going off at equal and regular intervals,nbsp;opposite, and oblique, proceeding straight and parallel towards the margin; branches going off at angles varying from 45� to 90� from the primaries meet and sometimes form a pretty continuous intermediate connecting ultimate nerve ; ultimate reticulation slender, and composed of meshesnbsp;that vary much in size and shape, being angular and four to six sided.

The arrangement of the primaries in this species is much like that in If. crassinerve, but the ultimate nervation is quite different.

Leaf apparently large, form not made out; midnerve moderately strong but very distinct; lateral primary nerves comparatively thick andnbsp;very distinct, leaving at an angle� of 45�, opposite, going straight andnbsp;parallel to the margin; tlie primary nerves send off at right angles branchesnbsp;that fork, with the branches diverging widely and anastomosing to form anbsp;very h-regular net-work that varies much in size and shape; the meshesnbsp;are mostly elongate, witli their largest dimensions perpendicular to thenbsp;primaries.

A good many of the leaves found in the Potomac flora appear to have some affinity with Sterculia, but only one species seems to be near enoughnbsp;to the genus to justify its being placed in it.

Leaves palmately tripartite, the middle lobe largest, subrhombic in shape and acute; lateral lobes elliptical, acute, slightly curved upwards,nbsp;with the lower margin towards the base more convex than the upper, so asnbsp;to give the basal outline of the leaf a subcordate shape; a strong midnervenbsp;runs through the middle of each lobe, the three radiating from the basenbsp;of the leaf; subordinate nervation not seen.

These leaves vary a good deal in size. The base of the leaf has the outline of some Sassafras. PI. CLVII, Fig. 2, is a restoration of the leaf.

ABALIA L.

The genus Aralia, like Sterculia, plays a very unimportant part in the Potomac flora, having, if present at all, only one very doubtful species.

Leaf-substance thick; shape of leaf not made out; leaf divided for some distance down into oblong-elliptical lobes, which at tip are subacutenbsp;and sometimes prolonged into a mucronate point, each lobe having one ornbsp;two midnerves, and from these lateral nerves go off obliquely and remotelynbsp;that arch strongly up towards the tips of the lobes, following the marginnbsp;in their upper course; ultimate nervation not seen.

PI. CLVII, Fig. 1, seems to represent the upper part of a lobe. In Fig. 7 the leaf seems to have been divided into four or five lobes. Thenbsp;right-hand segment, containing two midnerves, seems to be the central lobe.

probably dividing higlier up. The fragment on the left, partly covered by the main^leaf, appears to be a detached lobe, which is wrinkled from pressure. The plant on the whole seems to be nearer to Aralia than to anynbsp;other genus, but it is too poorly preserved to permit its character to benbsp;definitely fixed.

I place under this head a leaf that occurs rarely in the Potomac flora. Its affinities are doubtful, but it seems to be nearer to Juglans than to anynbsp;other genus. The specific description gives the generic description also.

Leaves of medium size, bases not seen, tips oval in outline, prolonged into a tooth-like tip that is turned to one side; leaf-substance thin ; midnerve strong ; primary lateral nerves strong and very distinct, going off atnbsp;regular and equal distances alternately, parallel, arching forward to nearnbsp;the margin, where they are bent abruptly upwards, gradually approachingnbsp;the margin, branches going off at a large angle from these and the midnerve and forking, making by their meeting a set of strong meshes, that arenbsp;elongate, subrhombic, varying much in shape and size, and standing mostlynbsp;at right angles to the main nerves with their longer dimensions; thesenbsp;meshes having sharp angles and very distinct; the ultimate reticulationnbsp;(Fig. 6�^) strong, being made by nerves which meet nearly at a right angle,nbsp;the meshes four to six sided and rotundate.

This plant has some of the features of Persea, and in some respects it resembles some forms of Quercus.

This genus includes plants that stand nearer to Myrica than to any other, yet are not near enough to be placed in that genus. Generic description same as the specific description given below.

Leaves small, linear-oblong, base and summit not seen; margins cut deeply into acute teeth that are turned forwards and often double; leaf-substance thick, leaves quite narrow; midnerve strong; primary nervationnbsp;not seen.

In this genus I place leaves that in general resemble Platanus, but which can not be certainly placed in that genus. The generic description,nbsp;as there is only one species, is essentially the same as that of the species.

Shape of leaf not seen, leaf apparently quite large ; margins not preserved on any specimen; midnerve very strong, especially toward the base ; basal pair of primaries much stronger than those higher, sending offnbsp;on the lower side near the base a strong nerve; the primaries are archednbsp;strongly upwards and send off branches mainly on the lower side; branchesnbsp;going off nearly at right angles connect the primaries, and by forkingnbsp;freely and anastomosing they form subrhombic elongate meshes that standnbsp;with their longer dimensions nearly at right angles with the primaries.

This plant, in the strong lower basal branches sent off from the lower primaries, resembles Aralicephyllmn, but they are not so strong as in thisnbsp;genus. It also resembles Ilederaplatanoides Lesq.

Leaves more or less fan-shaped, divided more or less deeply into three principal lobes, the middle or terminal one subrhombic or elliptical in outline, rapidly narrowed to an acute tip, and separated from the lateral lobesnbsp;by broad sinuses rounded at the bottom; the lateral lobes divided into two

minor lobes, one being larger than the other; the larger one ovate, sometimes inequilateral, and turned upwards; the outer or smaller one is ovate, and turned outwards; the primary nerves three, radiately diverging fromnbsp;the same or nearly the same point at the base of the leaf, going to the summit of each primary lobe; from tlie two lateral primaries a strong branchnbsp;goes off a short distance above the base on the lower side and extends tonbsp;the summit of the outer smaller lobes; all the primaries are strong, and sendnbsp;off on each side branches which curve up and anastomose ; ultimate reticulation not seen.

These leaves are comprehensive in type and unite some of the characters of Liquidamber, Aralia, and Sassafras. In their primary nervation they resemble Sassafras recurvatum,^ Lesq. The lobing is a good deal like that,nbsp;of S. platanoides, Lesq.^ The mode of nervation resembles that of Liquid-amber integrifolium, Lesq.

Leaf-substance thick; leaves rather small, broad fan-shaped in outline, narrowed rapidly at base into the petiole, with a slight decurrence of thenbsp;lamina on the petiole; petiole comparatively very stout, on entering thenbsp;leaf split up into three strong primary nerves, which diverge palmatelynbsp;to go one into each principal lobe; some distance above the point of divergence a strong branch is sent out on the lower side of each lateral primarynbsp;to go into tlifi outermost and smallest lobes; middle lobes broadly elliptical,nbsp;separated from the lateral ones by sinuses that are rounded at base, obtusenbsp;or subacute; lateral principal lobes ovate, or oblong-obtuse, or subacute;nbsp;sometimes inequilateral and curved slightly upwards; minor lateral lobesnbsp;separated from the main ones by wedge-shaped sinuses turned outwards,nbsp;broadly ovate, obtuse, or subacute; branches of small size go off from thenbsp;primaries higher in the leaf in an oblique manner, and curve upwards towards the ends of the lobes.

PI. CLXIII, Fig. 1, differs in several points from PI. CLXIV, Fig. 3, being more like Ar. acutilobum.

Leaves small, broad fan-shaped, rounded off rapidly at base; leaf-substance thick; primary nerves comparatively strong and distinct, the middle one the strongest, three in number, radiating from the base of the leaf;nbsp;leaves cut into three principal lobes; the middle lobe narrowed at the base,nbsp;flared out in the middle-, and narrowed again towards the tip so as to benbsp;broadly elliptical in outline, considerably larger than the lateral ones, separated from the latter by a sinus that is directed outwards and widest at thenbsp;base; main lateral lobes turned at first outwards and then curved slightlynbsp;upwards, inequilateral, with a very convex outer margin furnished with anbsp;short acute tip, almost mucronate ; these main lateral lobes towards the basenbsp;of the leaf incised into an ovate, subacute, short lobe that is turned outwards and slightly downwards; the outer primary nerves, near their base,nbsp;send off a strong branch on the lower side that goes into the outermostnbsp;small lobe or tooth; reticulation not seen.

This plant is a good deal like the preceding species, but seems to be distinct from it.

Leaf very large, but the specimens found are too fragmentary to make out the shape; nerves seen, especially the primaries, very strong; thenbsp;jirimaries, three in number, radiating from the same point at the base of thenbsp;leaf, the middle one being the strongest; the lateral or outermost primariesnbsp;send off some distance above their base a strong nerve on the lower side;nbsp;the branches sent off by them higher are not so strong; the arrangementnbsp;of these principal nerves indicates that the lobing of the leaf is similar tonbsp;that of tlie preceding species.

In Fig. 9, in the right-hand upper portion of the fragment, at (a), we have apparently a portion of the original sinus and margins of the lobesnbsp;preserved, as well as a part of the right lateral main lobe. This showsnbsp;that the leaf must have been quite large. In Fig. 10, at (a), in the right-hand basal portion of the leaf, we have apparently a portion of the originalnbsp;basal margin, indicating that the lower part of the leaves was shaped likenbsp;that portion of the preceding species.

Leaf large, approximately fan-shaped, cut pretty deeply into three large lobes, the lateral ones about half-way down to the base cut on thenbsp;outer margin into a shallow, acute, tooth-like lobe, similar to those ofnbsp;Liriodendron; the middle and largest lobe not preserved, but apparentlynbsp;shaped like that of the other species of the genus�that is, it was broadlynbsp;elliptical and flared out in the middle, being narrowed to the base andnbsp;summit; separated from the main lateral lobes by a sinus tliat is turnednbsp;slightly outwards and is broadest at the bottom; the main lateral lobesnbsp;above the tooth-like lobe inequilateral, slightly convex on the upper margin, with the lower one very convex, turned upwards, and ending in a subacute tip; three principal strong nerves diverge from the base of the leaf,nbsp;one going into each principal lobe, the middle one being the strongest; thenbsp;two outer lateral primaries send ofiP on their lower side, some distance fromnbsp;and at the same height above their divergence, a strong branch that curvesnbsp;upwards to enter the lateral tooth-like lobe; the primaries send off atnbsp;points higher smaller branches nearly at I�ight angles, which curve upwardsnbsp;and branch. The lateral primaries send off on the outer side the largestnbsp;branches.

This splendid leaf differs in some respects from the previously described species of Aralioephyllum, more especially in the peculiar shapenbsp;and smaller size of the subordinate lateral lobe, but it is so close to themnbsp;in essential points that it cannot be separated and placed in a distinct

riiis, more than any other species of tlie genus, shows a markedly comprehensive character. The general shape of the leaf and the positionnbsp;of the lobes remind one strongly of Sassafras. It is also a good deal likenbsp;some species of Acer. The small outermost lobes are strikingly like those

The genus Hymencea appears to be represented by one well-characterized species, which, however, so far as seen, shows very few individuals. It should, however, be stated that most of the well-preserved species ofnbsp;angiosperms from the 72d mile-post, near Brooke, such as those of Sassafras, AralicepJiylhim, Ilymencea, Alenispermites, Uedercepliyllum, etc., are obtained from the thin -layer of well laminated clay before described. Asnbsp;nearly all these plants are found nowhere but in this layer, and as thenbsp;amount pf material obtained from it was very small, the apparent rarity ofnbsp;these fossils may result solely from this fact, and statements conceniing thenbsp;abundance of the specimens should be made with this qualification.

Upper part of the leaves not seen; towards the base they are narrowed into an elliptical shape ; leaves in pairs at the summit of the petiole; petiole very strong ; midnerves of the leaves strong and prominent; lateralnbsp;nerves not seen; leaf-substance thick; epidermis thick and glossy; thenbsp;right-hand leaf is considerably larger than the left-hand one; the midnervesnbsp;of the leaves do not run through the centers of the leaves, the outer portionnbsp;of the lamina being wider.

This plant is a good deal like Hymenma primiyenia^ Saporta, as figured by Velenovsky, but the leaves are wider at base.

This genus is formed to contain a species of comprehensive type which stands nearer to Acer tlian to any other, but still differs too much to permit

its being united with it. The generic character is the same with that of the species.

Leaves of medium size, in outline fan-shaped, at base subcordate, lamina of the leaf slightly decurrent, cut deeply into three lobes, the lateral ones slightly overlapping the middle one; the middle lobe the largest andnbsp;prolonged considerably beyond the lateral ones, broadly elliptical, muchnbsp;narrowed at the base, flared out in the middle and rounded olF to a subacute end, separated from the lateral ones by a sinus which is widest at bottom and directed outwards; lateral lobes ovate-subacute, turned upwardsnbsp;and slightly outwards; the upper margin of the lateral lobes convex andnbsp;directed outward; the outer mai�gin, in its upper portion, nearly straightnbsp;and directed towards the summit of the leaf; the primary nerves, threenbsp;in number, the middle one considerably the largest, radiating from thenbsp;base of the leaf and going one into each lobe; they send off alternatelynbsp;and obliquely branches which curve upwards; tlie lateral primaries sendnbsp;off much stronger braiiches on the lower than on the upper side, and thenbsp;basal one on each side, as in Aralicephyllum, much surpasses the others;nbsp;ultimate reticulation not seen.

This elegant leaf is a remarkably comprehensive type, combining features of Acer, Sterculia, Sassafras, and Aralia. It reminds one stronglynbsp;of AralicepJiyllum, but lacks the subordinate lateral lobes.

This genus, like most of the angiosperms of modern type, has but few specimens in the Potomac beds; possibly, as before stated, because thenbsp;strata that contain them chiefly have yielded very little material.

crenulate; leaf-substance moderately thick; nerves (primary) numerous, MON XV-21

radiating from a point considerably above the base, principal ones turned upwards, lesser ones turned outwards, and the smallest turned downwards;nbsp;primary nerves send off branches very obliquely, so that they appearnbsp;almost dichotomous; the primary reticulation, formed by branches fromnbsp;these sent off nearly at right angles, is composed of large, irregularlynbsp;shaped meshes, mostly four or five sided, made by the meeting of branchesnbsp;nearly at a right angle ; the ultimate reticulation is similar but smaller.

This fine leaf is a good deal like the living Menispernmm Canadense, but wants the acute summit of that leaf. The base of the fossil is notnbsp;shown with sufficient distinctness to make it perfectly clear whether thenbsp;leaf is peltate or not. It seems to be deeply auriculate, the auricles overlapping largely. It occurs in the same stratum with the fine specimens ofnbsp;Taxodium, Brookense, AralicBphylhm, Aceripliyllmi, Sassafras, etc.

Leaf small, orbicular in shape, subpeltate ; leaf substance very thick ; nerves very obscure and slender, only three seen, radiating from a pointnbsp;some distance above the base of the leaf

This plant looks something like a Lemna. The leaf is much smaller than that of M. Virginiensis.

I place in this genus certain fragments which apparently belonged to a large, rather coarse leaf, which has a strong likeness in its nervation tonbsp;AristolocJiia. The fragments are too imperfect to permit the shape of thenbsp;leaf to be made out, but it was apparently similar to that of some speciesnbsp;of this genus.

