ter verkrijging van den graad van
doctor in de wis- en natuurkunde
aan de rijks-universiteit te utrecht,
op gezag van den rector-magnificus
dr. c. g. m. de vooys, hoogleeraar in
de faculteit der letteren en wijs-
begeerte, volgens besluit van den
senaat der universiteit tegen de be-
denkingen van de faculteit der wis-
en natuurkunde, te verdedigen op
maandag 28 november 1932, des na-
middags te 3 uur

Allen, die op eenigerlei wijze hebben bijgedragen tot het tot stand komen
van dit proefschrift, zij mijn dank gebracht.

In de eerste plaats geldt mijn dank U, Hooggeleerde Rutten, Hooggeachte
Promotor. Ik ben U erkentelijk bovenal voor de wijze waarop Gij mijn studie
hebt geleid en voor den invloed, dien Gij op mijne persoonlijke ontwikkeling
hebt gehad.

Ofschoon dit proefschrift niet onder Uwe leiding geschreven werd. Hoogge-
leerde ScHMUTZER, heb ik toch menigmaal van Uw kennis en inzicht, tot mijn
voordeel, gebruik kunnen maken.

Hooggeleerde Nierstrasz, wanneer ik terugdenk aan den tijd, dat ik mij
bekwaamde in de zoölogische wetenschap, dan verheug ik mij nog steeds over
de zoo buitengewoon pleizierige wijze waarop ik onder Uw leiding heb kunnen
werken.

Uwe colleges. Hooggeleerde Brouwer, vermeerderden mijn kennis aan-
gaande tektonische vraagstukken.

Mijn belangstelling voor de bodemkunde dank ik U, Hooggeleerde Möhr.
Ik zal niet vergeten de aangename manier waarop Gij dit vak doceert.

Het doet mij goed, Hooggeachte Mevrouw Rütten, U hier nog eens te kunnen
bedanken voor de zorgen, waarmede Gij immer de leden van de „Antillen-
expeditie 1930quot; omringdet.

Hun, die in 1930 op de verschillende West-Indische eilanden ons behulpzaam
waren bij de voorbereiding van het veldwerk, ook mijn speciale dank. Ik denk
hier vooral aan de gezaghebbers, de leiders van de Cura^aosche Petroleum
Industrie Mij. en de plantage-eigenaren.

Het spreekt wel vanzelf dat nooit de herinnering zal verloren gaan aan jullie,
collega's expeditie-genooten, Mac Gillavry, Pijpers, Rutten Jr., Vermunt
en Wagenaar Hummelinck.

Waarde Van Dijk, de uren die Ge — tezamen met mij — doorbracht met
werk voor dit proefschrift zijn vele. Wees er van verzekerd, dat die uren voor
mij zijn geweest, tijden van bijzondere gezelligheid.

Waarde Grootveld en Vermeer, Ulieden dank ik voor het verrichten van
het vaak eindeloos lijkende slijpwerk.

Maar Hij die U kent, die kan het weien
Wat schoons Gij hem heeft aan te hiên,
En nimmer zal hij dat vergeten,
't Natuurschoon wat U hem liet zienquot;.

These considerations on the geology of Aruba, the smallest island of the
Dutch Leeward Islands of the Lesser Antilles, are the result of a geological
excursion in the summer of 1930 under the leadership of Prof. Dr. L. Rutten,
University of Utrecht (Holland). Aniliia was surveyed for about 22 days by three
groups of two geologists. The survey was done with the help of the geologists
H. J. Mac Gillavry, P. J. Pijpers, M. G. Rutten and L. W. J. Vermunt.
I give thanks here to those who rendered us good service during our stay on the
island, especially to the governor of Aruba, Mr. L. Wagemaker, to lieutenant
C. Janssens, to the propietor of the plantation Fontein, and to the drivers of
the sand motor-trucks, who so many times gave us a lift.

The material brought together has been examined in the Geological-Miner-
alogical Institute in Utrecht, and is kept there (numbers A; the numbers D
are the slides of the rocks). Besides, rocks have been studied which were sampled
by 1. Boldingh in the years 1909—1910 (numbers P, also in the Utrecht
collections), those, sampled by Prof. K. Martin and described by Prof. J. H.
Kloos in the years 1885—1889 (in the Rijksmuseum van Geologic en
Mineralogie, at Leiden), and those collected by Prof. J. A. Grutterink in the
year 1909 (Pétrographie collection in the Gebouw voor Mijnbouwkunde in Delft).

Concerning the rock description the following must be remarked. Little or
no attention has been paid to the true crystallograpliic and mineralogical proj)-
erties of the constituent minerals. On the other hand, their mutual relation in
the rock has been specially studied. In accordance herewith, the composition of
the plagioclases has not been determined with the von Fedorow method but
with the help of the tables of Weinschenk (51). As to the granularity and the
magnitude of the crystals, they have been indicated in the rock descriptions in
the way as suggested by Iddings (21, p. 192). Moreover, here and there the size
of some special crystals has been added between brackets. The names texture and
.structure have been used in the English sense, not in the sense of Rosenbusch
(see f.i. the Geological Nomenclator of the Geologisch-Mijnbouwkundig Genoot-
schap voor Nederland en Koloniën. 1929). Chemical analyses of the examined
rocks could not be given because of the great expense involved.

In order to show the denseness of the network of observations the map fig. 1
has been added in which the points of observation have been marked down.

The boundaries of the different formations and subformations could be
marked down in the geological map without great difficulty. Nevertheless, the
establishment of some boundaries is rather dependent on subjective judgments
f.i. those between the limestone and the diorite detritus and between the diorite

and diorite detritus. As far as is possible and necessary the different differentiates
in the batholith have been indicated in the map, as well as the subformations
of the oider system. By no means I have aimed at completeness in this matter.

The survey has been done with the help of the topographic map of Aruba
1-. 20.000. This map lends itself excellently to orientation in the field and to the

As to the soil of Aruba, and also of Curasao and Bonaire, samples of this
soil from different places in the isles, taken and provided with annotations by
us, are in the collection of the Koloniaal Instituut in Amsterdam (Holland).

1) During the survey we had much profit from the observations made by Prof. K. Martian
in 1885 (30), and from his geological map. Since Martin only stayed a few days on the
island, it can be understood that we — in 1930 — were able to introduce several corrections
both with regard to the geology and the petrography.

The most important geological description is that by K. Martin (30) 1888.
The rocks sampled by him have been described by J. H. Kloos(25) 1887—1889.
The Aruba fossil Mollusca have been described by J. Lorié (29) 1887 and by
M. M. ScHEPMAN (see the list of determinations in Martin's book pp. 125—127,
1888). About the older literature and maps known already to Martin we can
refer to his book pp. 1—6. In the quot;Bijdragen en MededeeUngen van het Historisch
Genootschap, gevestigd te Utrechtquot; 51ste deel, 1930 Mr. B. de Gaay Fortman
communicated quot;Brieven van den Commissaris-Generaal voor de (Nederlandsche)
West-Indische bezittingen J. van den Bosch aan den minister voor de marine
en de koloniën (1827—1829)quot;, in which on pp. 241—247 a very short mentioning
of the Aruba rocks and of the occurrence of gold can be found. Martin did not
refer to A. Stelzner (44) 1877, who described amongst others limestone and
phosphate of Aruba.

After 1888 the following publications came out. Vaughan published in
1901 (46) an article on fossil corals. In the years 1915 (47) and 1921 (48 and 49)
he wrote more summarizing articles about the younger geology of the West-
Indies, in which also Aruba occupied a place. E. D. van Oort (33) 1902 descri-
bed some vertebrae out of the Colorado phosphate and discussed their age.
E. SuESZ (45) 1908—1909 treated the geology of Aruba only in the general view
of the Antilles as a whole. P. Chemin Dupontès (9) 1909 only made some remarks
on the Aruba gold and phosphate mining. G. Duyfjes published some articles
about gold and phosphate mining, 1911 (14) and 1915 (16), and also a description
of the Aruba landscape 1911 (15). A. Jesurun 1911 (24) and an unknown author
1910 (1) and ?1916 (2) devoted articles to the phosphate and its exploitation.
I. Boldingh 1914 (6) gave on pp. 127—128 in his quot;Flora of the Dutch West
Indian Islandsquot; a very short geological description of Aruba. In the added map
0Î the calcareous and non-calcareous soil oî Aruba he indicated already - although
wrongly - the large diorite outcrops in the SE-part of the island, which had not
been found by Martin (see also the description). In the Encyclopaedie van West-
Indië 1914—1918, Schepman wrote the chapter quot;Molluscaquot; (41), in which also
the Aruba Molluscs are treated. A zoological and zoogeographic study of H.
Burrington Baker 1924 (8) about the land and freshwater molluscs is of impor-
tance for the study of the younger geology of the islands. W. H. Hobbs (20) 1925
compared 'the Curaçao — Bonaire Arclet' with other Island Arcs and remarked
something on the intrusive cores of the islands, the reef-caps and the anticlinal
structure of the latest folding (pp. 255—257). L. M. R. Ruiten published in
1931 (38) a résumé of the palaeontological knowledge of the Dutch West-Indies.