Shape of leaf not seen ; the leaves were apparently large and rather coarse; leaf-substance thick; petiole and primary nerves very strong and

woody; subordinate nerves strong and cord-like, ultimate reticulation strong, with the nerves prominent and thread-like; primary nerves go offnbsp;from the midnerve at an angle of about 45�, sweeping around to formnbsp;bow-shaped curves; they send off branches nearly at right angles, whichnbsp;anastomose to form irregularly shaped, strongly defined meshes filled bynbsp;an ultimate reticulation which is very distinct and prominent, formed bynbsp;nerves meeting nearly at right angles.

This plant has a nervation so prominent and well characterized that a small bit of it may be readily recognized. The fragments are so muchnbsp;broken that little idea can be gotten from them of the shape of the leaf.nbsp;They occur in the redeposited sand and clay. The fragmentary conditionnbsp;of the fossils is perhaps pai-tly due to the large size of the leaf That shownnbsp;in Fig. 3 seems to be a fragment from the central portion of the leaf. Itnbsp;may show a part of the midrib. That shown in Fig. 6 seems to come fromnbsp;the lower left-hand portion of the leaf, apparently being a portion of anbsp;basal auricle which is pressed against what seems to be a part of the petiole. Tliis part of the leaf seems to have been crushed against the petiolenbsp;so as to cause the leaf to double over on itself The great size of the petiolenbsp;and that of the primary nerve in this figure indicate that the leaf must havenbsp;been very large. Fig. 5 seems to represent a fragment of the midrib, or ofnbsp;a large primary nerve; Fig. 4 gives a fragment apparently from a basalnbsp;auricle, magnified three diameters to show the nervation.

The two species placed in this genus have the genei�al character of Iledera, but do not agree with it closely enough to unite them with thisnbsp;genus. They apparently were but slightly developed, if we may judgenbsp;from the few specimens found.

The genus may be characterized as containing leaves of rather small size, rotundate in form, with nerves radiating from the base of the leaf,nbsp;the middle one being the strongest; petioles long and moderately strong;nbsp;leaf-substance thick.

Leaf rather small, probably rotundate, with subcordate base, shape not fully shown; margins undulate to crenate; leaf-substance thick; petiolenbsp;and lower portion of the midrib comparatively strong; midnerve rapidlynbsp;diminishing above; primary nerves radiating from the top of the petiole,nbsp;the middle one the strongest; on each side of the midnerve, at its base, anbsp;strong lateral nerve goes off and proceeds obliquely upwards to near thenbsp;margin ; this sends off from its base a strong, much divided branch, whichnbsp;turns outwards and downwards; both this and the main lateral nerve fromnbsp;which it proceeds forked often, the branches flabellately diverging; reticulation not seen.

This plant is a good deal like some forms of Populophyllum., but the nervation, although different in some details from the species next to benbsp;described, is essentially the same. In this the branches go off much morenbsp;obliquely, and the basal outermost branch is proportionally much larger.nbsp;The leaf is much like some of those of Hedera Helix.

Leaf-substance thick and glossy; leaf small, with margins straight, and at intervals bending abruptly, forming right angles or larger anglesnbsp;with the former direction, the lower margin nearly at right angles with thenbsp;petiole and turning slightly downwards; shape of the lower part of thenbsp;leaf polygonal; terminal lobe incomplete, so that its shape can not be madenbsp;out; on each side of it a broad tooth or lobe like the lateral one of Lirio-dendron occurs, separated from the terminal one by a broad sinus, so thatnbsp;the upper margin of the lateral lobe has a direction nearly at right anglesnbsp;with the midrib; petiole long, rather slender, but distinct; primary nervesnbsp;radiating from the top of the petiole at the base of the leaf, in type similar tonbsp;that of Aralioephyllum. There are three primaries; the middle and principalnbsp;one proceeds to the tip of the leaf, and the two lateral ones to the lateral

lobes; these latter sending off from near their base on the outer side two strong branches, and these and the primaries higher up sending off slendernbsp;branches nearly at right angles that anastomose; reticulation not seen.

This leaf also belongs to a comprehensive type, but does not combine the features of so many different leaves as the preceding. It unites thenbsp;features of Aralicephyllum, Hedera, and Liriodendron.

This genus contains only one species, whose character, owing to the scantiness of material and the imperfection of the specimens, cannot benbsp;further characterized than as having a near affinity with Eucalyptus.

Leaves small, oblong, base and summit not seen; midnerve comparatively strong; lateral nerves very slender, crowded, going off obliquely, flexuous, and branching copiously; the ultimate branches form a closelynbsp;crowded reticulation, composed of elongate, subrhombic meshes, that standnbsp;nearly at right angles with the midrib ; all the, nerves are very slender.

Leaf small, apparently spatulate in shape, flared out a little below the middle, broad, and rounded at the summit, and gradually narrowed towardsnbsp;the base; leaf-substance very thick; midnerve quite strong; nervation notnbsp;seen.

This leaf shows no characters that can serve to place it in any particular genus.

LIST OP POTOMAC FOSSIL PLANTS.

THE POTOMAC OE YOUNGEE MESOZOIC FLOEA.

Of these plants a considerable number may be omitted in any comparison with other floras, since they do not present any features that can aid in identiflcation. When, however, these have been omitted, there still remain many that are ivell characterized, and that are largely representednbsp;and widely diffused. These may be taken as characteristic of the flora,nbsp;and they should have more weight than any others in determining the agenbsp;of the strata which contain them.

Before the examination of the geological relations of the Potomac flora is undertaken it will be well to define in what sense the names of certain geological formations, to which frequent reference must be made, willnbsp;be taken in this memoir. The two formations which are capable of misconception are the Wealden and Neocomian. By some the Wealden formation is regarded as an independent group forming the uppermost membernbsp;of the Jurassic. Others regard it as a series of beds contemporaneous withnbsp;a portion of the lower Neocomian, formed in estuaries and marshes at thenbsp;time when a portion of tlie typical lower Neocomian, which is marine, wasnbsp;being deposited in the sea. The latter view is the one assumed in thisnbsp;memoir.

In this work the Neocomian period is taken as including the Urgonian and Aptian of D�Orbigny, the former being, when present, the middle

member and the latter the upper member of the formation. When, then, reference is made to Neocomian plants, fossils of the Wealden, Urgonian,nbsp;and Aptian groups are included and not distinguished.

In the regions containing Potomac areas the older flora which comes next to that of the Potomac beds is that described by me in Contributionsnbsp;to the Knowledge of the older Mesozoic of Virginia (Mon. U. S. Geol.nbsp;Survey No. 6). This is Rheetic in age.

In Virginia, and as far north as the Potomac beds have been traced and identified, if we except the doubtful location of the trunks of Tysonianbsp;Marylandica, no plants of any value in determining age have been found

But in New Jersey a large number of well-preserved fossil plants have been collected from the sands and clays that form the lowest member of thenbsp;Cretaceous of that State, and which are so largely worked at some localitiesnbsp;for the manufactiu'e of fire-brick and pottery. These plants form the floranbsp;which comes next above that of the lower Potomac beds, and possesses importance in determining geological relations.

The New Jersey fossils are being studied and described by Dr. Newberry. Until his conclusions are published we must wait for a final determination of their age. It may, however, be stated here that these fossils have been generally taken to be of nearly the age of those from the Dakotanbsp;group of the United States, or of the Cenomanian of Europe.

The geological relations of the plant-bearing beds of New Jersey and the upper Potomac, or mottled clay group of Maryland, have not beennbsp;determined, but, as has been stated before, these two groups will probablynbsp;prove to be of the same age. The two floras then with which that of thenbsp;lower Potomac may be compared as next preceding and following it, in thenbsp;areas where it is found, are the Rlimtic plants of Virginia and North Carolina, and the probably upper Cretaceous New Jersey flora. The comparison with these is important, as showing on the one hand survivors from thenbsp;older flora, and on the other hand precursors for the younger.

By the kindness of Dr. Newberry I have been enabled to see a large number of drawings of the New Jersey plants. They show that the floranbsp;of this formation is totally different from that of the lower Potomac. The

difference is much greater than one would expect in the fossils of two formations so near each other in geological age.

All of the numerons remarkable types so characteristic of the Potomac strata are wanting in the New Jersey Cretaceous. But besides this, in thenbsp;New Jersey beds angiosperms constitute much the greater part of the plants.nbsp;In the Potomac formation the ferns, cycads, and conifers form much thenbsp;greater element in the flora. One is induced to think that in producingnbsp;such an entire change in the vegetation some other cause besides the merenbsp;lapse of time must have acted. The alteration is mainly caused by thenbsp;very general extinction of the Jurassic types which still survived in thenbsp;Potomac flora, and of the warmth-loving plants which existed in it. Thenbsp;question might be asked, Was this change hastened by the coming on of anbsp;cold period in this region in the interval between the lower Potomac andnbsp;the New Jersey Cretaceous ?

In the description of the different species of Potomac plants attention was called in each case to the known fossils that are identical with or mostnbsp;nearly allied to the plant being described. It will perhaps be useful to repeat in this place these statements, in part at least, and to add such details asnbsp;may suggest themselves, in order that we may get a connected view of thenbsp;geological relations of the flora. For this purpose I will take up in succession the different groups of plants, and try to give what may be deducednbsp;from their character.

It might cause error to attempt to determine the age of the flora by giving percentages of the elements common to the Potomac and knownnbsp;floras. In many cases particular species are represented by few individuals, and these are not well characterized. In other cases, much fewer innbsp;number perhaps, the species may be represented by numerous individualsnbsp;which are well characterized and widely diffused. Species of the kind lastnbsp;mentioned, although much inferior in numbers to the kind first named, oughtnbsp;to have more weight than these in fixing the character and determining thenbsp;age of a flora. Then, again, some species may be merely survivors of annbsp;older flora, or newly introduced precursors or prototypes of forms thatnbsp;attain their typical character later. These are not of so much value in

fixing age as species attaining their maximum development in the age in question.

One of the most noteworthy features of the Potomac flora is the overwhelming predominance of new species and the proportionally very large number of peculiar types. It is true that, owing to the absence of the flowers and fruit, we may in many cases fail to place with accuracy the formsnbsp;in still living groups; but still, in a very large number of cases, enough isnbsp;shown in the foliage to indicate that it differs in type from that of the plantsnbsp;of other formations, and in a considerable number of instances the character is so remarkable and well defined as not to requii�e any other evidencenbsp;to prove the uniqueness of the plants possessing it.

We might explain the remarkable abundance of new forms in the Potomac by assuming, for the region and peiiod possessing this flora, unusual topographical or climatal features, but this is rendered improbable by thenbsp;fact that the flora of the formation possesses a number of species knownnbsp;from other parts of the world. When we consider the distance that separates the countries in which these common species grew their similarity isnbsp;surprising.

It is more probable that the peculiarity of the Potomac flora is to be explained by the fact that it belongs to a period whose land plants have notnbsp;been found elsewhere, or if found are poorly represented. As will be seennbsp;later, this conclusion tallies with the deductions to be drawn from an examination of the individual elements composing the flora. If, as we are led tonbsp;think from a study of the plants composing this flora, its age is Neocomian,nbsp;then we should expect to find in any lai-ge collection of its fossils a greatnbsp;proportion of new forms; for the Neocomian, taken the world over, is predominantly marine, and its land flora is one of the least known.

Taking up now the different groups composing the Potomac flora, we find the Equiseta first in order.

In passing from the flora of the Rhtetic beds of North Carolina and Virginia to that of the Potomac, we find a very marked change in thenbsp;Equisetacece. There is in the Potomac no trace of Sclmoneura, a groupnbsp;meagerly represented in the Rhsetic flora in foliage at least.

The Equiseta have undergone a significant change, assuming decidedly more recent features. The Rhmtic equiseta, although few in species, seemnbsp;to have attained a very large size and to have lived in vast numbers in certain conditions of the marshes, hardly any other fossils being found withnbsp;them. They were also apparently unbranched. In the Potomac era thenbsp;species were small in size, copiously branched, like some living kinds, andnbsp;they seemingly no longer, as in the Rhsetic, lived in such immense colonies.nbsp;It can hardly be doubted that the mode of occurrence of the specimens ofnbsp;E. Virginicwn, at the fishing hut above Dutch Dap Canal, fairly representsnbsp;its distribution in life. It seems to have grown sparingly, scattered herenbsp;and there in the midst of a vegetation consisting mainly of ferns, cycads,nbsp;and conifers, with now and then an angiosperm. At Baltimore E. Mary-landicum grew rather abundantly with similar elements, but with a predominant angiospermous flora. These two, from their comparative abundance, appear to be the most characteristic equiseta of the era. E. Lyellinbsp;is almost wholly confined to Fredericksburg, and from its rarity therenbsp;seems to be a survivor from Jurassic times. This is indicated also by itsnbsp;comparatively large size. While the general character and distribution ofnbsp;the Potomac equiseta indicate an age decidedly younger than the Rhmticnbsp;and even the Jurassic, the same result would be deduced from an examination of the two more characteristic species.

Equisetum Virginiciim is so near to E. Burchardti Dunk., that it is not entirely clear that it should be made a distinct species. At least it may benbsp;regarded as a representative of E. Burchardti in America. E. Marylandi-cuni belongs to the same type of small equiseta as E. Virginicum and E.nbsp;Burchardti, which, in its copious branching and small size, stands near tonbsp;the living species of the genus.

So far, then, as the meager evidence of the Equiseta goes, we would infer that the age of the Potomac beds is Wealden (i. e., older Neocomian)nbsp;or younger.

The evidence of the ferns, if we look to the species alone, is not clear and positive for any conclusion. A typical Mesozoic or pre-Cretaceousnbsp;flora consists almost wholly of four elements. These are ferns, cycads.

conifers, and equiseta. In such a flora generally the ferns and conifers stand first in the number of kinds and of individuals, the cycads usuallynbsp;coming next, and the equiseta last. Were it not for the considerablenbsp;angiosperm element in the Potomac flora it would be typical Mesozoic, andnbsp;this would be largely due to the great variety and the universal diffusionnbsp;of the ferns. While the number of different kinds of ferns is pi'oportionallynbsp;very large, the number of individuals of each kind is, comparativelynbsp;speaking, very small. There is also a curious mingling of older and morenbsp;recent types, and a remarkable localization of many of the species. Thenbsp;species identified with those of other floras seem to be mainly a few worldwide and long-lived forms. Many of the older types seem to be survivorsnbsp;from the Jurassic. The flora of the Cenomanian is quite well known fromnbsp;a number of widely separated regions. The fact that nearly all of thenbsp;ferns of the Potomac are absent from the different Cenomanian floras isnbsp;strong evidence that the Potomac flora is older than Cenomanian.

Let us now rapidly examine the evidence to be deduced from the different groups of ferns. Gladophlebis: The ferns placed in the genus Cla-dophlebis do not, it is true, show fructification, but the plan of their foliage and nervation is a well-marked one, which is, the world over, very characteristic of Jurassic floras. The great number of species of this type foundnbsp;in the Potomac flora is certainly significant. In no flora which does notnbsp;have strong Jurassic affinities could such a large proportion of the ferns benbsp;of this type. It would seem that the conditions prevailing in Jurassicnbsp;times favored the development of this particular kind of foliage, and wenbsp;may assume that in the Potomac era these conditions had not wholly passednbsp;away.