Aruba is a low island of about 186 square km., just N of the Venezuelan
peninsula of Paraguana, separated from the latter by a sea, the greatest depth
of which is about 200 m. The main axis of the island has a direction about N W-SE.

The island consists of three formations, all being quite different in age and
in the nature of rocks:

The age of the former could not be determined, in consequence of the absence
of index fossils. In connection, however, with the occurrence of similar formations
of Cretaceous age on other Antilles, we can consider this older Aruba formation
to be also of Cretaceous age. This formation crops out - chiefly in the central
part of the island - in a hilly landscape in which the highest points of the island
occur: Jamanota (188m.), Arikok (185 m.), Seroe Kabaai (170 m.). Gran Tonel
(155 m.). The principal rocks are diabases, uralite-diabases, diabase-tuffs (partly
with Radiolaria), hornblende-schists and diabase-conglomerates. They constitute
a volcanic complex with scanty foreign material. The diabase pebbles of the
conglomerates seem to have their origin in a country between Aruba and Curasao.
The whole formation has been strongly folded. The folding can be recognized,
however, only in the stratified rocks, which mainly show an almost vertical
position and an E-W strike. The orogenic processes took place in older Tertiary
(lower Eocene) or in youngest Mesozoic time. During this orogenesis the dionte
batholith intruded into the older system (compare with similar intrusions on
other West-Indian Islands) and a great part of the rocks of the latter has been
metamorphosed in consequence of the contact action. Over a distance of about
2 km from the visible contact the diabases have been changed into uralite-
diabases, the tuffs into hornblende-schists (also in consequence of the dynamo-
metamorphism). Nearer the contact the rocks have been changed into strongly
contactmetamorphic rocks, being amphibolites and amphibole-plagioclase-rocks.
The latter rocks show in many places a strongly hybrid character and merge
into the diorite. They occur also as inclusions in the diorite.

1) See for tlie geomorphology also Martin (30) p. 40 'Orographische Gliederung';
the numbers indicating here the altitude arc wrong.

It is impossible to say whether a partial roof-foundering took place during
the intrusion, or not. In any case a great part of the roof (the older rocks) must
have been eroded after the intrusion, so that today the quartzdiorite batholith
occupies the greater part of Aruba. It has been denuded to a rather low level
with an average altitude of about 40 m. (5—130 m.). The highest diorite hills he
along the NE-coast and in SE-Aruba. In distinction from the landscape of the
older rocks the diorite landscape is generally a flat one, in which numerous
quot;Felsenmeerequot; of big, roundish and exfoliated diorite blocks can be found (selec-
tive erosion). - The batholith is composed of many kinds of rock differentiates.
The most common rock in it is quartzdiorite with hornblende and biotite as dark
minerals. First-solidification-differentiates, older than and intruded by diorite,
are hooibergite-rocks and gabbroic rocks. The former occur in the landscape as
more or less steep hills and elevations, obviously preserved by selective erosion.
A fine example is the high and cony Hooiberg (164 m.). The hooibergites consist
mainly of hornblende, monoclinic pyroxene, plagioclase and quartz, and differ
in texture from the diorites and gabbros. The gabbroic rocks can be found espe-
cially in the large massive of the Matividiri and adjacent hills. They are normal,
quartz-bearing and partly hypersthene-bearing, gabbroic rocks, which have
been strongly hornblendized and uralitized where they border on the younger
diorite (contactmetamorphism). Granodioritic and granitic rocks seem to be of
the same age as the diorites; they occur but here and there in the batholith.

The younger representatives of the magmatic sequence occur as dikes, not
only in the batholithic rocks, but also in the rocks of the older formation. Con-
sequently, the diorite batholith must also be present not far under the surface
of this older formation. The dikerocks are dike-diorites, dike-granites, dike-
granodiorites, diorite-porphyrites, vintlites, malchites (and other melanocratic
rocks), dioritic aplites, granitic aplites, granodioritic aplites, quartz-albitites,
gabbro-aplites, pegmatites. Very young magmatic and hydrothermal dike- and
vein-rocks are quartz-rocks, quartz-epidote-rocks and epidote-rocks. The por-
phyritic dikes occur mainly along the N- and NE-coast. The strike of many of
them does not differ much from the E-W direction (compare with the strike
of the older schists).

The limestone lies unconformably on the two older rockformations, which
must have been partly denuded before its deposition. Only a part of the island
was under sealevel during the deposition, for almost the whole limestone complex
contains diorite material. The limestone covering has been partly denuded and
today it is found especially in SE-Aruba, as a zone, about 2 km. wide, along the
S- and W-coast, and as a narrow, frequently interrupted border along the N-
and NE-coast. The higher-situated beds show a clear dip and must have belonged
to a slightly arched limestone-cap over a part of the island. These beds border
on the sea-side on the lower and younger, about horizontal limestone terrace.
The limestone is chiefly Quaternary Lithothamnium-limestone which also contains
other organisms. Only in one place, on the high p'ateau in-SE-Aruba, a Tertiary
limestone, containing Lepidocyclina, has been found. The limestones in the SE-
corner of the island have been phosphatized.

Large deposits of diorite detritus especially occur along the S- and W-coast,
brought there by the quot;rooienquot; (small rivers which contain water only in the
rainy season). Although the deposition must have taken place already before and
during the deposition of the limestone, the greater part of the visible detritus
must be younger than and lies on the limestone terrace. - The coastdunes are
very young and occur along the E-, NE-, N- and W-coast (tradewinds). - Some
handshaped inlandbays with a junctioncanal to the sea can be found; they are
either entirely or almost entirely dry (f.i. Druif, Spaansch Lagoen). - The N-,
NE- and E-coast is on the whole steep and shows many undercuts, wavecut
chasms and coves in the rocks, the socalled quot;boca'squot; (tradewinds). In distinction
herewith, the S- and W-coast is in general low and flat (except in the places where
the terrace borders on the sea). Lying before and parallel to the S-coast a long,
narrow, frequently interrupted shore-coralreef rises for the greater part above
sealevel. In front of the W-coast only separate coralstocks are met with. These
reefs and stocks occur on a submarine platform, maximum to about 10 m. deep.
The shore-reef lies on the seaside of this platform and is separated from
the coast by a lagoon. Just SW of this reef the depth increases fast, maximum to
about 200 m.

This formation, consisting of diabasic rocks, schistose rocks, tuffoid rocks,
conglomerates and breccias, is the oldest on Aruba. It occurs chiefly in the central
part of the island, but it is also present in two smaller outcrops between Fontein
and Rincon, on the Seroe Pretoe (N of Savaneta), in the northwestern comer of
the island and in some other places. The rocks of this system are strongly folded,
in such a way that individual folds cannot be recognized. The average strike is
about N 90 E. The process of folding did not manifest itself very clearly in the
diabasic rocks. Where the formation borders on the diorite batholith, its rocks
show a clear contactmetamorphism. Consequently, the dioritic magma must have
been intrusive into this formation and the batholith must be younger. The many
dikes of diorite-differentiates in the formation, and the occurrence of many
diabasic and schistose inclusions in the diorite (exogenous inclusions) point to
the same relation in age. Hence, this formation is in fact the roof of the diorite
batholith.

Diabase-rocks constitute a great part of the older formation (see the map).
The bulk of the examined diabases are phanerocrystalline. The normal diabases
are generally phanerocrystalline; the aberrant and micro-porphyritic ones are
generally aphanitic. The diabases and the uralite-diabases could not be distinctly
separated, since the pyroxene of the former shows a beginning and an advanced
alteration in many rocks and since the pyroxene of the latter is not altogether
altered in some rocks. Hence, transitional types must be present but they have
been described in one of the two groups.

Macroscopically they are fine- to mediumgrained, rarely coarsegrained; dark- or lighter
coloured, grayish or greenish; they have here and there a brown or reddish-brown crust
of weathering.

Microscopic description: Most of the rocks are ophitic; the texture in D 12542 and
D 12543 is ophitic to hypidiomorphic-granulose-gabbroic. Therefore, the diabase A 478—
D 12542, which is medium- to coarsegrained, can be called a gabbro-diabase. The main
constituent minerals are plagioclase and monoclinic pyroxene. There is less or more pyroxene
than plagioclase. It is noteworthy, that the rocks with a partially hypidiomorphic-granulose-
gabbroic texture contain more plagioclase than pyroxene. A number of diabases contain
quartz, primary or secondary.

Plagioclase: The crystals are laths or prisms. In D 12535 and D 12547 tliey occur
locally in sheaf-like bundles. The plagioclases show polysynthetic twinning. The original

composition ranges from bytownite to oligoclase-andesine, and is mostly about labrador;
some of these plagioclases show a beginning albitization along fissures. A few rocks only
contain totally albitized plagioclases. Except in the latter rocks, several crystals are simply
zonal. The plagioclases are more or less epidotized and sericitized. Bent crystals occur in
some rocks. In a part of the rock D 12539 the plagioclase laths have been altogether changed
into a grainy quartz-plagioclase aggregate, rich in epidote. In D 12544 too a bytownite
aggregate took the place of the bigger and idiomorphic crystals in several spots and lies
now between the pyroxenes. The plagioclase laths and prisms of D 12541 do no more exist
as such, but have been wholly replaced by quartz, which occurs as grains between the pyro-
xenes, and by much epidote; the original lath- and prism-shape has partly been preserved,
so that in this rock too an ophitic texture can be recognized.