The presence of such a large element, having the facies of Gladophl^is, is entitled to more weight in fixing the geological relations of a flora thannbsp;the establishing of the identity or near relationship of a few species innbsp;two widely separated floras. But we are not without confirmatory evidence derived from this source. The species of this genus in the Potomacnbsp;flora are probably all new, but some of them differ so little from some ofnbsp;those occurring in the Rhsetic and Jurassic floras, that they may fairly benbsp;taken as survivors and representatives of the older species. For example,

G. constricta is very near to Aletliopteris cycadina Schenk, from the Weal-den. C. Virginiensis is perhaps not to he distinguished from Brongniart�s Pecopteris Whithiensis of the Oolite of England, and is very near to Acros-ticJiides linnceccfolius, from the Rhsetic of Virginia. C. denticulata is muchnbsp;like Neuropteris ligata, Bindley and Hutton, from the Oolite of England.nbsp;O.falcata is very similar to a large number of Jurassic ferns grouped bynbsp;some under the general name Whithiensis, being in its smaller forms especially like C. nehbensis Nathorst, from the Bhsetic of Sweden. C. pcirva isnbsp;very close to C. pseudowJiitbiensis, from the Rhsetic of Virginia. It is hardlynbsp;worth while, however, to trace further the resemblance of the species ofnbsp;Potomac Cladophlebids to those of other floras.

Pecopteris: The genus Pecopteris, taken simply as a type of foliage and nervation, has hut little value in fixing age, for this group does notnbsp;seem to he characteristic of any particular geological period. The genusnbsp;is but little developed in the Potomac, and its comparative rarity maynbsp;perhaps be taken as evidence, such as it is, of the comparatively recentnbsp;age of the beds. But in this genus we are enabled to detect two speciesnbsp;as common to the Potomac and known floras, while several are very closenbsp;to previously described plants. The identification of the Potomac fragments with Heer�s P. Sodalis, from the Atane beds or Middle Cretaceousnbsp;of Greenland, does not have much weight, as the Potomac fossils are quitenbsp;rare and imperfect. The case is different with P. Broivniana. This is annbsp;important and characteristic plant in the Wealden of Europe. It is widespread in the Potomac beds, and is largely represented by identical ornbsp;nearly allied forms, such as Pecopteris strictinervis and P. constricta, giving,nbsp;indeed, a type form. Besides these we have P. Virginiensis, much like P.nbsp;denticulata Brong., an Oolitic fossil

Sphenopteris: The genus Sphenopteris, like Pecopteris, taken simply as a type of foliage and nervation, does not characterize any particular era.nbsp;But in the Wealden everywhere there is one particular type of Sphenopterisnbsp;which is highly characteristic of that formation. This is the so-callednbsp;species Sphenopteris Mantelli. The adjective so-called is used because innbsp;my opinion too many probably different plants have been united undernbsp;this name, as has been done in the case of Pecopteris Whithiensis. As

matters now stand, Sphenopteris ManteUi is the name of a particular type of foliage and nervation very common in Wealden ferns rather thannbsp;the name of a single species. But however this may he, the evidencenbsp;given by the presence of this type of fern is not affected. The existencenbsp;in a flora of a large element in the ferns which has the type of S. ManteUinbsp;may be taken as indicating affinities with the Wealden flora.

Now in the Potomac flora not only is S. ManteUi present in beds which show plants of the most recent facies existing in the formation, butnbsp;there is a very important group of ferns which, although placed in thenbsp;genus Thyrsopteris, have nearly the nervation and foliage typified in 8.nbsp;ManteUi. The great development in the Potomac of ferns of the generalnbsp;type of 8. ManteUi gives strong evidence of Wealden or somewhat laternbsp;age. A somewhat later age than Wealden is indicated, perhaps, as most ofnbsp;the species are somewhat modified, so as to depart more or less from thenbsp;typical 8. ManteUi., and to assume the facies of Thyrsopteris. The othernbsp;species of 8phenopteris give little help in fixing the age of the Potomacnbsp;strata.

Aspidium: The genus Aspidiem would seem to be, when largely developed in a flora, a decidedly recent element. The finding of as many as fourteen species of true Aspidium in the Potomac flora, and the comparatively large number of individuals shown by some of these, would, if takennbsp;alone, indicate a very recent age for this flora.' There is nothing in thenbsp;foliation or in the fructification to make us think that these plants could notnbsp;be still living. Aspidium Oerstedi is determined as present, but the identification is doubtful, as the amount of material found is too small to permitnbsp;any sure conclusion. With the exception of A. Dunkeri Schimper, the othernbsp;species are peculiar to the Potomac formation. Pecopteris Dunkeri Schimper, of the Wealden of Europe, seems to be quite characteristic of that formation. It is pretty certainly an Aspidium, as shown by the Potomacnbsp;forms. It is a plant of considerable importance in establishing the existence of Wealden elements in the Potomac flora.

Polypodium and Acrostichum: These two living genera are probably sparingly represented in the Potomac flora. Of course, as far as their evidence goes in this flora, they establish relations with living plants rather than

with the older pre-Cretaceous floras. But their presence is not certainly-established, and, if present, their species are too few and feebly developed to indicate anything more than a recent inti'oduction.

Acrostichopteris seems to be an extinct genus, peculiar to the Potomac formation. It can then give but little aid in fixing geological age. Thenbsp;fact, however, that it is extinct probably denotes a comparatively great agenbsp;for the formation to which it is confined.

Asplenium: This genus also, if present, is probably to be considei�ed as a recent element, but newly introduced.

Thinnfeldia: This genus shows three species; one of them, Thinnfeldia variabilis, being quite common at the 72d mile-post, near Brooke. The genusnbsp;is an old one, characterizing the Ehsetic, and Infra-Lias. The continuancenbsp;of this type into the Potomac formation makes an important addition to thenbsp;older elements of the flora. The species, although not capable of identification with any of those of the older floras, must be regarded as survivors.

Stenopteris: This genus is doubtfully present. It is too rare and too imperfectly preserved to be of use if present. It is one of the still lingering Jurassic types, now almost extinct.

Angiopteridium: This is a more valuable genus in throwing light on the age of the flora containing it. The absence of fructification in thenbsp;Potomac plants, however, renders it impossible to say positively whethernbsp;or not these forms are really Angiopteridium; but it is at least clear thatnbsp;large ferns with this type of foliage are more characteristic of the oldernbsp;Mesozoic formations than of the later ones. While the number of individuals of any particular species is very small, yet the number of speciesnbsp;is surprisingly large, and the genus adds much to the archaic facies of thenbsp;flora. This is one of the groups which does not appear to go up into thenbsp;Cenomanian flora, and hence, like Cladophlebis, it must be regarded as anbsp;still surviving older element.

GleicJienia: This genus, which, as Heer has shown, is so largely represented in the older Cretaceous of the northern part of the American continent, shows a surprising deficiency in forms in the Potomac flora.

Aspleniopteris; This is an extinct form peculiar to the Potomac beds, and for that reason it can give us little help in determining the age of the

Potomac by a comparison of its plants with known floras. Its extinction indicates a considerable antiquity for the Potomac strata.

Thyrsopteris: What was said of GladopMebis may in the main be repeated for this genus. It is true that, as no fructification has been foundnbsp;on these ferns, they may be incorrectly placed in the genus Thyrsopteris.nbsp;Still, the very great development in the Potomac flora of ferns with anbsp;foliage and nervation so characteristic of the later Jurassic and Lower Cretaceous can not be without significance. This type of fern is much thenbsp;most common in the Potomac strata. The species, most of them well characterized, number forty. They are distributed over the whole of the Potomac area, and a number of them are among the most common ferns at thenbsp;localities yielding them. This group, more than any other, tends to give anbsp;Mesozoic facies to the Potomac flora. They have almost or quite passednbsp;away in the interval between the time of the deposition of the lower Potomac and that of the oldest Cretaceous of New Jersey. Their absence innbsp;the flora of the latter group greatly adds to the comparatively recentnbsp;aspect of this latter.

A number of these Thyrsopterids have the same type of foliage as the Wealden ferns, Sphenopteris Mantelli Brongn.; 8. Gmpperti Dunker; 8. corded Schenk; 8. plurinervia Heer; and 8. Gomesiana Heer, as well as thenbsp;Urgonian plants Asplenium Bichsonianmi Heer; A. NaucMiofficmuni Heer,nbsp;and various Dicksonias, such as D. Johnstrupi Heer. It is a significant factnbsp;that this type of foliage, so common towards the close of the Jurassic andnbsp;in the oldest Cretaceous, is the most abundant single type in the Potomacnbsp;strata also. Such a general prevalence of a type is more significant ofnbsp;geological relationship than the identification of a few species common tonbsp;two formations. It is not worth while to examine in detail the atfinities ofnbsp;the different species. Most of them are new and unique. One or twonbsp;have some resemblance to Oolitic species, while a greater number maynbsp;be grouped as belonging to the two Wealden types 8. Mantelli and 8nbsp;Geepperti.

Osmunda; The plants placed in the genus Osmunda, although not numerous in species, are very common at the Potomac Run locality.nbsp;They quite possibly differ somewhat from true Osmundas, the genus not

being fully differentiated. If so, this genus can not be used in determining the age of the strata. It would simply indicate for them a very considerable antiquity.

Sa(jeno])teris: This is a well-marked genus, not easily mistaken for any other, and hence it is valuable in determining age. It has such a wide rangenbsp;in time, however, that it will not enable us to fix within narrow limits thenbsp;horizon of the beds containing it. It appears to extend from the Rhseticnbsp;into the lower Cretaceous or Neocomian, surviving in the Neocomian ofnbsp;Westphalia.

Sderopteris: This genus is well characterized, so that it is readily detected. It has a considerable number of species in the Potomac beds,nbsp;although none of them are anywhere common. This group of plantsnbsp;gives to the Potomac flora one of its most important Jurassic elements, fornbsp;this type is eminently characteristic of the later Jurassic. It must benbsp;regarded as a survivor in the Potomac, coming down from an older flora.

Ctenopteris: This genus has, so far as the question of age is concerned, very nearly the same significance as Sderopteris, hemg Jurnssic. But thenbsp;Ctenopterids of the Potomac appear to be modified descendants of thenbsp;forms found in the older floras. Tliey do not necessarily imply an age asnbsp;great as even that of the Oolite, and it should be noted that some of themnbsp;much resemble Pleer�s genus Ctenidium, found in the Wealden of Portugal.nbsp;There is nothing in the general character of these Potomac plants thatnbsp;would make it improbable that they occur in the older Neocomian.

Zamiopsis: This is a remarkable type, peculiar, so far as known, to the Potomac. It can not help us in determining the question of age.nbsp;This genus appears in some points to be allied with Ctenopteris, for it hasnbsp;the same curious union of the characters of ferns and cycads.

The comparatively large number of cycads in the Potomac strata does much to separate the flora of this formation from that of the Cenomanian, and to increase in it the resemblance to the typical Mesozoic ornbsp;Jurassic flora. They indicate that in the Potomac tropical conditions stillnbsp;prevailed to a considerable extent. Cycads are rare after the Neocomian

in the fossil floras of countries now possessing a cool temperate climate. We are, then, from a consideration of the family as a whole, entitled tonbsp;hold that the Potomac flora can not he later than Neocomian in age. Thenbsp;character and the degree of development of the particular genera andnbsp;species point unmistakably to the Neocomian as the age of this formation.

Anomosamites: This is an old type, belonging to the Rhsetic and older Jurassic. Anomommites proper is but slightly developed in the flora, andnbsp;at the same time, not being clearly established by the few and imperfectnbsp;specimens found, may be passed by. The case is different, however, withnbsp;the subgenus Platypterigium. This is a well-characterized form, and thenbsp;comparatively large number of fairly well preserved specimens found atnbsp;Fredericksburg give it considerable weight. The genus seems to be mostnbsp;characteristic of the Rhmtic and older Jurassic, but it almost certainlynbsp;survives until the middle Cretaceous in Heer�s Nilssonia JoJmstrupi, fromnbsp;the Atane beds of Greenland. There is, then, nothing strange in findingnbsp;this genus in Neocomian strata.

Zamites: This is eminently a later Jurassic genus, but the Potomac specimens are too imperfect and uncertain to be used.

Encephalartopsis: This genus, from its nearness to the living Encepha-lartos, is a recent element in the flora. From its great rarity, however, it is not entitled to much weight, and must be regarded as a newly inti�oducednbsp;form.

Ctenopliyllum: This is an old type. As it is exceedingly rare and differs a good deal from the most common Rhsetic form, it must be regardednbsp;as a survivor.

Ctenis: The same may be said of this as of Ctenopliyllum. It is a considerably modified survivor from the Rhsetic and Jurassic floras.

Podosmnites: This has no value in fixing definitely the age of a flora, for, as the name has been used, it ranges throughout the Mesozoic. Innbsp;addition to this, the Potomac yields only detached and sparingly dispersednbsp;leaves.

Dioonites: This genus, known from the Neocomian (�rgonian) of the Wernsdorf strata, is entitled to great weight in fixing the age of the Potomac. It is well characterized, widely distributed, and very abundant in

the Potomac, being� one of the most characteristic plants in it. It is surprising to find such a close resemblance between the most common forms of the Potomac plant and the Wernsdorf fossil. This species is more important than a large number of vaguely defined plants.

Tysonia: The trunks of Tysonia have their nearest relations in later Jurassic and Wealden forms, and hence may well exist in a Neocomiannbsp;flora.

The conifers form much the most important and abundant element in the Potomac flora. In development they surpass all other groups. Thenbsp;proportion of conifers in the flora, taken alone, is a feature that stronglynbsp;indicates that it is Neocomian in age, for it seems that in this period thenbsp;conifers, in proportion to the otlier elements of the flora, are more abundantnbsp;than they are at any other time. The Neocomian age of these plants isnbsp;indicated also by the near affinity of many of the types to present forms, andnbsp;by the existence in it of very important and well-characterized genera thatnbsp;distinguish the Neocomian strata of various parts of the world. At the samenbsp;time, however, there are in this flora a number of unique types, that indicatenbsp;that the Potomac was a period of rapid development for the conifers, innbsp;which many genera became extinct. The existence of these and a numbernbsp;of groups which might be regarded as prototypes or ancestral forms ofnbsp;living genera shows that, notwithstanding the existence in it of a numbernbsp;of angiosperms, this is a very old flora.

Nageiopsis: This remarkable genus is greatly developed in the Potomac and highly characteristic of it. It is so much like the Nageia section of Podocarpus living in the East Indies, Java, and Japan, that it is difficult tonbsp;resist the idea that there is a genetic connection between them; Nageianbsp;being a survivor and descendant of Nageiopsis. This is confirmed by thenbsp;remarkable isolation and limited development of Nageia. It is interestingnbsp;to note the fact tliat so many of the cliaracteristic coniferous types of tlienbsp;Potomac flora have their nearest living representatives in certain genera ofnbsp;very limited development and. restricted distribution confined to the easternnbsp;coast of Asia and to xiustralia. Among these may be mentioned, in addition to Nageiopsis, Athrotaxopsis, now represented by Athrotaxis in Tas-

mania; Frenelopsis, represented by Frenela in New Holland; Cephalotax-opis by Cephelalotaxus, in China and Japan; and Baieropsis, by Ginkgo m Japan. The same is true of a number of the ferns, cycads, and protealike angiosperms.