The pyroxene is an almost colourless to very lightgreen diopsidic augite. Dependent
on the relative number and the crystal-development of the plagioclases, the pyroxene
crystals are only allotriomorphic between the more or less idiomorphic plagioclases or are
quite 'cut up' by the plagioclase laths. In the former case, prismatic shape can be seen here
and there; in other cases the pyroxenes are quite shapeless. The diabases with an ophitic
to gabbroic texture also contain hypidiomorphic pyroxenes. The pyroxenes in D 12535
are partly conformed to the plagioclase laths, partly well-developed as long and narrow
prisms. A few pyroxenes are twinned.

Alteration: In by far the most of the diabases the pyroxenes are partly, to a greater or
smaller extent, uralitized and - in a further stage - chloritized. The crystals show different
phases of uralitization, that is to say, a beginning uralitization along the borders and cleavage
(fissures) unto a total alteration. In most of these rocks the uralite has been partly altered
into chlorite; here and there, the transitional phases between pyroxene, uralite and chlorite
are obvious. In many rocks the pyroxenes have altogether or partly a light-brownish colour
especially along the borders or as spots; it is probable, that this brown colour indicates the
first stage in the alteration process pyroxene —gt; uralite.

The uralite is lightgreen-pleochroitic, parallel- or diverse-fibrous. Plagioclase and uralite
are not quite sharply bordered on each other, for the uralite fibres radiate into the plagio-
clases; the latter also enclose many diminutive hornblende needles. In the rocks D 12537,
D 12540, D 12544 and D 12547 uralite occurs too as non-fibrous, undivided crystals, with
normal hornblende-cleavage and twinning here and there. These hornblendes, which are
also allotriomorphic, occur besides fibrous uralite and represent probably no primary
hornblende but the final stage of uralitization. This kind of uralite-hornblende occurs only
in the western part of the diabase-massive; so, it must have come into existence in connec-
tion with the neighbourhood of the diorite intrusion (S of Kleine Jamanota, Arikok, E of
Arikok, and Noordkaap); compare with the uralite-diabases.

The chlorite is lightgreen-pleochroitic, consists of fibres with steelblue interference-
colours or of spherolites with lightbrownishgreen interference-colours. The chlorite, being
altered pyroxene, is allotriomorphic between the plagioclases; moreover, chlorite may
occur in them.

The pyroxenes in D 12543 contain, moreover, biotite along fissures; in the same rock
chlorite seems to have originated from biotite (transitions!). In the rock D 12535 many
pyroxenes, here and there with a good octangular shape, but on the whole as badly idio-
morphic prisms, have been changed into Pserpentine and chlorite, parallel-fibrous and very
lightgreen; the serpentinization especially occurs along irregular fissures and along the
borders. Here and there remnants of the pyroxene seem to lie in this secondary mass. In
the same rock chlorite occurs moreover as irregularly shaped and small masses between
the quartz grains and also conformed to the plagioclases.

Hornblende: Primary green hornblende seems to be present in D 12536 and D 12548;
in these rocks no true uralite could be found. The hornblende takes up only little room,
and is quite allotriomorphic between or 'cut up' by the plagioclases; a single crystal shows
twinning. The greater part of it has been altered into greenish to yellowish chlorite; at least,
transitions seem to be obvious. D 12536 contains several pyroxenes, which are intergrown (! ?)

with hornblende individuals (the different hornblende parts in the pyroxene have one and
the same extinction). The latter hornblende too is here and there chloritized; even strongh'
chloritized hornblendes occur in intergrowth with little pyroxene.

Magnetite and titanomagnetite are present in a varying quantity; the titanomagnetite
crystals show leucoxene flocks or titanite rims. The very big grains and skeleton-shaped
grains lie allotriomorphically between the plagioclase laths and prisms. - Apatite has been
only found in some diabases, as small needles and prisms. - Only a few rocks contain numer-
ous diminutive grains or less, bigger grains of a mineral, which seems to be titanite (second-
ary?).

Quartz: Quartz is only present in part of the diabases described here. It seems to
belong to the magmatic crystallization-sequence in the diabases D 12535, D 12536, D 12537,
D 12542, D 12543 and D 12546. Their quartz occurs in larger or smaller amount and allo-
triomorphically between the plagioclase laths; the plagioclases in D 12536, D 12542 and
D 12543 are here and there in intergrowth with it. It is not or slightly undulose and contains
but here and there fluid-inclusions, partly arranged in planes. - The quartz is of a secondary
origin in the diabases D 12539 and D 12541 and replaced partly or wholly the plagioclase
crystals (see above). - It is problematical whether the quartz in D 12534 and D 12547 is
primary or secondary. It is interstitial between the plagioclase laths, and occurs as a very
finegrained, rarely coarser grained, aggregate. The grains of this aggregate seem to be cata-
clastic; in D 12547, they contain diminutive hornblende needles.

In some of the diabases veins occur. D 12538, for instance, contains narrow veins of
chlorite-plagioclase and of epidote. D 12534 shows a narrow quartz vein.

W. of Dos Playa and between Dos Playa and Rooi Fluit: A 470 - D 12534; A 471 -
D 12535; A 472 - D 12536; A 484 - D 12548; A 485 - D 12549. W. of Boca Prins and between
Boca Prins and Dos Playa: A 474 - D 12538; A 475 - D 12539; A 477 - D 12541; A 478 -
D 12542; A 479 - D 12543. Near Quadirikiri (E-coast): A 482 - D 12546. E. of Arikok and
Arikok: A 473 - D 12537; A 480 - D 12544. S. of Kleine Jamanota: A 476 - D 12540. Noord-
kaap: A 483 - D 12547.

Since both kinds of rock differ only in some points and are on the whole the same, it
seems better to unite them in one description; the points of distinction will be lifted out.
where necessary.

Macroscopically these rocks are similar to the diabases. It is remarkable, that most of the
common uralite-diabascs are mediumgrained, whereas most of the contact-uralite-diabases
are finegrained.

Microscopic description: Many of the diabases have a normally ophitic texture. Others
are ophitic to hypidiomorphic-granulose-gabbroic or gabbroic: uralite-gabbrodiabases and
contact-uralite-gabbrodiabases; a great deal of them have been sampled in the mountains
E and NE of Spaansch Lagoen. The texture of another part of the contact-diabases is partly
or quite deteriorated, so that only here and there the original texture can be recognized.
The plagioclase crystals, defining the diabase-texture, have been partly or quite changed
into a finegrained plagioclase aggregate: D 12554, D 12574, D 12578, D 12585, D 12590,
D 12598. The rocks with this kind of texture occur all very near the contact; however,
others which have also been sampled near the contact do not possess it (see the finding-
places).

The rocks consist mainly of plagioclase and uralite-hornblende. There may be less
or more uralite than plagioclase. On the whole, the gabbroic types and the ophitic contact-
diabases contain more plagioclase than the normal, ophitic ones. Some rocks contain moreover
some quartz of primary or secondary character. D 6176 has a flow-structure.

Plagioclase: On the whole, the plagioclase crystals occur in the same way as in the
diabases. It can be remarked that bytownite and labrador-bytownite occur only in the
contact-diabases. The crystals in D 12578, D 12582 and D 12584 contain diminutive, grainy
inclusions (fluid-inclusions?); those of D 12557, D 12558 and D 12562 (mountains E and
NE of Spaansch Lagoen) contain grayish or brownish spots, which are accumulations of
diminutive, rod- or plate-shaped microlites.

Uralite-homblende: The uralite-homblende is about the same as that of the diabases;
it is rarely brownish-green. Most of the gabbroic diabases and also some ophitic ones contain
beside the allotriomorphic crystals uralite-homblendes which, having originated from pyroxene
prisms, are more or less prism-shaped. The uralite-homblende of most of the normal and
contact-diabases is fibrous, non-fibrous, or granular. Only fibrous uralite can be found in
the normal diabases D 12553 and D 12567. The strongly contactmetamorphic diabases D 6176,
D 12572, D 12574, D 12578, D 12579, D 12585 and D 12590 contain only nonfibrous horn-
blende. The latter, allotriomorphic, locally undulose and known already from the diabases,
represents very probably the final stage of uralitization; at least, in the rocks D 12557,
D 12558, D 12562 and D 12563 (mountains NE and E of Spaansch Lagoen) such hornblende
crystals occur with hornblende-cleavage and pyroxene-shape (fig. 2). Separate needles or
radial bundles of small hornblende needles stick in the plagioclase, whereas numerous needles,
prisms and grains lie enclosed in the plagioclase. In some rocks the uralite has been altered
into chlorite for a small part; the chloritization begins along cleavage-planes and fissures.
The chloritization is not specially connected with the contactmetamorphism.

The essential contact-phenomenon in the contact-uralite-diabases is the occurrence
of small, typically idiomorphic and well-cleaved (hornblende-cleavage) hornblende crystals
(fig. 3). They occur in a greater or smaller quantity, dependent on the grade of contact-
metamorphism, and especially in the bigger uralite-homblende individuals. They must have
been new-made out of the uralite-material, under the influence of the contactmetamorphic
action of the diorite intrusion.

Hornblende individuals with enclosed bubbles of Pquartz occur in the contact-rocks
D 6549, D 12572, D 12578, D 12579, D 12590 and D 12598. Most of these rocks contain
'quartz or quartz-veins; hence, there seems to be a connection between this quartz and the
occurrence of quartz-bubbles, although other contact-diabases with quartz lack quartz-
bubbles in the hornblende. Especially some hornblendes in D 12579 contain big quartz !-
bubbles and are rich in quartz. The quartz must have been impregnated into the new-made
hornblendes (homblende-myrmekite; see also p. 95). — In D 6557 some of the pyroxenes
have been changed into uralite and a very finegrained Pquartz aggregate.

Pyroxene, being almost-colourless diopsidic augite, occurs as cores here and there in
the uralite of the normal rock D 12553 (east-slope of Jamanota) and of the contact-rock
D 12584. Remnants of the same pyroxene also occur in the well-cleaved, allotriomorphic
uralite-homblende of the contact-rocks D 6557, D 12571. D 12572, D 12583 and D 12585
(Seroe Pretoe, N of Savaneta and NW of Shete). Hence, it is clear, that there is no sharp
difference between the diabase and uralite-diabase.

Apatite occurs in several rocks; especially in the plagioclase. Magnetite and titano-
magnetite occur as in the diabases. The greater part of the ore is tied to the uralite-hom-
blende. In the contact-diabases of the contactzone D 12561, D 12578, D 12582, D 12583,
D 12584, D 12585 and D 12590 the titanomagnetite, locally with epidote and titanite,
has been concentrated into grainy groups, in consequence of the contactmetamorphism
(fig. 4). Primary or secondary titanite occurs in a few rocks as grainy masses.

Quartz: Many of the normal uralite-diabases and some contact-uralite-diabases
contain quartz. In the normal diabases D 12555, D 12556 and D 12565 and the contact-
diabases D 12562 and D 12579 it seems to be primary, and occurs interstitially and in a very
small amount. The plagioclases are only partly idiomorphic with regard to the quartz;
for the other part their borders are intergrown with it (D 12556, irregularly granophyric
intergrowth). Homblende needles of the uralite stick in the quartz. - The rock no. 3287 -
D 2339 in the Delft coUection (pebble from Rooi Taki, E of Spaansch Lagoen) is a normal

quartz-bearing uralite-gabbro-diabase, the quartz of which is primary and interstitial.
Besides, however, quartz and plagioclase constitute a fine granophyric-micrographic inter-
growth, in which the plagioclase, with the composition of about oligoclase-andesine, has the
same orientation as the nearest big plagioclase crystal or as its most peripheric zone. So,
the quartz and the rather acid plagioclase restmaterial must have crystallized after the
crystallization of the bulk of the plagioclase material (fig. 5). - The quartz amount in the
rocks D 12563 and D 12590 is extremely small. The quartz is probably of a secondary
character in D 6549 and D 12553: rather much quartz in very finegrained aggregates be-
tween the plagioclase laths.

Many rocks contain epidote-zoisite grains or narrow epidote-zoisite-veins, the latter
with or without quartz. D 12565, D 12567 and D 12579 are rather strongly epidotized, so
that here and there the epidote replaced the plagioclase. - D 6549 contains, in the close
neighbourhood of hornblende, diminutive plates of probably secondary biotite. - D 6176
contains a vein of quartz, some epidote and hornblende. - D 12579 contains a quartz-
plagioclase-vein that gradually merges into the contact-diabase. The plagioclases are pris-'
matic and bent albites; the quartz is intergrown with their borders. The plagioclase of the
uralite-diabase itself is also albite. - A vein in D 12588 also gradually merges into the contact-
diabase, and consists of a grainy aggregate of albites with some quartz, epidote, magnetite
and small hornblende needles, the latter at the borders of the vein. - A vein in the contact-
diabase D 12598, also gradually merging, encloses diabase fragments. It consists mainly
of quartz, grainy bytownite and numerous diminutive hornblende prisms and grains; the
plagioclases contain numerous quartz drops (sieve-texture). It must be mentioned, that the
plagioclases of the invaded contact-diabase have the same basic composition, so that, it
would seem, the plagioclase and also the hornblende of the vein material belong to the dia-
base, whereas the quartz is added material, having been impregnated into the plagioclases.

These veins are clearly connected with the diorite intrusion into the older series, and
occur in the contactzone. The fact that the vein material in the latter three rocks is not
sharply bordered on the invaded rocks possibly means that the diabases have been partly
resorbed during the intrusion; probably, however, that the hornblendization (uralitization)
of the diabases was not quite finished at the time, when the quartz-plagioclase material
intruded (see also the discussion about the genesis of the uralite-diabase).

E of Spaansch Lagoen: A 494 - D 12558; A 498 - D 12562 (SW-foot of Seroe Largo);
A 499 - D 12563 (S of Seroe Largo). NE of Spaansch Lagoen: A 491 - D 12555; A 492 -
D 12556; A 493 - D 12557. N of Spaansch Lagoen: A 490 - D 12554. Mira la Mar: A 565 -
D 12588. NW of Arikok: A 583 - D 12598. NW of Shete: A 556 - D 12582; A 557 - D 12583;
A 558 - D 12584; A 559 - D 12585. Sabanilla Abau (SE of Santa Lucia): A 564 - D 12587.

Near the coast of Andicouri: P 85 - D 6549. S of Noordkaap: A 503 - D 12567. Daimari:
A 501 - D 12565. E-slope of Jamanota: A 489 - D 12553. Near Baranca Corra: A 551 -
D 12578; A 552 - D 12579. Seroe Pretoe (N of Savaneta): P 96 - D 6557; A 507 - D 12571;
A 508 - D 12572. Near Rincon (E-coast): A 497 - D 12561. Between Rincon and Fontein:
P 97 - D 6176. S of Tibusji (NW): A 567 - D 12590. NW of Annaboei (NW): A 547 - D 12574. i)

Professor J. A. Grutterink sampled, amongst others, contactmetamorphic uralite-
diabases on the Seroe Crystall and on the southeastern slope of the hill E of Malmok (NW-
Aruba), amidst other contact-rocks. - The rock on the Seroe Crystall (no. 3356 - D 2408)
still contains rare pyroxene remnants. - The hornblende of the rock no. 3395 - D 2445,
on the hill E of Malmok, is present as non-fibrous, well-cleaved uralite with a good deal of
unaltered pyroxene, and moreover as many new-made crystals; the latter occur here and
there in aggregates, which lie allotriomorphically between the plagioclases. - The plagioclase
of the rock no. 3396 - D 2446 from the same finding-place has been locally altered into a
grainy aggregate. Its hornblende occurs as in D 2445, and also in aggregates together with
the grainy plagioclase.

It is a remarkable fact, that in these three rocks and also in the contact-diabases of
the Seroe Pretoe (N of Savaneta), and of the contactzone NW of Shete (see above) unaltered
pyroxene still occurs, although these rocks have been sampled very near the contact with
the diorite; whereas in other contact-diabases the pyroxene can no more be found. The
cause of the partial preservation of the pyroxene may be looked for in a quick and strong
contactmetamorphism, so that the already-made uralite of the diabase could change into
contact-hornblende, whereas the remaining pyroxene could find no time to alter into uralite
or hornblende. As we shall see later on, the uralitization of the diabases is very probably
connected with the intrusion of the diorite batholith.

If we compare the finding-places of the uralite-diabases with those of the contact-
metamorphic ones, it is very clear that the latter rocks chiefly occur in the close neigh-
' bourhood of the diorite contact and in the contactzone; whereas the normal uralite-diabases
occur iarther from the diorite. So, i. i. the samples taken just N of Spaansch Lagoen, on
Mira la Mar, NW of Arikok, NW of Shete, on Sabanilla Abau, near the coast of Andicouri,
near Baranca Corra, on the Seroe Pretoe (N of Savaneta), near Rincon, on the Seroe Crystall,
on the hill E of Malmok (NW), S of Tibusji (NW), and NW of Annaboei (NW) are all contact-
metamorphic diabases. One contactmetamorphic rock has been sampled on the SW-foot
of Seroe Largo (E of Spaansch Lagoen), apparently far from the batholith; probably, however,
the diorite lies not so very deep here in the underground (see also the distribution of the
contactmetamorphic hornblende-schists).

Beside the normal diabases, aphanitic to very finegrained, porphyritic rocks have been
collected, that are, moreover, a little aberrant.