While Nageiopsis has not been recognized outside of the Potomac formation, yet some of the species are much like fossils previously known and described under other names. There are a number of species ofnbsp;Fodosamites that resemble some of the forms of Nageiopsis, which it is notnbsp;worth while to mention. Zamites Geepperti Schenk, however, from thenbsp;Wernsdorf beds, is so much like Nageiopsis longifolia tliat it is difficult tonbsp;think that it is a different plant, while N latifolia seems to belong to thenbsp;same bi�oad-leaved coniferous type as the Podozamites Beinii of Geyler.

Feildeniopsis: This is a decidedly recent element, being near Heer�s Miocene Feildenia.

Pligllocladopsis : This might be placed with Nageiopsis, etc., among the types which are represented most nearly among living plants by restrictednbsp;genera in the Chino-Australian region, as it finds its nearest kin in Pliyllo-cladus of New Zealand, Borneo, and Tasmania. But both Feildeniopsisnbsp;and Pligllocladopsis are too rare in the Potomac flora to have much importance. So far as they go, they indicate a more recent age for the formation.

Baieropsis: This is a very important genus in the Potomac, but owing to the fact that it is a peculiar type, confined to the flora of that for-motion, it can be of little help in determining age. This is one of the mostnbsp;widely diffused and characteristic types found in the formation. The fanshaped and split-leaved Gingkos form a group eminently characteristic ofnbsp;the later Jurassic and Wealden. Possibly Baieropsis is a descendant ofnbsp;Ginkgophyllum, and if so, its presence is quite compatible with the Neoco-mian age of the flora which contains it.

Baiera: This is most characteristic of the Jurassic, but it is too spar-ingly present to have any importance.

Frenelopsis: This genus has all the characters that would give a fossil plant weight in a flora. It is well chai�acterized, well distributed, and verynbsp;abundant at some localities. F'renelopsis parceramosa is very near to thenbsp;Neocomian F. Hoheneggeri, and the genus is confined to the Wealden and

Urgonian groups. Frenelopsis ramosissima is so much like Frenela that a genetic connection can hardly be denied, and this latter would seem to benbsp;a younger form than F. parceramosa.

Brachypliyllum: The Potomac forms of Bracliypliyllum are most like Heer�s Bracliypliyllum ohesum from the Wealden of Portugal.

Leptostrohus: This is Jurassic, and lends additional weight to the older elements of the flora.

Laricopsis: This must be regarded as a recent element, but it differs from Larix enough to render it doubtful whether it could be regarded asnbsp;indicating any particular post-Jurassic time.

Torreya: This belongs to the more recent forms, but it is too slightly developed in the flora to have much weight.

Ceplialotaxopsis; This is a very important and highly characteristic plant. It is unmistakable in character, widely diffused, and I�epresented bynbsp;several species, some of which seem to have been abundant. It is so muchnbsp;like Cephalotaxus that possibly it should not be separated from it. It addsnbsp;much weight to the more recent elements of the flora.

Atlirotaxopsis: This is very near the living genus Atlirotaxis, and the same may be said of its significance that was said of Ceplialotaxopsis.

Sequoia: This is the most important genus of conifers in the Potomac formation, on account of both its large development and the number ofnbsp;species that it shows common to the Potomac and to the lower Cretaceousnbsp;floras of other parts of the world. Thus we find in the Potomac and innbsp;the Urgonian strata of Korne, Greenland, the species 8. Eeichenbaclii, S.nbsp;amhigua, S. riyida, 8. gracilis; and, in addition, the species 8. suhulata isnbsp;found in both the Potomac and the Atane, or middle Cretaceous, beds ofnbsp;Greenland. Considering the number of species, this is proportionally anbsp;large number of common ones. Sequoia gives more previously knownnbsp;species than any other genus of plants.

Araucaria: This genus begins in the Jurassic and comes down to the present time, so that the Potomac species, being peculiar to it, can notnbsp;indicate any particular post-Jurassic era.

Taxodium (Glgptostrobus): The Gl3^ptostrobus type of Taxodimn is most characteristic of the middle and upper Cretaceous; and the Potomac

species, although new, have most affinity with species from formations of those ages.

Splienolepidium: This is one of the most important coniferous genera in the Potomac, It gives two characteristic genera of the Wealden abundant in the Potomac, viz, 8. Kurrianum and 8. 8ternber(jianum. The largenbsp;development of this type adds much to the weight of evidence for thenbsp;Neocomian age of the Potomac.

Ahietites: The type of cones placed in Ahietiies is too poorly preserved and too rare to have much value; but, so far as their evidence goes, itnbsp;indicates an age more recent than the lower Cretaceous.

We may pass over the various forms of fruits and inflorescence, and of course the undetermined plants, as too poorly characterized to throw lightnbsp;on the question of age, and take up the angiosperms.

The angiosperms, in the number of kinds and in the degree of devolop-ment of some of the species, are pretty well represented. Hitherto it has proved so uniformly true that, with the single exception of Heer�s Populusnbsp;primceva from Kome, angiosperms are totally absent from all Neocomiannbsp;floras, that Saporta is inclined to think that this Populus was erroneouslynbsp;ascribed to Kome. Any considerable number of angiosperms in a floranbsp;would, perhaps by most if not all paleobotanists, be taken by itself as almost,nbsp;if not quite, proving the post-Neocomian age of the flora which contains them.

Now, for the first time, we have presented in a flora which possesses an overwhelmingly large proportion of Jurassic or typical Mesozoicnbsp;elements a very considerable number of angiosperms. The presence ofnbsp;these plants, taken by itself, should not induce any one to assume that thenbsp;Potomac flora is post-Neocomian. It simply confirms the assumptionnbsp;made by more than one writer, that the apparently sudden advent of thisnbsp;type of plants in predominating numbers in the Cenomanian is not to benbsp;taken as indicating their true mode of appearance. Perhaps all paleobotanists will admit that angiosperms really made their appearance gradually,nbsp;and that their first advent must be looked for far back in the Mesozoic, innbsp;the midst of a flora essentially Jurassic or Mesozoic in type.

The character of the Potomac angiosperms shows that the first advent of this class must be looked for still further back in time, but the Potomacnbsp;flora gives us the first appearance of this high type in any notable amounts,nbsp;and shows that these plants, at least as early as the oldest Cretaceous, werenbsp;present in considerable numbers, thus pushing back by at least one epochnbsp;the date of their considerable development. It should be noted that we donbsp;not find in them, although many of them are quite archaic in type, anynbsp;forms establishing a transition between angiosperms and the ferns or gym-nosperms.

The examination of most of the genera in this group will give us but little help in making out the precise age of the Potomac flora. Most ofnbsp;them are too poorly characterized or too remote from living genera tonbsp;make a comparative study worth much. The fact, however, that a numbernbsp;of the most peculiar forms seem to be generalized types, indicates a verynbsp;considerable antiquity for the flora.

As, however, all or very nearly all of the species of these angiosperms passed away before the advent of the flora of the New Jersey Cretaceous,nbsp;we are entitled to conclude even from this group that the Potomac flora isnbsp;older than the Cenomanian. Such genera as Acacicepliyllmn, Frotecepliyllum,nbsp;and Rogersia seem to be very archaic. The same may be said, perhaps,nbsp;of Celastrophyllum, and certainly of Ficopltylhmi. Populophyllmn, Querco-phyllum, UlmiphyUum, Saliciphyllum, JuglandipJiyllum, and Eucalyptopliyllum,nbsp;etc., are too impei'fectly characterized to be of use.

Such genera as Sassafras, Vitipliyllum, Sapinclopsis, Myrica, StercuUa, Hymencea, and Menispermites are found in the Cenomanian or have closelynbsp;allied forms in it. Vitipliyllum is very near Cissites, and Sapindopsis is verynbsp;close to Sapindus, both being genera occurring in the Cenomanian. Allnbsp;these, however, are represented in that formation by species different fromnbsp;tliose of the Potomac.

The remarkable leaves shown in Aralicephyllum, Aceriphyllum, and He-dercppliyllmn, as illustrated in H. angulatum, seem to be comprehensive types, and hence are probably old forms

Taken as a whole, then, and compared with the Cenomanian flora of the Dakota and New Jersey Ci'etacoous strata, the angiosperms of

From this brief review of the flora, we see that there is in it a very large and important element that belongs to the Jurassic or typical Mesozoic flora; a less important, but still lai�ge element, that has near relations innbsp;Cenomanian and even living forms; while the largest, most fully developed,nbsp;and characteristic element is most nearly allied to forms distinguishing thenbsp;Neocomian.

All the important species common to the Potomac and the floras of known formations are found in the Neocomian, including under this namenbsp;both the Wealden and Urgonian.

If any additional evidence were needed of the Neocomian age of the Potomac, it may be found in the peculiar union of old and new types,nbsp;whose evidence, if we consider them by themselves, is contradictory.

Schenk, in Die Foss. Pflanz. der Werns. Schichten, page 29, in speaking of the character of the Neocomian flora of the Wernsdorf beds, well says that the flora of the older Cretaceous occupies in the development ofnbsp;the plant kingdom a position similar to that of the Trias, for the formsnbsp;characteristic of two great periods of development meet in. it; that is, thenbsp;survivors of the past period (Mesozoic) and the new forms of the approaching one (Tertiarjquot;).

This being true, we should expect to find in any large collection of Neocomian plants a great mingling of types. We would find the survivorsnbsp;of the old floras and the newly arrived precursors of the more recent onesnbsp;mingled with a number that attain their development in and are peculiarnbsp;to the Neocomian. This is exactly what we find to be true of the Potomacnbsp;flora. That so many of these plants are new is perhaps to. be explained,nbsp;in part at least, by the fact already mentioned, that the flora of this epochnbsp;is very poorly represented and comparatively but little known. It is notnbsp;possible to say positively to what precise epoch of the Neocomian thenbsp;Potomac belongs. Its flora ranges from the Wealden through the Urgonian, and probably includes some Cenomanian forms.

S o o PQ lt;0 lt;D Q	�s �3 �3 (A je a o	a o rS o * � p	o agt; 3 bl 0 2 .2	d lt;D ce H JO B X	�i o 'E a	� Ph o cS s o o p 4) a lt;0 95 'd cS s	3 P tj eS s o o P ei 4) a a	4^ 03 O P4 d ca c-	o o PP Ph 4) d a ej PP	03 Vi 4 �	a rt d ? o 4gt; O	d o 3 d X rd Squot; fcX. 4 ��) H	a PP 4 93 d o W 4	d o Vd a Id 1h O ta	d o 03	4 O a P	4 � a c8 P	� P4 i a � � p d 4 d 4 quot;d bO 3	4 � 4.� 4 PP	*4 4 d � O

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B o o PQ P. lt;� Q	� �V g H	71 a c3 Q o X o S ;=)	�3 X bt a 3 X	s gt; ce rlt; Ih o 'sS a?	fei P .P X C3 O T3 43 Ch L	a amp; � 43 a B � � Pm {-gt; c3 � a � 'tn -0 o Ph	a d o C4 a � � S � PM � a � �	4^ � P. � 'a	� � � pp ei � a X p PP	V. � x	1 O' � � � O	p � X fei) � '�	5t3 3 � P O H � X	p � fei p X � �	R O fei a amp;	� o a CQ	� a p K	p P Ph � c4 a � � Ph � p � �fl feC	quot;a PP	M lo � a �
B o o PQ P. lt;� Q	� �V g H	71 a c3 Q o X o S ;=)	�3 X bt a 3 X	s gt; ce rlt; Ih o 'sS a?	fei P .P X C3 O T3 43 Ch L		a d o C4 a � � S � PM � a � �	4^ � P. � 'a	� � � pp ei � a X p PP	V. � x	1 O' � � � O	p � X fei) � '�	5t3 3 � P O H � X	p � fei p X � �	R O fei a amp;	� o a CQ	� a p K		quot;a PP	M lo � a �
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a o � p:) � � P	gt;4 � a � u H	� � a. quot;o P	V � JS, bJC .a * 1	S � n � 3 'J1	u s ,�gt; � '5 � 'C � k. tR 1 1	d p � a o � p u a � a � in '� e� C P5	d 0 � a � o p CQ � a � *� s	o (?. � a �1 1	� � o � p � a a p	V; � 3 M	d �5 � � o	p S quot;3 (/I i- sc � '�	P � to 5 W � 13	d o bC P 5 m 6 o P	o 4.� .a cc	� O a quot;3 P	u � o p e� P	d P P � cS a � � p u cS � p � a tt. P	'gt; m s P	� P � �
			V � JS, bJC .a * 1	S � n � 3 'J1	u s ,�gt; � '5 � 'C � k. tR 1 1			o (?. � a �1 1
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					1

TABLES.

Table I.�List of species of the Potomac formation, with the localities at which they were collected�Cont�d.

THE POTOMAC OR YOUNGER MESOZOIC FLORA.

Table I.�List of species of the Potomac formation, with the localities at tchich they were collected�Coated.

								P	P				j
Names of the species.	agt; bC Ph	� o o � Cl. ID Oil P	.a cs di rxi 3 P H	6 p	c di � .5 a 2 �	a t* H o �s CO	p a� 2 'Z quot;p di 'A	P 9 a a o � P t. cS P � 'P cS �	P o 3S a � � p Sh cS � a � y s	3 aa � ft � a �p	� � � !-l P eS � a M a cS P	gt;! � i	a P pquot; � � � O	n � P a 3. eS h 0(1 � H	5� P P � P � w �	p � U p 2 eS � P	P o S) p 2 as P	� � a 2 p p	� � p cs w	5 P o cs a p � p b. cS � P � 2 bC 2	� os 2 P	j6 '� � P � �
	210				1
	210				1						1
	210													1
	211						1							1
	212						1
	212						1
	213				1
	215						1
	218		1
	221		1		1
	223													1
	223		1
	224		1
	224		1
	228				1		1		1		1
Leptostrohus foliosus, n. sp.....................	230			1	1											...				....
	230
	231				1
	231				1
	232
	233				1
	233		1		1
	234		1
	234		1							1
	235								1
	236				1		1
	237						1	1
	238						1
	238				1		1
	240
	241				1
	241		1	1	1				1
	242			1	1				1
	243			1
Sequoia Keicheubaehi (Gein.) Heer.............	243			1	1
S. lleicbenbachi longifolta, ii, v..................	244			1	1		1
Sequoia subulata Heer..........................	245				1		1							1
	245				1
	246								1					1
	246				1
	247									1	1
	247				1
	247						1
	248						1			1
	248						1
	249									1
Araucaria obtusifolia, n. sp.....................	249	..il

a � � PQ Plt; � a	i � � K � (h H	a �3 di a -a � 4.3 d	c a A ttO p i ?	g � H 5-1 � 02	bi) a -p ao � � na � M	a ' 1 C3 a � � � a � CD '� M	a a � a zgt; 0 � �	� � � a -o	� � � � � a a n	os V. � M 0	0 �� a O� � � � O	0 � � IS H	a w � a � � A	0 O bC a 2 Ch O	0 B b� 0 B �	� s-gt; � a 43 ' M	� O 0 tS W	a a � ci a � O Pm U � 0 � 4^ *a bc 3	� � �� SP	lt;a '� � 0 � �
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			1
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THE POTOMAC OR YOUNGER MESOZOIC FLORA.