So f. i. the rock A 495 - D 12559, which occurs very near and NW of Boca Prins.
The rock contains small nests of quartz. Small phenocrysts lie in a very fine-textured

1) J. H. Kloos (25) described some normally ophitic diabases and uralite-diabases.
Abusively he reckoned the vintlite 120c among the urahte-diabases. The uralite-diabases
111 and 113 of Mira la Mar are contactmetamorphic, especially 111, although Kloos ascribes
the hornblendes a „Mangel eigener krystallographischer Begrenzung - Nevertheless, he
observed, „dass hier die- Amphibolmikrolithe auch m die primären l^eidspathleisten ein-
dringen und Letztere ganz mit grünen Nädelchen durchspickt werden. Man kann diese
quot;Erscheinung nicht anders deuten als dass hier eine angehende Pseudomorphose von «om-
quot;blende nach Feldspath vorliegt, in vollständiger Uebereinstimmung mit den Erscheinungen,
quot;die in Diabasen beobachtet worden sind, wo solche in einer Contactzone von später empor-
quot;gedrungenen Eruptivmassen angetroffen werden.'

groundmass. The latter consists of an aggregate of radial-fibrous pyroxene, with numberless
diminutive pyroxene needles and also plagioclase needles. The phenocrysts are plagioclases
and pyroxenes. The former are lath- and needle-shaped crystals of an average com-
position; some of them show twinning. The pyroxenes are well-idiomorphic prisms of a
colourless monoclinic pyroxene, a single of which shows twinning. Several veins and irreg-
ularly shaped nests contain dusty quartz, chlorite and epidote; rarely Pprehnite.

Another rock, A 506 - D 12570, has been sampled in Rooi Dwars, near Boca Prins
(with an inclusion of altered tuff). It has been invaded by calcite. A few small phenocrysts
lie in a fine-textured groundmass. The groundmass consists of very small and twinned
plagioclase laths and needles, between which numerous pyroxene grains, small chlorite
masses and very small calcite grains occur. A part of the rock is a little coarser grained
and shows plagioclase needles which diverge in imperfect bundles. A few magnetites and a
single pyrite are accessory. The phenocrysts are plagioclases and pyroxenes. The former
lie partly in groups, and are partly idiomorphic, prismatic crystals, probably of an acid
composition. The pyroxene phenocrysts are small prisms and grains of a colourless mono-
clinic pyroxene. A small fragment of ophitic diabase occurs enclosed. Small cavities are
filled with radial-fibrous chlorite and/or calcite.

A 481 - D 12545 (Quadirikiri) contains a few phenocrj'sts of plagioclase and pyroxene.
The plagioclase laths and needles of the groundmass are rather short and lie in sheaflike
bundles. The pyroxene lies as grains bet^veen these plagioclases. The rock has been invaded
by quartz-epidote.

Beside the normal uralite-diabases, aphanitic to very finegrained and partly porphyritic
rocks have been sampled, which are a little different from the others.

A 505 - D 12569, collected S of Andicouri, contains some small phenocrysts in an
ophitic groundmass. The plagioclase occurs as small, twinned laths of about oligoclase-
andesine. The laths show a tendency to lie in imperfectly divergent bundles. The hornblende
is fibrous. The phenocrysts are plagioclases and diopsides. The former lie here and there
in groups and are twinned laths of an average composition. The pyroxenes are almost
colourless grains and prisms, uralitized along borders and fissures.

A 502 - D 12566, near Daimari, is extremely finegrained. An ophitic texture can be
recognized with difficulty. The plagioclases of the groundmass are very tiny laths which
may show a tendency to lie in imperfectly divergent bundles; the uralite is parallel- or
radial-fibrous. Magnetite is rare. The few phenocrysts are prismatic plagioclases and parallel-
fibrous uralite-hornblendes. The diabase has been strongly invaded by narrow veins, which
are rather sharply bordered but yet merge into the diabase; they consist of grainy albite,
with some epidote and chlorite.

A 500 - D 12564, from the Jamanota, contains amygdules. The groundmass consists
of an aggregate of radial-fibrous and plumy uralite-homblende with here and there dimin-
utive plagioclase needles. The phenocrysts are plagioclases and hornblendes. The former
are small prisms and needles; quartz aggregates replaced some of them with preservation
of the crystalform. The hornblendes are pale-green, short-prismatic, partly chloritized and
Pepidotized. There arc epidote-quartz-veins. The amygdules are composed of quartz,
•'prehnite, epidote and calcite.

The rocks A 487 - D 12551 (near Seroe Blanco, SE - Aruba), A 488 - D 12552 (upper course
Rooi Prins, near Juditi), A 496 - D 12560 (du Chef) and A 504 - D 12568 (on the top of the
hill between Andicouri and Daimari) contain more uralite than plagioclase. The plagioclase
laths and needles, twinned and here and there bent, lie in imperfectly divergent bundles
and are of an average composition. The fibrous uralite lies between the plagioclases in these
bundles and shows therefore a plumy character. In general, it also lies partly in the plagio-
clases, so that it partly replaced the latter. In D 12552 and D 12560 the uralite is partly
chloritized. The latter rock still contains pyroxene. Magnetite is rare. D 12552 contains

been quite uralitized. ^^e rocks A.02 ^ ^nbsp;divergeerenquot;
of the ..Dichte ^^^^^L be wholly compared with the

(Molengraaff, p. 31). A 506 ^^^ ,nbsp;described together, can be altogether
ktter kind of Curasao diabases. The iour ^^^^Ln uralitized totally or

As we have seen these two kinds of rock are not fundamentally different^
that is to say, in some region between Boca Keto^Jnd.t^^^^^^nbsp;^^ ^^^^

the rocks found outside the above-mentioned region show a strong alteration
and are consequently transitional types between diabase and urahte-diabase.
Diabases have been found in the outcrop SE of Fontein too; those sampled near
Quadirikiri are but little altered. At all events, the diabases are wanting in those
parts of the older formation, which lie along the batholith, and occur chiefly
in a region farthermost from the batholith; uralite-diabases are just wanting
in the latter region.

The uralitization of the diabase may be connected with the strong folding
of the older formation. Since, however, we can admit that the whole, older com-
plex has been subdued to orogenic movements, it is hard to understand why in
some places, in this case the above-mentioned region, the total uralitization did
not come off. Therefore, if we take into consideration the special distribution of
diabases and uralite-diabases, we must come to the conclusion that the process
of urahtization is closely connected with the bathoHthic intrusion of the dioritic
magma. Hence, this process of total uralitization is a kind of contactmetamor-
phism, which acted over a distance of about 2 km, that is to say, irom the visible
contact. As we have seen on p. 15 quartz-plagioclase material, connected with
the intrusion, seems to have intruded into uralite-diabases before the uralitization
was quite finished. This also points to this conclusion. - As we have seen above
and as we shall see below, those uralite-diabases which lie near or in the contact-
zone have been submitted to the strongest contactmetamorphism. Locally in
the diabase-region W of Boca Prins uralitized diabases occur in the narrow
contactzone of diorite- and porphyrite-dikes, f.i. A 539 which is invaded by
narrow veins. On the other hand, the partial alteration of the rocks in this region
IS in many cases not visibly connected with the intrusion of a dike-rock but must
be a slight effect of the batholithic intrusion, which had more influence in the
rocks nearer the contact. At all events, the several dikes and veins here do not
point to a close neighbourhood of the batholith in the underground.

The schistose and tuffoid rocks show similar relations to the diorite, which
will be discussed below. - It.must be mentioned that already Martin and especial-
ly Kloos suspected that the uralitization had something to do with the intrusion,
although they had not the disposal of many observations. Martin (30, p. 50)
remarked: quot;Bekannt ist das Vorkommen der uralitisirten Diabase von Miralamar
quot;sowie von Chetta am Fuss des Arikok, in beiden Fällen also von Punkten,
quot;welche in der nächsten Nähe der Formationsgrenze von Diabas und Diorit
quot;gelegen sind. Dagegen sind die Diabase, welche ich am Nordstrande geschlagen
quot;habe, nicht metamorphosirt.quot; And Kloos (25, p. 61), taking into consideration
the younger age of the bathohth, remarked, quot;dass es dadurch den Anschein ge-
quot;winnt, als läge in den Grünschiefern und Uralitdiabasen Arubas das Beispiel
quot;einer Contactzone eines Dioritmassivs vor, welche in vieler Beziehung mit
quot;bekannten Contacthöfen um granitische Gesteine übereinstimmt.quot;

The diabases occur in the landscape more or less alternatively with the other
rocks of the older formation. They can be generally distinguished from these
other rocks by their brownish to reddish-brown colour of weathermg and often
by the roundish shape of the diabase hills. In a few places, however the difference
is not very clear because of a more or less schisty character o the diabases.
Nevertheless, such a schistosity is not visible microscopically. Where the rocks
crop out they are covered with mountain waste, here and there m large masses.

The diabasic rocks occur mainly in the large outcrop of the older formation
inthecentralpart of the island. Besides, they have been found in the o^crop SE
of Fontein and in that NW of Rincon. Very small outcrops he about half a kilo^
meter NE of Seroe Blanco (SE) in the diorite, on the top of the Seroe Pretoe N
of Savaneta, on the top of the Seroe Crystall, in the conta^zone E of Plantation
Westpunt (NW). on the top of the hill just E of Malmok (NW), on the top 27.80
(NW) - Big and round diabase blocks belonging to the outcrop of the hill E of
Malmok occur far from this outcrop, that is to say along the slopes, and ]ust
W of the house of Westpunt.