Table I.�List of species of the Potomac formation, with the localities at which they were collected�Cont�d.

a s o C� 3 o o p.. cs 0) a � '3 '6 ei M	a p � d S � 5 a. � rt a �o * 5	o amp; 3 �M	6 o o M a � a M a d �	�� ^6 a d w	a a 1 � o	a .2 d aa A � Sc � '�	s o � 2	a o bt) a 2 o ft,	a o bi a 2'j � 1 d	� a 1	� � a C! s	a* a a � � Ph a � a � a bt 3	� gt; quot;�	aO � � a �
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1
1		1

TABLES.

Table I.�List of species of the Potomac formation, with the localities at which they tvere collected�ContM.

a o 0 Pi' ngt;	� 0) 3h a H	as � o �� ti .a � S fi	6 fcr c a;	a V H 1- o � 02	bl � 45 CC o flj quot;O p	� o a o � d � 3 x '� o	a o d a � � � a � X 3	X c Ph � a 'C t-	� o � u � d eS w	X �� d (�	cS d U' � � � O	d _� Te 55 45 Pi � fcX � � H	5� s s � � o w �. 2	B � quot;Sj d 2 X �	d O X rt	� � a Ts W J	� � gt; � a as w	d s Pi � d a � � Ph � a] � d _� quot;d fct	� gt; X 4* *� PP	X '� d d � o
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Cretaceous.

Neocomian.

Urgonian.

Gault.

Cenoma

nian.

kota.

Senonian.

Lara

mie.

�

3 . .d.a

� b-

pq ^ ^ �

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lt;�

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Species with which compared.

Equisetum Burchardti(Duuk.) Schimp. Identical............................

Alethopteris cycadina Schenk.

Pecopteris borealis Brgt.......

Pecopteris liberata Heer.......

Pecopteris haiburnensis L. amp; H . Nenropteris undulata L. amp; H____

Pecopteris Wbitbiensis Brgt.....

Pecopteris tenuis Schouw........

Acrostichides linnaBsefolius Bunb. Acrostichides rhombifolius Font.

Neuropteris ligata L. amp; H... Pecopteris deuticulata Heer.

Pecopteris dentata L. amp; H.............

Cladophlebis pseudowhLtbiensis Font..

Neuropteris Albertsii Hunk � Alethopteris Albertsii Schenk.nbsp;Pteris Albertsii Heer..........

Pecopteris denticulata Brgt. Pteris frigida Heer..........

Pecopteris Browniana Dunk . Pecopteris Browniana Dunk .

Identical.....................

Identical .....................

Triassic.

Jurassic.

lt;o .0 a E3 a a lt;u 00 cc	Species.	bO A Ph	Rhtetic.			Ivhse- tic 01 Lias.	Lias. d � c� C3 0 be Is .d eS a .5 a M	Oolite.							Coral- lian.		Kim- merid gian. �quot; �i a � .9 0 � a � � d d	Wealden.
lt;o .0 a E3 a a lt;u 00 cc	Species.	bO A Ph	.9 'o eS � A �s � A � c8 fl �So u F	� � cC 'S 0 � a gt;gt; a Ed 9 �	a � lt;0 cc	cd Q S �	Lias. d � c� C3 0 be Is .d eS a .5 a M	� � �quot; S-( 0 w a 85 'So d W	gt;gt; M	� *� to d	9� si a � rd 0 cq � plt; d 0 fl � be � .0 %	.d 'E � iK � cS	� � d 0 h bt 5h ft 9 .0 a .9 s H	a si ft si	9 s OQ � gt; � � d d	9 lt;4H 0 JS � 9 .9 'C c3 t- C� pq	Kim- merid gian. �quot; �i a � .9 0 � a � � d d	� d � .0 d.d bl� a'^ 'P � 90 a � 9'd 9 -9'd sh	a S-I � 0 quot;A	9 a 9 95 d
1	Equisetum Virginicum, n. sp..........	63
2	Equisetum Lyelli Mant...............	65
4	Cladophlebis constricta, n. sp..........	68

											1
5		69						1
								1
6		70						1
								1
			1
			1
7	Cladophlebis denticulata, n. sp.........	71						1

8	Cladophlebis falcata, n. sp..............	72		1		1		1
								1			1
								1
										1		1
											....
													1
9	Cladophlebis parva, n. sp...............	73						1
			1
10	Cladophlebis acuta, n. sp...............	74


11	Cladophlebis oblongifolia, n. sp........	74		1		1		1
12	Cladophlebis crenata, n. sp.............	75
										1
14	Cladophlebis inclinata, n. sp............	77
17	Cladophlebis alata, n. sp................	77
20	Cladophlebis sphenopteroides, n. sp____	79										1
23	Cladophlebis brevipennis, n. sp.........	81
25	Cladonhlebis nachvnhvlla. n. sn.......	80						1
26	Pecopteris Virginiensis, n. sp..........	82						1

27		84
30	Pecopteris constricta, n. sp.............	85
32	Pecopteris socialis Heer...............	87
34	Pecopteris Browniana Dunk...........	88																		-

Cretaceous.

Neocomian.

TJrgonian.

Gault.

Cenoma

nian.

kota.

Senonian.

Lara

mie.

�

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Species with, which compared.

Equisetum Burchardti(Dnuk.) Schimp. Identical...............................

Alethopteris cycadina Schenk.

Fecopteris borealis Brgt.......

Pecopteris liberata Heer.......

Fecopteris haiburnensis L. amp; H.......

Neuropteria undulata L. amp;. H..........

Fecopteris Whitbiensis Brgt.....

Fecopteris tenuis Schouw........

Acrostichides linnaia3folius Bunb. Acrostichides rhombifolius Font.

Neuropteria ligata L. amp; H... Pecopteris deuticulata Heer.

Pecopteris dentata L. Sc H.............

Cladophlebis pseudowhitbiensis Font..

Neuropteria Albertsii Dunk � Alethopteris Albertsii Schenk.nbsp;Pteris Albertsii Heer..........

Pecopteris denticulata Brgt. Pteris frigida Heer..........

Pecopteris Browniana Dunk..........i 27

Pecopteris Browniana Dunk.......... 30

Identical.............................. 32

Identical.............................. 341

Triassic.

Jurassic.

lt;Igt; a E3 d o d � m	Species.	bC 03 Ph	Rhsetic.			Rhse-tic 01 Lias.	Lias.	Oolite.							Coral- lian.		Kim- merid gian. � a a (h '� ^ � � a � � d ei fa	Wealden.
lt;Igt; a E3 d o d � m	Species.	bC 03 Ph	quot;o u cS � A 0 d CQ .s is �S3d F	(D *3 � d �e fa i g 0 0	g 'd �	e� d	u � fa d 0 �.i br *3 3 e? fa .�8 d M	d � �quot; A A !h 0 b. nd d e3 'fell d fa	H	.2 09 a fa	'a a a � A 0 fa � fa eS 0 d � tf} � .0 �fa CO	e� �E � A � lt;E a fa	� � fa a � h br u fa Is as a 13, .3 '5 a H	a eS fa	A 3 4i3 CO dquot; a �a (-1 � gt; � � d ei (-1 fa	1 � A d � quot;o .2 �E a gt; a fa		.a'a � d � c8 42 a43 bife I'S *0 � ��SS fa	a � 1	.s' a C8 05 8 �
1	Equisetum Virginicum, n. sp..........	63
2	Equisetum Lyelli Mant...............	65
4	Cladophlebis constricta, n. sp..........	68																	1
																			1
											1
5	Cladophlebis latifolia, n. sp.............	69						1
	Cladophlebis latifolia, n. sp.............							1
6		70						1
								1
			1
			1
7	Cladophlebis denticulata, n. sp.........	71						1

8	Cladophlebis falcata, n. sp..............	72		1		1		1
								1
								1
										1

											....		X
9	Cladophlebis parva, n. sp................	73						1		..
			1
10	Cladophlebis acuta, n. sp...............	74


11	Cladophlebis oblongifolia, n. sp........	74		1		1		1												1
12	Cladophlebis crenata, n. sp.............	75
										1
14	Cladophlebis inclinata, n. sp............	77
17	Cladophlebis alata, n. sp................	77												1
20	Cladophlebis sphenopteroides, n. sp____	79										1
2.3	Cladophlebis brevipennis, n. sp.........	81
25	Cladophlebis pachvphvlla. n. sp.......	80						1
26		82						1

27		84
30		85												.
32		87
34	Pecopteris Browniana Dunk...........	88

FORMATIONS IN WHICH THE SPECIES COMPARED OCCUR.

ti, D ft=gt; a a a o tt a D 3 02	Species.	�	Triassic. Ehaetic.			tic or Lias.	Lias.	Jurassic. Oolite.							Coral- lian.		Kim- merid gian. � 3 a �aJ ^ Is � � a � � p cS	Creta ceous. Wealden.
ti, D ft=gt; a a a o tt a D 3 02	Species.	�	e� a 'o o .�3 !-l O a C3 2 '3 'Sc	� � cf '3 o V p cS P cS a � o	p	d P 13 o	� pi p o *3 A �1 n S '5 p M	V � i3 cc o fc P eS 'tl P	gt;	03	'p' � a � .p o � CS � P � fc� (h .o '3. c/2	� ijo p � es	� � A P O b bC 3 *3 .p cS .3 Q M	P a ct	ip � d P � gt; � � p	'p � o p � o .5 M	Kim- merid gian. � 3 a �aJ ^ Is � � a � � p cS	id'pi o Pnbsp;� eS rs P o � � _p_� . ..h-5 a �o �nbsp;P	P ei a � 1	B 3 �
36	Sphenopteris thyrsopteroides, n. sp.....	89						1
								1
39	Sphenopteris Mantelli Brgt............	91
42	Aspidium Predericksburgense, n. sp____	94
44	Aspidium beteropbyllum, n. sp.......	96
46	Aspidium angustipinnatum, n. sp.....	98
48	Aspidium Oerstedi (?) Heer............	99
52	Aspidium Diinkeri Schimp............	101
53	Aspidium dentatum, n. sp.............	102						1
56	Polypodium fadyenioides, n. sp.......	104
64	Asplenium dubiuro,n. sp...............	109
												1
65	Thinnfeldia variabilis, n. sp...........	110		1
69	Angiopteridium auriculatum, n. sp.....	113
							1
70	Angiopteridium nervosum, n. sp......	114			1			1
	Angiopteridium nervosum, n. sp......						1
				1
				1
71	Angiopteridium ellipticura, n. sp.......	114					1
74	Angiopteridium ovatum, n. sp..........	115					1
75	Angiopteridium strictinerve, n. sp......	116		1
78	Gleichenia Nordenskioldi (?) Heer .	119
79	Undetermined fern.................	119
82	Thyrsopteris Virginica, n. sp........	120
												1
83	Thyrsopteris brevifolia, n. sp...........	121						1
								1
8^	Thyrsopteris dentata, n. sp.............	121						1
85	Thyrsonteris nervosa, n. sp.............	122										1
86	Thyrsopteris rariuervis, n. sp..........	123

														1						..

Cretaceous.

Neocomiaii.

Urgonian

Gault.

�

A .

P -z-

o.a

'''.p

�

p �

�

bJO

�

�3-

Cenoma

nian.

kota.

�

�3

Senonian.

Lara

mie.

�

quot;p

amp;Q

�

�3

�

-P

'bl

A .

� u

� ^

� � 3 ^

�

quot;3

�

tJC

�

.rt

�

quot;p

�

quot;o'

�

�= �

��

�

pquot;

:�

�

s�

�

quot;c

�

f-l

S P

�S'�

�o

'-S

� -g

�

quot;�

�

quot;c

Species with which compare^!.

Spheuopteris Williamsonis Spbenopteris denticulata Brgt...

Neiiropteris Albertsii Dunk. Aspleiiium argutulum Heer .

Thinnfeldia rhomboidalis Ett.

Pteris longipennis Heer......

Pecopteris salicifolia O. amp; M .

Tscniopteris vittata Brgt............

Angiopteridium McClellandi (0. lt;fcM.) Schimp.

Tainiopteris stenoneura Schenk......

Tscniopteris teiiuinervis Brauns......

Angiopteridium ense (Oldh.) Schimp.. Macrotseniopteris ovata Schimp----

Oleandridium tenuinerve (Brauns) Schimp.

Identical..............................

Aspleniuni Dicksonianum Heer.......

Dicksonia Johnstrupi Heer----

Adiantites Nympharum Heer .

Spheno})teris dissocialis Phill........

Sphenopteris hymenophylloides Brgt..

Sphenopteris affinis Phill.............

Thyrsopteris prisca (Eichw.) Heer----

Sphenoptei'is longifolia Dunk ... Asplenium Dicksonianum Heer .nbsp;Thyrsopteris elongata Geyl.....