Schistose and tuffoid rocks are widespread in the older formation. As will
be shown transitional types between these kinds of rocks are also Present m
the island and prove that the former originated from tuffoid rocks, very probably
under influence of the diorite intrusion. The schistose character of these metamor-
phic tuffs is mainly connected with hornblendization. Therefore, most of the
schistose rocks are hornblende-schists; locally also chlorite and epidote are the
main constituent minerals. Moreover, there will be described tuffoid rocks which
have been little or not hornblendized. The tuffoid rocks are very probably diabase-
tuffs. In a few places curious, schisty, porphyritic rocks have been sampled.

The following kinds of rock will be described: hornblende-schists without
tuff relic-minerals; hornblende-schists which are clearly metamorphic diabase-
tuffs; the same ones strongly invaded; hornblende-chlorite-schists; hornblende-

HORNBLBNDE-SCHISTS s. str.: The rocks a 629 - d 12629 and a 633 - d 12633 are true
hornblLde-schists, that is to say, they consist almost totally of hornblende wherea u
relic-minerals cannot be found. Hence, it is questionable whether these rocks have a tuffotd

a 629 - d 12629 is a greeny and schisty rock, sampled n of Spaansch Lagoen It
.howt a kind of banded structure: parallel layers and stretched lenses of hornblende-sdnst

and vein materiail alternate in a more or less regular way; the two types of rock merge abruot-
ly. The structure of the hornblende-schist is roughly parallel. The texture is about nemato-
blastic to fibroblastic. Here and there some plagioclase occurs. Small magnetite grains arc
rare, and occur in the vein material too. Brownish and small flocks may be leucoxene. The
hornblende is present as bigger crystals, and as a more fibrous aggregate between the latter.
They are green, prismatic, sound-bordered crystals, here and there idiomorphic; cleavage is
developed, several of the crystals are twinned, whereas a few column-shaped ones are bent.
The quot;veinsquot; consist of a granular aggregate of albite to oligoclase, with numberless small
hornblende needles, prisms and grains; the latter lie very roughly parallel. Here and there
a little epidote and sericite can be seen. A true vein consists of epidote-zoisite, some quartz,
albite and chlorite. As to the nature of the plagioclase layers and of the veins, see p. 24.

A 633 - D 12633 is a blackgreenish and finegrained hornblende-schist in contact with
quartz-epidote -veins, sampled S of Seroe Blanco, near Spaansch Lagoen. The schist merges
into the epidote-quartz-rock rather abruptly. The hornblende-schist is a diverse aggregate
of rather big, short-prismatic and non-idiomorphic hornblende crystals. The latter are gener-
ally palegreen, terminally frayed, fibrous, here and there bent; some of them are well-
cleaved, a few crystals are twinned, and here and there the hornblende is partly chloritized.
Grainy zoisite-epidote and a very little plagioclase occur between the hornblendes. Besides,
many grains and masses of titanite are present. The epidote-quartz-vein contains several
titanite grains, as in the schist. In several places we see great masses of enclosed hornblende
fibres, many of which have been chloritized; these hornblende fibres may have originally
belonged to the hornblendeschist and may have been taken up by the epidote-quartz-liquid.

The hornblende-schist A 671 - D 12671 joins the other ones, but contains rather much
chlorite (S of Seroe Largo). In a tangly aggregate of very lightgreen to almost colourless,
fibrous hornblende crystals, between which a great amount of very palegreen, almost isotrop-
ic chlorite occurs, lie several big hornblende individuals. Amongst the smaller hornblendes
many crystals occur, which have a pood prism-shape and the characteristic hornblende-
cleavage. The big hornblendes too are very lightgreen, not clearly prismatic, frayed and in
part fibrous; a single one shows twinning. Several of these hornblendes are partly chloritizcd,
in such a way that the hornblende material occurs as round spots in the centre of the chlorite.
A very little plagioclase may be present here and there. Magnetite is abundant.quot;

Hornblende -schists (metamorphic Diabase-tukfs) s. Str.; Although the name horn-
blende-schist seems to be a little exaggerated for these rocks, which on the whole do not
give the impression of being rather strongly metamorphic, this name can be used here accord-
ing to H. Rosenbusch (37, p. 701), who wrote about this kind of rocks: quot;Die Textur der
■'Hornblendeschiefer ist mehr oder weniger deutlich schiefrig, wobei innerhalb der Schiefe-
quot;rungsfläche die einzelnen Amphibolsäulchen bald richtungslos, öfter mehr oder, weniger
quot;parallel und nicht selten recht streng parallel liegen. Die Gesteine sehen dann gestreckt aus
quot;und haben bei hinreichend feinem Korn oft den Seidenglanz gewisser gefalteter Phyllitc
quot;und Tonschiefer.quot; As we shall see below the structure of the rocks described here agrees
with that, described by Rosenbusch. On the other hand, the presence of a little plagioclase
and of the relic-minerals plagioclase and hornblende, and the general geological and pétro-
graphie relations prove that we have not to deal with true hornblende-schists, as they have
been described by Rosenbusch and Grubenmann f.i., but with not very strongly metamor-
phic tuffs. Therefore, the name quot;metamorphic diabase-tuffsquot; has been added, to indicate
more or less the nature of these hornblende-schists.

Macroscopic description: The rocks arc light- to darkcolourcd, greenish to grayish,
rarely black. Far the most of the greeny rocks and only part of the gray ones are more or less
foliaceous (schisty). Several greeny rocks are. besides foliaceous, somewhat lustrous on the
cleavage-planes (schist-planes). Some of the schisty rocks have a platy cleavage. On the whole
these rocks arc aphanitic. Rarely separate hornblendes can be distinguished. - A 650, A 661.
A 664, A 678 and A 680 are similar; however, non-schistose.

true diverse-fibrous hornblende felt. The four ^^Jcroscopically schisty rocks. The sections
without schistosity; the three latter, ^-e^^^nbsp;^St the separate horn-

schistose rocks D 12630. D 12631. JJ i^^o „„„^le^gtructured hornblende aggregate: m

of them parallel, for the others massive. ^^^^nbsp;^ ^^^^^^ ^ ^^ ^^635. D 12677) the
In some

also have come into existence ^^^rfé loc^Ts^ents in tL metamorphic tuffs have not
rock-fragments. In any case, unaltered rocK i^agme inbsp;f ^he matrix of the non-

hornblende felt changes from place J^«nbsp;^ jy 12657, the matrix of hornblende

plagioclase is questionable. Maybe it « ^^^^^^nbsp;.^e invasion of vein material

contains, beside the plagioclase. an isotropic substanc^^^^nbsp;plagioclase. but regulariy

is very rich in epidote and can be call^ j;^°tstrTngs and are locally accumulated in
grains in the matrix of D 12636 he P-^Yo^^^^^^nbsp;^^^

lie without order in the matrix; except in D 12631, in which the prism-shaped crystals are
rather parallel to the schistosity. Hence, in general, the process of metamorphism had
no influence on the situation of the bigger tuff-crystals.

The plagioclase crystals are idiomorphic or non-idiomorphic, short-prismatic crystals
or only fragments of crystals (compare with tuffs), rarely with rounded-off edges. They
partly show lamelling; simply zonal plagioclases can be seen in a few rocks. In general, the
composition is an average or rather acid one; some of the crystals could be determined as
andesine and oligoclase-andesine. The crystals are fresh, rarely sericitized or partly albitized.
In some rocks the diminutive hornblende needles of the matrix stick in the plagioclase or
seem to stick in it; if they really do, this proves that even the plagioclase relic-minerals were
somewhat subdued to the process of metamorphism.

The hornblende crystals are pale-green, non-idiomorphic, short-prismatic, terminally
frayed; most of them in most of the rocks are parallel-fibrous and here and there bent, the
others are non-fibrous; some are twinned. The hornblendes are generally unaltered; only
a single one has been partly chloritized. A number of hornblendes in D 12630 are needle-
shaped with frayed ends; probably, these hornblendes indicate the beginning of a stronger
contactmetamorphism (see the general remarks, and the description of the contactmetamor-
phic hornblende-schists). This rock has been sampled N of Spaansch Lagoen and near the
contact with diorite. — The hornblendes very probably are uralite crystals, that is to say
uralitized pyroxenes; unaltered pyroxenes have not been found.

Both plagioclase and uralite crystals can be considered as relic-minerals, which were
the bigger crystals and crystal-fragments in diabase tuffs. Probably, they originated
from diabase magmas. The plagioclases have been more or less albitized and have a more
acid composition than diabase plagioclases. The pyroxenes have been uralitized, very
probably, during the process of metamorphism of the tuffs (compare with the unaltered tuff
A 646—D 12646 on p. 28).

A single quartz crystalgrain in D 12648 may be a diabase mineral as well, or is foreign
material. - Problematic remnants of Radiolaria can be seen in D 12657 and D 12680. -
A few small and parallel-stretched quartz nests occur in D 12648. Small aggregates of dimin-
utive biotite plates, with limonite. in D 12677, and a single biotite in D 12648 may be
new-made.

Most of the rocks have been invaded by veins. This invasion of hydrothermal and more oi
less magmatic solutions must have been connected with the diorite intrusion. It is significant,
that the rocks, sampled N of the line Mira la Mar—Rooi Prins, contain no veins, whereas
far the most of those occurring S of this line, are more or less invaded. The veinminerals are
epidote, quartz, plagioclase, chlorite, ore and ?prehmte. The veins are rather sharply bordered
on the matrix; fragments of the latter may occur enclosed; or matrix and vein merge.
As to the rock D 12650, the process of hornblendization has probably proceeded even
after the intrusion, for the liomblende needles stick in the plagioclase-vein; the intruding
liquid however may also have loosened the matrix hornblendes.

Hill S of Jamanota: P 88-D6551. Seroe Blanco (near Spaansch Lagoen): A636 —
D 12636; A 637-D 12637. E of Spaansch Lagoen: A 634—D 12634; A 635-D 12635;
P 87—D 6174. NE of Spaansch Lagoen: A 631—D 12631. N of Spaansch Lagoen: A 630—
D 12630. Mira la Mar: P 78—D 6544. N of Mira la Mar: A 648—D 12648. S of Andicouri:
A 677- D 12677; A 678—D 12678. W of Dos Playa: A 680—D 12680. Upper course of Rooi
Prins near Juditi: A 657—D 12657. SE of Gran Tonel: A 650—D 12650. S-foot of Gran
Tonei: a 651—D 12651. Just N of Baranca Corra: A661—D 12661; A 664—D 12664. i)

1) Martin 96 sampled in the quot;rooiquot; N of Spaansch Lagoen, has been described by
J. H. Kloos (25, p 47). Kloos did not describe the plagioclase and hornblende tuff-crystalls
and did not recognize the rock as a metamorphic tuff.

.ecus are uot much — from tUe otUer metamorpUic tuffs. Ouly the strong mvas.on of

consists for the greater part of a diverse no , ,nbsp;, r^-u^ matrix is present as irregu-

rock-material: metamorphic '-l^iZ^'^iTl^ers of vein-material occur. The two kinds
plicated tuff layers, bet^veen which only a few layers

The metamorphic-tuff layers consist of ^^^^^J^J^^c-min^^^^ of plagioclase and
blende aggregate with a varying denseness, and with a few relicnbsp;^^i^.^^aterial partly

chlorite and many epidote grams; part of the ^^^^^^ ^2632 are rather basic and look

with a varying denseness. In this ag^egate the fonbsp;^^^^ distribution of which

are not sharply bordered on interjacent masses of fibrous chlorite with steelblue inter-
ference-colours. In this chlorite also numerous hornblende fibres and needles occur, while
here and there the transition between hornblende and chlorite is clear. The hornblende
lenses are a little brown-coloured, probably by limonite; the chlorite is lightgreen: hence the
spotted appearance of the sample. Magnetite is rare. Numerous diminutive flocks are leuco-
xene or epidote. A few hornblende relic-minerals have an anygiven situation in the described
hornblende and chlorite masses. Some vein-like parts of the rock consist mainly of chlorite,
grainy quartz and leucoxene or epidote flocks, and also enclose parts of the hornblende
aggregate.

Hornblende-epidote-schist (metamorphic tuff): a 679—D 12679 (W of Dos Playa)
is an aphanitic, blackgrayish rock, with varioles. Microscopically it is a mass of rather
parallel and diminutive hornblende fibres, with numerous epidote grains, parallel-stretched
plagioclase nests and also some plagioclase fragments. This mass contains peculiar, small and
eggshaped elements, in which the hornblende fibres lie without order and which are a little
more transparent; • they are, however, not sharply bordered, and look like remnants of
Radiolaria. Several bigger (1 mm to 3 mm diameter), round to eggshaped elements are
similar, but contain moreover epidote grains and a few plagioclases. A typical connection
exists between these non-sharply bordered, round elements and the structure
of the rock (see fig. 6). The round elements must have behaved as rigid masses during the
dynamometamorphism. Magnetite is rare. Some epidote veins with a little chlorite and
limonite manifest a clear faulting in the rock. Two round elements also show faulted parts.

Martin 108, sampled in Rooi Prins, has been described by Kloos (25, p. 45f. It is a
hornblende-epidote-schist, strongly invaded by plagioclase.

These tuffs are less metamorphic than the hornblende-schists and represent the
transition forms between the latter and the hardly altered tuffoid rocks. The rocks will
be described according to decreasing metamorphism (hornblendization), as far as it is
possible to judge of the grade of metamorphism. They are aphanitic to finegrained, dark-
or lighter coloured; grayish, brownblue- or green-grayish.

A 655—D 12655 is the most metamorphic diabase-tuff and occurs westernmost of
these rocks: NE of Arikok. The main part of the rock consists of a very fine-structured
hornblende aggregate, with a little pyrite and magnetite. Bigger tuff-minerals, still preserved,
are plagioclases and hornblendes. The former are fragments and well-idiomorphic prisms,
lamelled and rather basic. The hornblende fragments are wholly or partly chloritized. Some
rock-fragments are uralite-diabase; others cannot be defined. It is questionable whether the
rock contains remnants of Radiolaria. This rock, occurring not so very far from the diorite.
contains an irregularly shaped vein of grainy plagioclase, with numerous fibrous hornblende
needles and prisms, and locally with zoisite, ore and titanite.

The rocks A 643—D 12643 and A 644—D 12644, sampled in the same place near Dos
Playa, are little metamorphic tuffoid rocks. A 643 is schisty-stratified. A 644 has no distinct
stratified structure. Both rocks contain numerous small ore- and limonite strings, which
determine the „stratified structurequot; in D 12643. The matrix takes up more room than the

bigger tutt-minerals. It looks very isotropic and very probably consists of a very fine-struc-
tured hornblende aggregate. Both rocks contain a great many small prisms and fragments
of plagioclase, partly lamelled, and here and there zonal; their composition is average or
rather basic (f.i. oligoclase-andesine, Plabrador). Crystals of uralite-hornblende are only
present in D 12644. Lens-shaped remnants of PRadiolaria can be seen in D 12643, and
D 12644 contains some very finegrained albite aggregates, here and there full of ore.

The rocks A 641—D 12641 and A 642—D 12642, being little metamorphic tuffs, have
been found in the same place, between Boca Prins and Dos Playa. A 641 is somewhat schisty
with brownish and blackish layers. A 642 is lustrous and schisty, with irregularly shaped
cavities, which are filled up with grayish-brownish, grainy and porous material. - D 12641
shows a stratified structure because of a difference in denseness; the less dense layers contain
moreover many limonite grains. The matrix of the more dense layers consists of parallel,
plicated and narrow layers of diminutive Phornblende fibres together with limonite and
diminutive plagioclase-like grains. The matrix of the less dense layers consists of an extremely
finegrained plagioclase-like aggregate, in which a great many extremely tiny Phornblende
fibres lie without any order; here and there the narrow Phornblende-layers with limonite,
as described above, occur. - D 12642 has a parallel-structured matrix, almost isotropic with
plagioclase-colours here and there, and with many diminutive hornblende fibres. - The
rocks contain similar plagioclases, uralite-hornblendes and filled PRadiolaria cavities as
A 643 and 644; moreover, a few quartzes. D 12642 contains big, irregularly shaped fragments
of other crystal-tuffs, richer in plagioclases (see the sample).

The rock A 665—D 12665, found near Boca Prins, is a tuffoid rock, somewhat epidotized
and hornblendized. The sample is grayish-purple and a little schisty. Many epidote grains
and many eggshaped or irregular masses of small dimensions, which consist of a very fine-
fibrous Phornblende felt, occur in an almost isotropic mass, which takes up only a very small
room and in which feldspar- and chlorite-colours can be seen. The masses of Phornblende felt
seem to contain some rests of PRadiolaria. The rock is full of ore. Bigger tuff-minerals are a
very few plagioclase and quartz fragments.

The rocks A 667—D 12667 and A 668—D 12668, sampled in the same place, about
2 km. W of Boca Prins, are little altered tuffs. The matrix is almost quite isotropic, but
probably contains diminutive hornblende fibres, which lie parallel in D 12668; moreover,
epidote grains. A great many plagioclases of average composition occur as bigger tuff-
crystals. Many uralite-hornblendes occur only in D 12667, while D 12668 contains egg-
shaped PRadiolaria cavities, filled with plagioclase and hornblende needles. Magnetite, a
little pyrite and limonite.

The rock A 669—D 12669, sampled SW of Dos Playa, is also a somewhat metamorphosed
and schisty tuff-rock. In a browny, isotropic-looking mass with diminutive hornblende fibres,
epidote grains, limonite grains and ore in small strings and groups, many small grains of
plagioclase, less of quartz, and uralite-hornblende prisms can be distinguished. A few small
rock-fragments cannot be determined. This rock, lying rather westward, contains a narrow
quartz-vein.