					FORMATIONS IN WHICH						THE	SPECIES COMPAUED OCCUR.														FORMATIONS IN WHICH				THE SPECIES COMPARED OCCUR.
			Triassic.							Jurassic.								Creta ceous.					Cretaceous.
			Khajtic.			lllue-tic or Lias.	Lias.			Oolite.					Coral- lian.		Kim- merid gian.	Wealden.					Neocomian.				Urgonian		Gault.	Cenoma nian.				Da kota.	Senonian.						Lara mie.	P � � o
im V a s PI o a (D cc	Species.	o be e� P-	_g 'o i-i o a C5 d 'S 'Sc i-	� �s' '3 o � P � P CS a Ol e	P	�3 .9	�Si g te 'd d �1 d t� 9 w	o 3 fK r?5 O h P d 'bl P w	gt; M	*05 05 P	o' CS 9 -�2 O lt;s csquot; O P o b� o 'P. CO	.P a � 05 W	O -4.i � P. 3 O u be b � rP �3 -9 �s	c quot;9	*� S 3 fl� 1 ' b i � � y : P	'p �2 o pj p 'o �9 'S d 'd	.9 � � � � a s	J^rs O P � cs .p t 3 � quot;u 05 PJi . -M a *� csnbsp;9 05��2 a-pp^	p 1 �	s .9			quot;�5 o . 95 PiS ss 25 E � o ^ 05 � � �3 O o M	bt (-1 o 24	� 05 P d ja bC .9 o .2 quot;cS PS Pi 05 �	S o S-i quot;o pH � p � bt o � � p k Eh	9 o W p d 'p �	�44 o ^3 P t-i t d *� 2 ^ � I u 44) 05 s lt;1	4^� cS t4 m � Pi . 0.9 '^PS o p � � b� fc* � PS lA �9. c/2	1 s ^3 1 � � 5	� cs' P :0 -P � � �P � � o x cS cc	eS gt; d u o 3 d d a � P5	9 *c .P c c pp o � M	05 � th � p	Hi O ^-P '�'� �o 5.2 H. '-S �-c 55 pq ,P '�nbsp;* �nbsp;n P5	4i o o ns P � quot;p � � Hi O	� p- d PS � .2	9 p XI A d �	bX Hi X � O'	quot;p CS 05 O O 'c h�	cS �P d P cs � 'P p cS 05 � quot;cS � �P 0	o p � p Hi P o M '� p es 'bt P
36	Sphenopteris thyrsopteroides, n. sp.....	89						1
								1
39	Sphenopteris Mantelli Brgt............	91												1				1						1									j
42	Aspidium Eredericksburgense, n. sp....	94																1												1
44	Aspidium beterophyllum, n. sp.......	96																												1
46	Aspidium angustipinnatum, n. sp.....	98																												1
48	Aspidium Oerstedi (?) Heer............	99																												%
52	Aspidium Dunkeri Schimp.............	101
53	Aspidium dentatnm, n. sp.............	102						1				1
56	Polypodium fadyenioides, n. sp.......	104										1									.						1
64	Aspleniuni dubiuro,n. sp............	109
												1
65	Thinnfeldia variabilia, n. sp............	110		1
69	Angiopteridium auriculatura, n. sp.....	113																												1
							1
70	Angiopteridium nervosum, n. sp......	114			1			1
	Angiopteridium nervosum, n. sp......						1
				1
				1
71	Angiopteridium ellipticura, n. sp____	114					1
74	Angiopteridium ovatum, n. sp.......	115					1																																	j
75	Angiopteridium strictinerve, n. sp......	116		1
78	Gleiclienia Nordenskioldi (?) Heer____	119				�																�					?							?
79	Undetermined fern..................	119																																?
82	Thyrsopteris Yirginica, n. sp...........	120																									1
												1															1
83	Thyrsopteris brevifolia, n. sp...........	121						1
								1
8^	Thyrsopteris dentata, n. sp.............	121						1
85	Thyrsonteris nervosa, n. sp.............	122										1									1
86	Thyrsopteris rarinervis, n. sp..........	123
																											1
														1

Species with which compared.

SphenoiiterisWilliamsonis Brgt. Sphenopteris denticulata Brgt. - -

Identical..............................

Aspidium Oerstedi Heer..............

Aspidinm Jenseni Heer..............

Identical.............................

Thyrsopteris Murray ana (Brgt.) Heer Nathorstia angustifolia Heer.........

Nenropteris Albertsii Dunk. Aspleniuni argutulum Heer .

Thinnfeldia rhomboidalis Ett.

Pteris longjpennis Heer......

Pecopteris salicifolia �. amp; M .

Angiopteridium eose (Oldh.) Schimp. Macrotseniopteris ovata Schimp......

Dicksonia Jobnstrupi Heer----

Adiantites Nympharum Heer .

Tajniopteris vitiata Brgt-..-........

Angiopteridium McClellandi{0. amp; M.) Schimp.

Tmniopteris stenoneura Schenk.......

Ta�niopteris tenuinervia Brauns.......

Oleandridium tenuinerve (Brauns) Schimp.

Identical........................

Aspleniuni Dicksonianum Heer .

Sphenopteris dissocialia Pbill.........

Sphenopteris hymenophylloides Brgt..

Sphenopteris atBnis Phill.............

Thyrsopteris prisca (Eichw.) Heer____

Sphenoptei'is longifolia Dunk ... Asplenium Dicksonianum Heer .nbsp;Thyrsopteris elongata Geyl.....

FORMATIONS IN WHICH THE SPECIES COMPARED OCCUR.

Ol A B � fl o cS a lt;D ra gt;i OJ	Species.	9 tc ei	Triassic.			Jurassic.												Creta ceous.
			Phaitic.			Rhse-tic or Lias.	Lias.	Oolite.							Coral- lian.		Kim- merid gian.	Wealden.
			.9 o 5 o 'a '3 gt;	o to '3 � a ei S- d ed a 9 o	d � 'O � CC	d 3	ei � amp; 0 o a 3 .2	� 9 9 2 90 �2 O �o d '3c ?		d d	'a a a 9 rd o PQ 9 o a 9 blJ � �ft	d � .o d � (C m	9 9 d o � d A .� eS �- d IH	a �8 d. lt;8	'� S S d' d rs gt; 9 � d � �	1 �H o JS d � '� PP	9 3 a ft � .3 a � � d pcj	9 ^ 9 c3 .� dS tiS a 'P *� to d^' . 9 .2,'9 S?	cP- 5 i � j= � ;z;	.quot;s' � .2 a d 2
93	ThYrsopteria insignia, n. sp.............	127
95	Thyrsopteris densifolia, n. sp...........	129
116	Thyrsopteris heterophylla, n. sp........	142										1
125	Sagenopteris latifolia, n. sp............	148	1	1	1
126	Sagenopteris elliptica, n. sp............	149						1
				1
128	Scleropteris elliptica, n. sp.............	151						1
130		152									1
134	Cteuopteris integrifolia, n. sp........	158							1
141	Zamiopsis laciniata, n. sp...........	164															1
145	Platypterigium densinerve, n. sp......	169	1														1

				1
							1
153	Ctenophyllum latifolinm.n. sp.......	175	1
154	Grlossozaniites distans, n. sp.........	176
155	Ctenis imbricata, n. sp..................	176						1
					1
156	Podozamites subfalcatus, n. sp.........	179


160	Podozamites acutifolius, n. sp..........	181				1	1	1			1	1	1	1
			1			1
161	Dioonitea Buchianns Schimp.........	182																	1
163	Dioonites Buchianns Schimp., var. an-	185																	1
	gustifolins Font.
164	Tysonia Marrlandica, n. sp.............	193
165	Nageiopsis longifolia, n. sp.............	195																1
169	Nageiopsis latifolia, n. sp...............	198
181	Baieropsis expanse, n. sp...............	207
193	Frenelopsis parceramosa, n. sp.........	218
194	Brachyphyllum crassicaule, n. sp ......	221										1
															1

FORMATIONS IN WHICH THE SPECIES COMPARED OCCUR.

Species with which compared.

Cretaceous.

�

�d

�8

�bJD

Neocomian.

Urgonian.

Gault.

Cenoma

nian.

kota.

Senonian.

Lara

mie.

lt;8

�

�d

�5

�

quot;A .

a .2 c

S'E

�

�.H

�4^

� �

�

quot;d

�

dquot;

�

�quot;

*�

�

��

�

c3 'T

.2 � w

��

quot;S

�

O a '~'!3nbsp;� .nbsp;d �

�

fcC

�

44)

�9

�

�5

'�

-d

�

gt;;

�

�8

�

�d

�5

�

'�

.fl

�

�H

�

44)

(/2

�

H�

� � �o

�5.2

� 44� � �

*�'d � d

��

44)

�

'�

�

Pachypteris lanceolata (Phill.) Brgt...

Macrotseniopteris magnifolia (Rogers) Schimp.

Giossozamites Zitteli (Schenk) Schimp.

Zamites nervosus Schenk.............

Podozamites lanceolatus (L. amp;. H.) Brgt.

Identical (Pterophyllum abietinum Gopp. and Dioonites abietinus Miquel.

Frenelopsis Hoheneggeri (Ett.) Sebenk

Brachyphyllum Moreauanum Brgt----

					FORMATIONS IN			WHICH THE SPECIES COMPARED OCCUR.
			Triassic.			Jurassic.												Creta ceous.
			Rhffitic.			Rhie-tic or Lias.	Lias,	Oolite.							Coral- lian.		Kim- merid gian.	Wealden,
o a 3 a o cl a 9 % m	Species.	(D fee 3 ch	C� .9 quot;o U c8 � o .3 e3 .2 '3 �amp; p	d � e� '3 � � sa eS gt;5 d a 9 O	P � 'O lt;D cc	C5 a 3 u	d � amp; � Wi .a cS a c? s p H	d � � � 2 so �g � d �5 P W	Ts	e� 1 d PI	�d� c3 a � o pp � o d � fcfl � � tS9 ft cc	e� � .� cZ d � CO e� H	d � ft d � p d A 3 �S 2 d w	d p ft p	2 2 s d' d rp � gt; � � d es Em	1 �HI � .a d � 2 .a d PP	� 3 a Em � d � -H� g�- a � � d S	JaJ'd � dnbsp;� � 32 d \|o quot;� � -	5 S � Zb �	� p s 2
93	Thyrsopteris insignis, n. sp.............	127
95	Thyrsopteris densifolia, n. sp...........	129
116	Thyrsopteris heterophylla, n. sp........	142										1
125	Sagenopteris latifolia, n. sp............	148	1	1	1
126	Sagenopteris elliptica, n. sp............	149						1
				1
128	Scleropteris elliptica, n. sp.............	151						1
130	Scleropteris Virginica, n. sp............	152									1
134	Ctenopteris integrifolia, n. sp........	158							1
141	Zamiopsis laciniata, n. sp ............	164															1
145	Platypterigium densinerve, n. sp......	169	1														1

				1	1		'quot;'i'								....		......	......
153	Ctenophyllum latifoliiim, n. sp.......	175	1
154	Glossozamites distans, n. sp.........	176
155	Ctenis imbricata, n. sp..................	176						1
					1
156	Podozamites subfalcatus, n. sp.........	179


160	Podozamites acutifolius, n. sp..........	181				1	1	1			1	1	1	1
			1			1
161	Dioonites Buchianns Schimp.........	182																	1
163	Dioonites Buchianus Schimp., var. an-	185																	1
	gustifolius Font.
164	Tysonia Marylandica, n. sp.............	193																1
																		1
165	Nageiopsis longifolia, n. sp.............	195
169	Nageiopsis latifolia, n. sp...............	198												1
181	Baieropsis expansa, n. sp...............	207												1
193	Frenelopsis pavceramosa, n. sp.........	218
194	Brachyphyllum crassicaule, n. sp......	221										1
	j						......1....								1

Cretaceous.

Neocomian.

Drgonian.

Gault.

Cenoma

nian.

kota.

Senonian.

Lara

mie.

�

� q �

2�C

3p t: �

�4a

� � as

�

�d

�

quot;o

�

amp;

�

�Hlt;

�

2 � m

�

ft .

�.2

o d �

�

fcC

�

'�

�

:�

�

e�

�

�H

�

-Hgt;

(fX

�

amp;

�

4.3 .

r; d

s| � �

.c *

o'i

�W

OD P

�

1 �nbsp;O

2 Eh

e�

�

........

......

Species witli which compared.

Aspleniiim Johnstrupi Heer... Sphenopteris Gcepperti Dunk.nbsp;Thyrsopteris Maakiana Heer..nbsp;Sagenopteris rhoifolia Presl...

Glossopteris Phillipsii Brgt. Sagenopteris rhoifolia Presl.

Pachypteris lanceolata (Phill.) Brgt...

Soleropteris Pomelii Sap...............

Dichopteris Visianica Zigno...........

Stenopteris desmomera Sap...........

Macrotfeniopteris magnifolia (Rogers) Schimp.

Nilssonia Johnstrupi Heer...........

Pterophyllum Braunsii Schenk......

Pterophyllum princeps O. amp; M.......

Ctenophyllum grandifolium Font----

Glossozamites Zitteli (Schenk) Schimp

Ctenis- falcata Lind. amp; Hut. Ctenis fallax Nath..........

Zamites ovatus (L. amp;. H.) Mor.

Zamites affinis Schenk.........

Zamites nervosus Schenk.....

Podozamites lanceolatus (L. amp; H.) Brgt.

Podozamites Emmonsii Newb.........

Identical..............................

Identical (Pterophyllum ahietinum G�pp. and Dioonites abietinus Miquel

Bennettites. Mantellia...

bigt; t-s w ts

Systematic number.

�^

amp;�

�

agt;

*�

lt;

�S.

S�

�

�quot;

lt;

ft�

�

tgt; nbsp;nbsp;nbsp;73

5 nbsp;nbsp;nbsp;� 5nbsp;nbsp;nbsp;nbsp;C 5

2; nbsp;nbsp;nbsp;- Snbsp;nbsp;nbsp;nbsp;S 0

Cf- nbsp;nbsp;nbsp;s �nbsp;nbsp;nbsp;nbsp;s 0

g nbsp;nbsp;nbsp;r�nbsp;nbsp;nbsp;nbsp;r�

5 nbsp;nbsp;nbsp;wg

i � nbsp;nbsp;nbsp;� 2

� nbsp;nbsp;nbsp;2nbsp;nbsp;nbsp;nbsp;s

i p

gt;3 nbsp;nbsp;nbsp;a 72nbsp;nbsp;nbsp;nbsp;M

S nbsp;nbsp;nbsp;X ^nbsp;nbsp;nbsp;nbsp;(Tt-

O! nbsp;nbsp;nbsp;Cquot; �nbsp;nbsp;nbsp;nbsp;�

� nbsp;nbsp;nbsp;B �nbsp;nbsp;nbsp;nbsp;3

r nbsp;nbsp;nbsp;-nbsp;nbsp;nbsp;nbsp;3

�d nbsp;nbsp;nbsp;�quot;lt;5nbsp;nbsp;nbsp;nbsp;�

. nbsp;nbsp;nbsp;K-jnbsp;nbsp;nbsp;nbsp;a

; nbsp;nbsp;nbsp;3^nbsp;nbsp;nbsp;nbsp;^

: nbsp;nbsp;nbsp;pnbsp;nbsp;nbsp;nbsp;p

.30 nbsp;nbsp;nbsp;S

I nbsp;nbsp;nbsp;*1 3nbsp;nbsp;nbsp;nbsp;P

: nbsp;nbsp;nbsp;S? 3nbsp;nbsp;nbsp;nbsp;3

�

p�

�

73 nbsp;nbsp;nbsp;73nbsp;nbsp;nbsp;nbsp;72

d nbsp;nbsp;nbsp;dnbsp;nbsp;nbsp;nbsp;d

P- nbsp;nbsp;nbsp;3-nbsp;nbsp;nbsp;nbsp;�

B nbsp;nbsp;nbsp;3nbsp;nbsp;nbsp;nbsp;a

�00^

0 nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;�

d nbsp;nbsp;nbsp;d,nbsp;nbsp;nbsp;nbsp;d_

S* nbsp;nbsp;nbsp;pnbsp;nbsp;nbsp;nbsp;2�

2 nbsp;nbsp;nbsp;2nbsp;nbsp;nbsp;nbsp;2

lt;J nbsp;nbsp;nbsp;*3nbsp;nbsp;nbsp;nbsp;d

a nbsp;nbsp;nbsp;ftnbsp;nbsp;nbsp;nbsp;a

jq nbsp;nbsp;nbsp;crnbsp;nbsp;nbsp;nbsp;�

3* nbsp;nbsp;nbsp;'-5nbsp;nbsp;nbsp;nbsp;2

2. nbsp;nbsp;nbsp;dnbsp;nbsp;nbsp;nbsp;p

2 nbsp;nbsp;nbsp;5quot;nbsp;nbsp;nbsp;nbsp;3

lei

3 nbsp;nbsp;nbsp;Inbsp;nbsp;nbsp;nbsp;3

� nbsp;nbsp;nbsp;'llnbsp;nbsp;nbsp;nbsp;1

3 nbsp;nbsp;nbsp;.Bnbsp;nbsp;nbsp;nbsp;B

1 nbsp;nbsp;nbsp;39nbsp;nbsp;nbsp;nbsp;S

. nbsp;nbsp;nbsp;dnbsp;nbsp;nbsp;nbsp;d

�

lt;

S�

ft�

�

X P � p

E* p

3 a_

2 nbsp;nbsp;nbsp;p�

n ^

B �

2 a-0 nbsp;nbsp;nbsp;2

a a

2 d �

r S

a nbsp;nbsp;nbsp;�

d -*

�

p�

ft*

S�

�

p�

x�

S�

�

p�

1�

�I

�a

�

�_

p�

3�

�

72 72 � �

� �

2. 2. pquot; p�

X sa --

� �.

S 0*

� tr*

P �

� ?� a g

ft nbsp;nbsp;nbsp;O'

�

a ^

�.

a�

�

1�.

�

�lt;

�

tr*

�

S�

�

ft.

�

ft^

��

ft*

�

ftgt;

�lt;

ft�

'ft

�

�Kl

to nbsp;nbsp;nbsp;tonbsp;nbsp;nbsp;nbsp;to

C5 nbsp;nbsp;nbsp;C5nbsp;nbsp;nbsp;nbsp;C5

C5 nbsp;nbsp;nbsp;tonbsp;nbsp;nbsp;nbsp;to

to nbsp;nbsp;nbsp;totototototototo

C5 nbsp;nbsp;nbsp;OJOOlOitnOlWCl

gt;-� nbsp;nbsp;nbsp;i-�O?0�D-0*gt;.t0t0

totototototototo

h-��-O-OOWVitO

to nbsp;nbsp;nbsp;10nbsp;nbsp;nbsp;nbsp;tonbsp;nbsp;nbsp;nbsp;tonbsp;nbsp;nbsp;nbsp;to

CO nbsp;nbsp;nbsp;tonbsp;nbsp;nbsp;nbsp;tonbsp;nbsp;nbsp;nbsp;to

CO nbsp;nbsp;nbsp;�1nbsp;nbsp;nbsp;nbsp;tonbsp;nbsp;nbsp;nbsp;CO

0 Page.

� Virginia and North Carolina.

p�

! ^

Germany (Franconia, etc.).

: nbsp;nbsp;nbsp;H-

Sweden.

� nbsp;nbsp;nbsp;:

alt;

CD nbsp;nbsp;nbsp;1

China.

DD.50

-�ft B-

P 0 S

�ft

ft�

India (Rajmahal group,etc.).

England (Yorkshire, etc.).

�?

gt;

i Italy.

1 Russia.

Spitzbergen (Cape Boheman).

1 Eastern Siberia.

India (.Jabalpur group, etc.).

Japan.

Jlt;

1 France (Verdun, St. Mihiel).

-D p�2nbsp;r P

1-4 M ^ , Bavaria (Solenhofen).

W nbsp;nbsp;nbsp;V-

France (Morestel, Armaille, nbsp;nbsp;nbsp;1 W

etc.). nbsp;nbsp;nbsp;�3; 2

! England, including Purbeck

j beds. Isles of Wight and

1 Portland.

B ^00

^ of

M nbsp;nbsp;nbsp;H-

1 North Germany.

ft' nbsp;nbsp;nbsp;X P

1 TRussia (Klin).

Oo'

'ft

�l

Triassic.

tTurasaic.

Creta

ceous.

(2 O' s a o g o m 195	Species.	�yj e?	Rhmtic.			Rhoi-tic or Lias.	Lias.	Ooolite.							1 Goral-lian.		Kini- merid gian. �quot; a b. ��1 '� ^ � � a � � I b. Ph	quot;WealdcD.
	Species.		�� a quot;p O o p d d '5 �Su	o cT '5 c a 2 p d 3 o O	p �TS CC	!� .9 S u	� A o tc quot;d .s � p t-H	V o (1 o b a d % P W	gt;. M	d	'p d a lt;u Pi O M Oi P^ d O P a fee p p/ �p. �2	� .o � � d	� � a o � fee p p pO d 1;^ d P M	P d p. d	� H OQ pquot; -S � � � p d u	'p r� o �p � o ed d d pq		-^5 P 4* P.P Ph M P^ I'S � (T P � . S 'O � p^amp;	gt; p 1 b- � X t. �	'.quot;a i .S- �5 cc Jj p?
	JJracljypliyllum parcerainosuin, ii. sp ...		�� a quot;p O o p d d '5 �Su	o cT '5 c a 2 p d 3 o O	p �TS CC	!� .9 S u		V o (1 o b a d % P W	gt;. M	d		� .o � � d	� � a o � fee p p pO d 1;^ d P M	P d p. d	� H OQ pquot; -S � � � p d u	'p r� o �p � o ed d d pq		-^5 P 4* P.P Ph M P^ I'S � (T P � . S 'O � p^amp;	gt; p 1 b- � X t. �	'.quot;a i .S- �5 cc Jj p?
196	Brachjpliyllum, vspecies ? (cone)........	223
197	Bracliyphyllutu, species ? (cone)........	224
204	Leptostrobns ? species (c) seed.........	232										1
209	Torreya falcata, n. sp...................
218	Sequoia cycadopsis, n. sp...............	243			1

219	Sequoia Reichenbachi (Gein.) lieer____	243
221	Sequoia subulata Heer.................	245
222	Sequoia anibigua Heer.................	245
223	Sequoia rigida Heer...................	246
225	Sequoia gracilis Heer..................	247
22G	Sequoia delicatnla, n. sp................	247
230	Araucaria podocarpoides, n. sp.........	249
233	Taxodium rainosuni, n. sp..............	251
234	Taxodiura Virginicum, n. sp............	252
235	Taxodium expansum, n. sp.............	252
238	Taxodium Brookense, n.sp.............	254
240	Sphenolepidiiim parceramosum, n. sp-..	257
243	Splienolepidium pachyphyllum, n. sp...	259
244	Sphenolepidiiim Virginicum, n. sp......	259
245	Splienolepidium HiuTianura Heer......	260																	1
246	Sphenolepidiiim Sternberg! aniim	261																	1
	(Dunk.) Heer.
247	Sphenoleiiidium Stern bergian urn	2amp;1
	(Dunk.) Heer, var. densifolium, n. var.
248	Abietites macrocarpus, n. sp...........	262
251	Araiicarites Virginiciis, n. sp...........	263
255	Carpolithiis Virginiensis, n.sp..........	266										1
												1
				1	1											,

256	Carpolitlras agglomeratus,n.sp........1267

			FORMATIONS IN WHICH				THE SPECIES COMPARED							OCCUR.						Species with which compared.
Noocomian.				Urgoniaii.		Cr Gault.	etaceous. Cenoma nian.				Da kota. OD � d OQ 'd � �3 P	Seuouiaiv.					-	Lara mie. cS d P d � P d 05 � m � �5 P	� p � � o p 3� p � a � p � p � 'P P fee P PQ
o 'A . Pi.a � b- S-2 � CC � � T o o M	IS fen t- o Ok	'p � P d Pi tc p quot;p O .g p: p* 4J CO �	'5 40 � � P � o s � � p ff!	'�� p c W p 'p � � O	� O CO S i. 1? � � 02 P .03 �E 441 05	4^� d � C3 - 02 � U a quot;� P � � feO � � rO 'P. 02	��' 1 'p p � 5	� � af P :� Pp � � � g g H es 02	ffl gt; d O 'P d d g � Pi o PQ	a '� .p p o a Cm O � (H		p o �r* d � 5 fl H g '��onbsp;��nbsp;5- � �-5 12:; P2 � p '43 lt;0 r PQ	o o (S p S quot;p � � S	� '� d Pi O �3	i Pi p. 4A � �	� P rP � P O'	'p cd 05 � 3 � �gt;j H
o 'A . Pi.a � b- S-2 � CC � � T o o M	IS fen t- o Ok	'p � P d Pi tc p quot;p O .g p: p* 4J CO �	'5 40 � � P � o s � � p ff!	'�� p c W p 'p � � O					ffl gt; d O 'P d d g � Pi o PQ	a '� .p p o a Cm O � (H			o o (S p S quot;p � � S	� '� d Pi O �3	i Pi p. 4A � �	� P rP � P O'	'p cd 05 � 3 � �gt;j H




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Page.

Virginia and North Carolina.

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Page.

Virginia and North Carolina.

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Systematic number.

o pO a 3 C o a lt;�gt; in CC	Names of the species. ^	6 b� c3
91	T. Meehiana, var. angustiloba, n. sp.............	120
92	Thyrsopteris crenata, n. sp......................	127
93	Thyrsopteris iusignis, n. sp.....................	127
94	T. insignis, var. angustipennis, n. sp............	128
95	Thyrsopteris densifolia, n. sp....................	129
96	Thyrsopteris crassinervis, n. sp.................	130
97	Thyrsopteris decurrens, n. sp...................	130
98	Thyrsopteris aiigustifolia, n. sp ................	131
99	Thyrsopteris micropbylla, n. sp.................	131
100	Thyrsopteris pachyrachis, n. sp.................	132
101	Thyrsopteris elliptica, n. sp.....................	133
102	Thyrsopt-eris distans, ii. sp......................	134
103	Thyrsopteris angustiloba, n. sp.................	134
104	Thyrsopteris pachyphylla, n. sp .. .\............	135
105	Thyrsopteris pecopteroides, n. sp...............	135
106	Thyrsopteris pinnatifida, ii. sp..................	136
107	Thyrsopteris heteromorpha, n. sp..............	136
108	Thyrsopteris varians, n. sp......................	137
109	Thyrsopteris rhombifolia, n. sp.................	138
110	Thyrsopteris heteroloba, n. sp.................	139
111	Thyrsopteris bella, n. sp........................	139
112	Thyrsopteris microloba, n. sp ..................	140
113	T. microloba, var. alata, n. sp....................	140
114	Thyrsopteris nana, n. sp........................	141
115	Thyrsopteris ineequipinnata, n. sp.............	142
116	Thyrsopteris heterophylla, n. sp................	142
117	Thyrsopteris obtusiloba, n. sp..................	143
118	Thyrsopteris spbenopteroides, n. sp ............	143
119	Thyrsopteris squarrosa, n. sp...................	143
120	Thyrsopteris rhombiloba, u. sp..................	144
121	Thyrsopteris retusa, n. sp.......................	144
122	Osraunda spbenopteroides, n. sp................	145
123	Osmunda Dicksonioides, n. sp..................	146
124	0. Dicksonioides, var. latipenjiis, n. sp...........	147
125	Sagenopteris latifolia, n. sp.................	148
126	Sagenopteris elliptica, n. sp.....................	149
127	Sagenopteris Virginiensis, n. sp.................	150
128	Scleropteris elliptica, n. sp......................	151
129	S. elliptica, var. longifolia, n. sp.................	152
130	Scleropteris Virginica, n. sp....................	152
131	Scleropteris dentata, n. sp.......................	153
132	Ctenopteris insignis, n. sp.......................	156
133	Ctenopteris Virginiensis, n. sp..................	157
134	Ctenopteris integrifolia, n. sp...................	158
135	Ctenopteris angustifolia, n. sp..................	159
136	Ctenopteris minor, n. sp.........................	157
m	Ctenopteris longifolia, n. sp.....................	159

									P	p
B s a o quot;cf a 1 ki U2	Names of the species.	lt;s bx: �5 Ph	a o o � Ph a	.a V CB O� P H	quot;cl p cB � Ph P .d s fl	d 4� fl bl .9 GO	P 4 s lt;n cB 02	ti U �S �g 'd lt;0 ^-l pR	Ph u n 9 c o CR c� D P O s �S rS CQ O Ph	amp; u S5 s � o Ph u ei a P lt;�gt; S 3	(X O A a �d (M lgt;	� O o p pp (-1 a o P P W	05 P ai M	P � P c 0 o o O	p s .p �� bX) � H	p s o 05 P � w �	p � .9 05 S �	P C bl P s to cS	� � a *cB w	� c p cS M	P � C3 5 � � Pm ki CB � P � 'S bt 3	V to *�	00 '� � p O �
138	Zainiopsis pinnatifida, n. sp...................	161						1
139	Zamiopsis insii^nis, n. sp........................	162
140		164
141		164						1
142		166						1
143		167						1											1
144	Anomozamites Virgiuiciis, n. sp ....1...........	168							1						1
145	Platypterigium densinerve, n. sp................	169
146	Platypterigiam Rogersianum, n. sp.............	171						1
147	Zamites tenuinervis, n. sp......................	171			1	1		1							1
148		172						1
149	Zamites distautinervis, n. sp....................	172						1
150	Zamites ovalis, n, sp............................	173			1	1			1						1
151	Zamites subfalcatus, n.sp.....................	173
152	Encephalartopsis nervosa,n. sp.................	174						1
153		175						1
154		176						1
		176
156	Podozamites subfalcatus, n. sp.................	179									1
157	Podozamites distaniinervis, n. sp...............	179						1	1						1
158	Podozamites pedicellatus, n. sp.................	180						1
159	Podozamites graudifolius, n. sp.................	180						1	1
160	Podozamites acutifolius, n.sp...................	181	1			1		1	1			1			1
161		182			1	1	1						1		1	1	1
162	D. Buciiianus, var. obtiisifolius, n. sp............	184			1								1
163	D.Bucliiauus, var. angmstifolius................	185		1	1	1							1	1	1
164	Tysonia Marylaudica, n. sp.....................	193											1									1	1
165	Nageiopsis longifolia, n. sp......................	195	1		1			1			1				1							1	1
166	Nageiopsis zamioides, n. sp......................	196			1	1		1
167	Nageiopsis recurvata, n. sp......................	197			1	1		1
168	Nageiopsis crassicaulis, n. sp...................	198			1	1		1	1		1
169	Nageiopsis latifolia, n. 8p ......................	198				1			1
170		199							1
171		199						1
172		200							1
173		200											1
174		201											1		1
175		201				1		1
176		201				1		1	1
177		202				1		1	1		1	1			1		1
178		203									1
179	Phyllocladopsis heterophylla, n. sp..............	204				1
180	Phyllocladopsis heterophylla, n. sp..............	205
181		207		1	1	1		1
182		208		1	1	1
183		208		1	1	1
184	Baieropsisfoliosa, n.sp..........................	209		1								1				1

Geological formations.	Potomac species (systematic numbers on the left; page on which described on the right).		Species with which compared.
XV.�Wealden of Germany�	163. D. Bnchianus angustifolius Font......	185	Identical (= Pterophy Hum abietinum Gopp.
Continued.	244. Sphenolepidium Virginicum..........	259	and D. abietinus Miquel). S. Kurrianum Heer.
	245. Sphenolepidium Kurrianum Heer.....	260	Identical.
	246. Sphenolepidium Sternbergiannm	261	Do.
XVI.�Wealden of England..	(Dunk.) Heer. 2. Equisetum Lyelli Mant...............	65	Do.
	39. Sphenopteris Mantelli Brongn........	91	Do.
	164. Tysonia Marylandica.................	193	Bennettites.
XVII.-AVealden ? (Neoco-	8. Cladophlebis falcata..................	72	Mantellia. Pecopteris Whitbiensis Brongn.
mian?) of Klin, Kussia.	11. Cladophlebis oblongifolia.............	74	Do.
XVIII.�Jurassic? (Weal-	17. Cladophlebis alata....................	77	Pecopteris exiliformis Geyl.
den? Neocoroian?) of Ja-	86. Thyrsopteris rarinervis...............	123	T. elongata Geyl.
pan.	160. Podozamites acutifolius...............	181	P.lanceolatus.(L. amp; H.) Brongn.
	169. Nageiopsis latifolia...................	198	Podozamites Beinii Geyl.
XTX.�Xeocomian (Koota-	234. Taxodium Virginicum................	252	Glyptostrobus Gronlandicus Heer.
nie) of Brit. NW. T.
XX.�Neocomian of Portu-	39. Sphenopteris Mantelli Brongn........	91	Identical.
gal.	52. Aspidium Dunkeri (Schimp.) Font____	101	Do.
	244. Sphenolepidium Virginicum..........	259	S. Kurrianum Heer.
	245. Sphenolepidium Kurrianum Heer____	260	Identical.
	246. Sphenolepidium Sternbergianum	261	Do.
XXI.�Neocomian of West-	(Dunk.) Heer. 246. Sphenolepidium Sternbergianum 261		Do.
phalia. XXII.�Neocomian? of	(Dunk.)Heer. 251. Araucarites Virginicus...............	263	Araucaria cretacea Brongn.
France.
XXIII.�Urgonian of Green-	4. Cladophlebis constricta...............	68	Pecopteris borealis Brongn.
land.	12. Cladophlebis crenata..................	75	Pecopteris borealis Brongn.
	56. Polypodium fadyenioides.............	104	Nathorstia angustifolia Heer.
	78. Gleichenia Nordenski�ldi? Heer.....	119	Identical.
	79. Undetermined fern...................	119	Asplenium Dicksonianum Heer.
	82. Thyrsopteris Virginica �!...........	120	Dicksonia Jobnstrupi Heer.
	86. Thyrsopteris rarinervis................	123	Asplenium Dicksonianum Heer.
	93. Thyrsopteris insignia.................	127	Asplenium Jobnstrupi Heer.
	193. Frenelopsis parceramosa.............	218	F. Hoheneggeri (Ett.) Schenk.
	209. Torreya falcata.....................	235	T. parvifolia Heer.
	219. Sequoia Reichenbachi (Gein.) Heer ..	243	Identical.
	222. Sequoia ambigua Heer ...............	245	Do.
	223. Sequoia rigida Heer...................	246	Do.
	225. Sequoia gracilis Heer................	247	Do.
	234. Taxodium Virginicum...............	252	T. (Glyptostrobus) Gronlandicum Heer.
	247. Sphenolepidium Sternbergianum var. 261		Sequoia fastigiata (Sternb.) Heer.
XXIV.�Urgonian of Aus-	densifoliura Heer. 154. Glossozamites distans................	176	G. Zitteli (Scbenk) Schimp.
trian Silesia.	156. Podozamites subfalcatus.............	179	Zamites ovatus (L. amp;H.) Morr.
	161. Dioonites Buchianus Schimp.........	182	Z. afiBnis Schenk. Z. nervosus Schenk. Identical.
	165. Nageiopsis longifolia.................	198	ZamitesGcepperti Schenk?
	181. Baieropsis expansa..................	207	Baiera cretosa Schenk.
	193. Frenelopsis parceramosa.............	218	F. Hoheneggeri (Ett.) Schenk.

Geological formations.	Potomac species (systematic numbers on the left; page on which described on the right).		Species with which compared.
XXX.�Dakota Group,	352. Platanophyllum crassinerve..........	316	Hedera platanoidea Lx.
United States�Continued.	353. Araliaepbyllum obtusilobum..........	317	1
	354. Aralisepuyllum acutilobum............	318	Sassafras recurvatura Lx.
	355. Araliscphyllmn magnifolium..........	318	1 Liquidambar integrifolium Lx.
	356. Aralisephvlhim aceroides..............	319	1
XXXI �Senonian of Patoot,	221. Sequoia subulata Heer................	245	Identical.
Greenland.	223. Sequoia rigida Heer...................	246	Do.
	226. Sequoia delioatula.....................	247	S. subulata Heer.
	240. Sphenolepidium parceramosum.......	257	Sequoia coiudnna Heer.
	247. Sphenolepidium Sternbergianum, var.	261	Sequoia fastigiata (Sternb.) Heer.
	densifolium Heer. 311. Ficophyllum serratum................	294	Quercus .Tobnstrupi Heer.
XXXII.�Senonian of	218. Sequoia cycadopsis....................	243	Cycadites Unjiga Daw.
British America.	219. Sequoia Reichenbachi (Gein.) Heer...	243	Identical.
	309. Ficophyllum crassinerve..............	291	Ficus maxima Daw.
XXXIII.�Senonian of Qued-	219. Sequoia Reichenbachi (Gein.) Heer ...	243	Identical.
linburg.
XXXIV.�Senonian {Gosau)	219.......Do..............................	243	Do.
of Tyrol.	223. Sequoia rigida Heer...................	246	Do.
	233. Taxodium ramosum...................	251	AViddringtonites Reichii (Ett.) Heer.
	235. Taxodium expansum..................	252	Sequoia heterophylla.
XXXV.�Senonian of West-	219. Sequoia Reichenbachi (Gein.) Heer ...	243	Identical.
phalia.	244. Sphenolepidium Virginicum..........	259	Sphenolepidium Kurrianum Heer.
	245. Sphenolepidium Kurrianum Heer.....	260	Identical.
	246. Sphenolepidium Sternbergianum	261	Do.
XXXVL�S e n 0 n i a n of	(Dunk ) Ileer 219. Sequoia Reichenbachi (Gein.) Heer ...	243	Do.
Aachen.
XXXVII.�Laramie group..	219.......Do..............................	243	Do.
XXXVIII.�Eocene of Eng-	230. Araucaria podocarpoides..............	249	Podocarpus incerta Ett. amp; Gard.
laud.	304. Rogersia longifolia ....................	287	Glossochlamys transmutans Ett. amp; Gard.

to $ a o quot;S � oo gt;gt; CC	NaraoH of the species.	� bfl amp;
1	Equisetum Virgiuicum, n. sp...................	63
2	Equisetum Lyelli Mant.........................	65
3	Equisetum Marylandicum, n. sp................	65
4	Cladophlebis constricta, n. sp....................	68
6	Cladoplilebis latifolia, n. sp .....................	69
6	Cladoplilebis Virginiensis, n. sp................	70
7	Cladophlebis denticulata, n. sp.................	71
8	Cladoplilebis falcata, n. sp.......................	72
9	Cladophlebis parva, n. sp........................	73
10	Cladophlebis acuta, n. sp........................	74
11	Cladophlebis oblongifolia, n. sp ..................	74
12	Cladophlebis crenata, n. sp......................	75
13	Cladophlebis, species............................	76
14	Cladophlebis inclinata, n. sp....................	77
15	Cladophlebis distans, n. sp......................	77
16	Cladophlebis, species............................	77
17	Cladoplilebis alata, n. sp.........................	77
18	Cladophlebis rotundata, n. sp.....................	78
19	Cladophlebis, species............................	78
20	Cladophlebis sphenopteroides, n. sp.............	79
21	Cladophlebis petiolata, n. sp.....................	80
22	Cladophlebis iumquiloba, n. sp..................	80
23	Cladophlebis brevipennis, n. sp .................	81
24	Cladophlebis, species............................	81
25	Cladophlebis pachyphylla, n. sp.................	80
26	Pecopteris Virginieiisis, n. sp...................	82
27	Pecopteris siriotiiiervis, n. sp...................	84
28	Pecopteris ovatodentata, n. sp...................	85
29	Pecopteris miorodonta, n. sp....................	85
30	Pecopteris constricta, n. sp......................	86
31	J�ecopteris brevipennis, n. sp....................	86
32	Pecopteris socialis Heer ........................	87
33	Pecopteris angustipennis, n. sp..................	87
34	Pecopteris Browniana Dunk....................	88
35	Pecopteris pachyphylla, n. sp......-...........	88
36	Sphenopteria thvrsopteroides, n. sp.............	89
37	Sphenopteris acrodentata, n. sp..................	90
38	Sphenopteris latiloba, n. sp.....................	90
39	Sphenopteris Mantolli Brongn..................	91
40	Sphenopteris spatulata, n. sp..................	93
41	Sphenopteris pachyphylla, n. sp................	93
42	Aspidium Fredericksburgense, n. sp............	94
43	Aspidium cllipticum. n. sp......................	95

lt;�gt; B S o a B lt;D 02	Names of the species.	03 fee c8 pH
44	Aspidiuni heterophyllum, ii. sp.................	96
45	Aspidium Yirginicunj, n. sp....................	97
46	Aspidium angustipiimatum, n. sp...............	98
47	Aspidiam cystopteroides, n. sp................	99
48	Aspidmin Oersted! ? Heer.....................	99
49	Aspidium oblongifolium, n. sp..................	100
50	Aspidium parvifolium, n. sp....................	100
51	Aspidium pinnatifidum, n. sp ..................	101
52	Aspidium Dunkeri Schimp., sp.................	101
53	Aspidium dentatum, n. sp......................	102
54	Aspidium macrocarpnm, n. sp..................	103
55	Aspidium microcarpum, n. sp...................	103
56	Polypodium fadyenioides, n. sp.................	104
57	Polypodium dentatum, n. sp....................	105
58	Acrostichum crassifolium, n. sp................	105
59	Acrostichopteris longipennis, n. sp.............	107
60	Acrostichopteris densifolia, n. sp...............	107
61	Acrostichopteris parvifolia, n. sp...............	108
62	Acrostichopteris parcelobata, n. sp.............	108
63	Acrostichopteris cyclopteroides, n. sp..........	109
64	Asplenium dubium, n. sp.......................	109
65	Thinnfeldia variabilis, n. sp....................	110
66	Thinnfeldia granulata, n. sp....................	111
67	Thinnfeldia rotuudiloba, n. sp..................	111
68	Stenopteris Virginica, n. sp,....................	112
69	Angiopteridiura auriculatum, n. sp.............	113
70	Angiopteridium nervosum, n. sp...............	114
71	Angiopteridium ellipticum, n. sp ...............	114
72	Angiopteridium densinerve, n. sp ..............	115
73	Angiopteridium pachyphyllum, n. sp...........	115
74	Angiopteridium ovatum, n. sp..................	115
75	Angiopteridium strictinerve, n. sp.............	116
76	A. strictinerve, var. latifolium, n. sp...........	116
77	Angiopteridium dentatum, n. sp................	117
78	Gleichenia Nordenskioldi ? Heer...............	119
79	Undetermined fern, n. sp......................	119
80	Aspleniopteris pinnatifida, n. sp................	118
81	Asplcniopteris adiantifolia, n. sp...............	118
82	Tliyi'sopteris Virginica, n. sp...................	120
83	Thyrsopteris brevifolia, n. sp...................	121
84	Thyrsopteris dentata, ii. sp......................	121
85	Tbyrsopteris nervosa, n. sp.....................	122
86	Thyrsopteris rarinervis, n. sp...................	123
87	Thyrsopteris brevipennis, n. sp.................	124
88	Thyrsopteris alata, n. sp........................	124
89	Thyrsopteris divaricata, n. sp...................	125
90	Thyrsopteris Meekiana, n. sp...................	125 1

OD7- SaZ

LIBRARY CATAI.OGUE SIRPS.

_A.DVERTISEMEMT.

1889. 8�. 55 pp. 10 pi. Price

United States Geological Survey

UNITED STATES GEOLOGICAL SURVEY

THE POTOMAC

CONTENTS

ILLUSTRATIONS.

VIII

ILLUSTEATIONS.

ILLtJSTEATIONS.

IX

ILLUSTRATIONS.

ILLUSTRATIONS.

XI

ILLUSTRATIOXS.

LETTER OF TRANSMITTAL.

Hon. J. W. Powell,

THE POTOMAC OR YOUNGER MESOZOIC FLORA.

DESCRIPTION OF THE SPECIES.

ZAMIOPSIS, gen. nov.

PHANEROGAMS.

ANOMOZAMITES Schimper.

OYMNOSPERMOUS FRUITS.

SAPINDOPSIS, gen. nov.

ABALIA L.

326

LIST OP POTOMAC FOSSIL PLANTS.

327

328

THE POTOMAC OK YOUNGER MESOZOIC ELOEA.

LIST OP POTOMAC FOSSIL PLANTS.

THE POTOMAC OE YOUNGEE MESOZOIC FLOEA.

350

Table I.�List of species of the rotomac formation, loith the localities at which thet) were collected.

TABLES.

351

Table I.�List of species of the Potomac formation, with the localities at which they were collected�Cout�d.

352

THE POTOMAC OR YOUNGER MESOZOIC FLORA.

Table I.�List of species of the Potomac formation, with the localities at which they were collected�Cont�d.

TABLES.

Table I.�List of species of the Potomac formation, with the localities at which they were collected�Cont�d.

THE POTOMAC OR YOUNGER MESOZOIC FLORA.

Table I.�List of species of the Potomac formation, with the localities at tchich they were collected�Coated.

TABLES.

355

Table I.�List of species of the Potomac formation, xoith the localities at which they were collected�Cont^d.

THE POTOMAC OR YOUNGER MESOZOIC FLORA.

..i 1

TABLES.

Table I.�List of species of the Potomac formation, with the localities at which they tvere collected�ContM.

358

THE POTOMAC OR YOUNGER MESOZOIC FLORA.

TABLES.

359

Table II.�List of species of plants of the Potomac formation identical

with or allied to species described fromothei' localities and formations.

358 nbsp;nbsp;nbsp;THE POTOMAC OR YOUNGER MESOZOIC FLORA.

Table II.�List of species of plants of the Potomac formation identical

TABLES.

with or allied to species described from otho' localities and formations.

359

360 nbsp;nbsp;nbsp;THE POTOMAC OR YOUNGER MESOZOIC FLORA.

Table II.�List of species of plants of the Potomae formation identical

TABLES.

with or allied to species described from other localities and formations�Continued.

361

360 nbsp;nbsp;nbsp;THE POTOMAC OE YOUEGEE MESOZOIC FLOE A.

TABLES.

361

THE POTOMAC OK YOUKGEK MESOZOIC FLORA.

Table II.�List of species of plants of the Potomac formation identical

TABLES.

with, or allied to species described from other localities and formations�Continued.

362 nbsp;nbsp;nbsp;THE P�TOMAO OE YOUNGEE MESOZOIC FLOEA.

Table II.�List of species of plants of the Potomac formation identical

TABLES.

with or allied to species described from other localities and formations�Continaed.