A 645—D 12645 is a PRadiolaria-bearing tuff, with only a beginning of metamorphism;
near Dos Playa. The rock contains calcite-amygdales. The differences in colour of the sample
are due to a difference in limonitization. The matrix is an aggregate mainly of average plagio-
clase and also of quartz, with moreover diminutive hornblende needles. It contains some
bigger, rather basic plagioclases, some of which are zonal. Several remnants of PRadiolaria;
their round or eggshaped to flat-eggshaped cavities have been filled with calcite. The latter
mineral also occurs scattered as very small grains.

Kloos (25) described on p. 48 the quot;Mergelschieferquot; of Dos Playa. It is a little hornblendi-
zed, calcite-bearing crystal-tuff with many plagioclase crystals and possibly with calcitized
PRadiolaria.

These tuffoid rocks only occur in the eastern regions of the older formation, that is to
say, in the region between Boca Ketoe, Juditi and Fontein. Most of the samples have even

been taken in the eastern part of this region, in about the triangular region between the
lower course of Rooi Prins and Dos Playa. Veins are as good as wanting in these rocks.

In connection with the metamorphic tuffoid rocks described here, the rock A 654—
D 12654, which has been found W of Dos Playa, can be described. It is a Variolitic tuff (?)
little metamorphic; — Macroscopic descriptionquot;. The varioles which are quot;herausprapariertquot;
at the brown-weathered surface show a clearly spheroidal construction. They have a diameter
of about 1 cm., and partly touch each other; here and there a bigger variole embraces a
smaller one (see fig. 7). The varioles are aphanitic and grayish, and their spheroidal forms can
be seen here and there in the fracture-planes. The interjacent rockmass takes up less room
than the varioles, and is finegrained and grayish. - Microscopic description. The varioles:
The spheroidal construction is manifested only by the fact, that a narrow peripheric border
is a little denser than the central parts. The varioles consist of an almost isotropic matrix,
with nuinerous diminutive ?hornblende fibres. In this matrix numerous crystals and crystal-
fragments can be seen: calcite, Pdiopside. Phornblende, plagioclase, epidote. Moreover,
there occur strange, brownish, ?organism-like elements and rather much pyrite. The inter-
jacent mass is a little coarser grained than the rock of the varioles. The latter are rather
sharply bordered on this mass. The same matrix and crystals as in the varioles occur here;
however, a little more calcite and epidote are present. Many roundish and angular-rounded-
off parts with a greater denseness, between which here and there chlorite, can be seen.

It is difficult to understand the genesis of this rock. Possibly, epigenetic concretions
came into existence in a muddy deposit, which contained much tuff-material. The inter-
jacent mass between these concretions has been replaced afterwards by coarser grained
tuff- and muddy material (the interjacent mass is a little coarser grained than the varioles,
and is rather sharply bordered on them). The rock has been diagenetically altered, and after
that also little metamorphosed (hornblende fibres). Probably, organic material was present
in the original deposit (calcite, pyrite, Porganisms). The matrix seems to have been a ?colloidal
amorphic mass. The replacement of the original interjacent mass seems to point to a sUght
change in level.

The little altered tuffoid rocks will be described first, the hardly altered ones after that.

The rocks A 683—D 12683 and A 684—D 12684 have been found in the outcrop SE
of Fontein. A 683—D 12683 is mainly a dark-purple rock with reddish-brown strings of
magnetite and limonite. Between these ore zones we see an isotropic, locally perhaps siliceous
matrix with diverse-fibrous ?talc (parallel extinction, zone, n = about 1,59), ore, Pleucoxene,
epidote and Pprehnite prisms. Bigger tuff-minerals are partly rounded-off plagioclase crystals
and fragments, and quartz grains. PRadiolaria. - A 684—D 12684 is a schisty, mainly purple-
rock; a great part of it is occupied by magnetite and limonite, while no unaltered matrix can
be seen. In the mass of ore a great many parallel-stretched, lense- and flat-lense-shaped
parts occur, composed of a very fine-structured, roughly-parallel-fibrous aggregate of Ptalc.
Besides, several round, roundish or angular quartzes and Radiolaria (! P) are present.

The little-altered crystal-tuff A 682—D 12682 (Rooi Prins, near Kasoenti) is a greenish-
gray, schisty rock, lustrous on the cleavage-planes. It is an accumulation of partly bent
albite prisms and fragments with titanomagnetite. cemented by chlorite with leucoxene.
Narrow veins of calcite consist of undulose individuals, which show here and tHere lamellar
twinning.

The rock A 674—D 12674, sampled on the northeastern slope of the Jamanota, is
schisty and purple-grayish. The matrix seems to be isotropic, but probably consists of a very
finegrained quartz aggregate, in which much magnetite occurs in small groups. These groups
are separated by zones, almost free of ore. Moreover, the matrix contains numerous epidote
grains, here and there brown, and also many roundish epidote aggregates, locally with
chlorite. As bigger tuff-crystals several quartzes and plagioclases are present.

The calcite-bearing tuff (?!) A 653-D 12653, W of Dos Playa, is aphanitic and bluish-
gray It IS an almost isotropic rock, consisting for a great part of small zoisite-like grains.
Calcite possibly secondary, occurs scattered through the rock. Moreover, some magnetite
limomte and. as tuff-minerals, some plagioclase fragments can be seen

The crystal-tuff A 681-D 12681 occurs as an inclusion in diabase of Rooi Dwars near
Koca Inns. The blackgrayish rock is an accumulation of small crystals, between which a
kind of cement occurs, grayish and flocky in reflected light. Most of the crystals are Pprehnite
which is probably pseudomorphic after plagioclase or pyroxene; the prehnite occurs as
tinegrained aggregates in prism-shape, here and there with quartz or chlorite. Several
crystals occurring as well-cleaved, colourless grains and prisms are probably monoclinic
pyroxenes. Also a few quartz fragments, remnants of PRadiolaria. and many pyrite grains
arc present. Narrow calcite-veins and widespread, grainy calcite.

D 1^646. In an almost isotropic matrix innumerable and very small mineral-fragments and
Jess remnants of PRadiolaria lie close together. Many small strings and grains of ore indicate
a parallel structure. Diminutive epidote or leucoxene grains are widespread. The small
crystal-fragments are partly-lamelled andesines and labradors. and less diopsidic augites

It IS noteworthy that the two latter rocks are the only ones of the little and non-hornblen-
aized tuffoid rocks which contain unaltered pyroxenes.

The rocks occur in about the same region as the partly hornblendized tuffs. Moreover
they have been found in the diabase and tuff region SE of Fontein. Only the rock A 674 lies
outside these regions, and has been sampled on the northeastern slope of the Jamanota in a
zone about 20 m. wide, lying in the midst of strongly metamorphic tuffs and other rocks
tieside a few calcite-veins in some of the rocks, they do not contain vein-material.

Appendix: Another rock, possibly also tuffoid. is A 640—D 12640, found near Boca
Prins. It is aphanitic. greenish-gray, and contains white nests. It consists of a finegrained
aggregate of radial-fibrous grains, with a very little magnetite, and locally with calcite
Several amygdaloid cavities are filled with: radial-fibrous Pprehnite, quartz calcite and
epidote. Fissures are filled with calcite, epidote and quartz. This rock may be an altered
amygdaloidal rock.

A266—D 12265 (Jamanota); A 780—D 13078 (Seroe Blanco, near Spaansch LaeoenV
A781—D 13079 (lower course Rooi Prins).nbsp;''

Macroscopically phenocrysts can be seen in a schisty and greeny groundmass. Microscop-
ically, the structure is parallel in consequence of flowing and moreover of dynamic pro-
cesses. The plagioclase phenocrysts are strongly altered, rounded-off albites. Hornblende
phenocrysts can be recognized only in D 12265; they are partly broken and are transitional
into strings of hornblende fibres, epidote and chlorite. Similar strings in the two other rocks,
together with sericite and leucoxene, may also have originated from hornblende. A single
round quartz phenocryst without a reactionrim occurs in D 13079. The groundmass of
D 12265 consists of albite laths, quartz and partly chloritized hornblende. In that of D 13079
the hornblende has been totally changed into stringy chlorite, biotite, sericite and leucoxene
The groundmass of D 13078 is banded by chlorite zones, rarely by quartz zones; it is a
quartz-plagioclase aggregate with numberless parallel hornblende needles and chlorite
A little ore and apatite are accessory. D 12265 has been invaded by quartz and albite!

Hence, these rocks have mainly a vintlitic character and might belong to the batholithic
rocks, except for their schistosity. Since porphyritic and vintlitic dikes without schistositv
and belonging to the diorite batholith occur in the older formation too, it is difficult to put
the latter and the former in one group of rocks. Therefore, these rocks have been described

under the schistose rocks of the older formation. However, since the diorite intrusion has
occurred during the folding of the older rocks, the possibility exists that locally the
porphyritic dikes have been subdued to the last phases of the folding, whereas in other places
similar dikes intruded after these phases had finished. - In our fieldnotes A 266 has been
indicated as an aberrant schist with a dike appearance, A 781 as lenses in schisty rocks, and
A 780 as a schist.

As we have seen above, the tuffoid rocks can be generally considered as
diabase-tuffs with bigger diabase-minerals. The quartzes in the tuffs may have
originated from diabase magma which crystallized here and there into quartz-
bearing diabases, but may also be of foreign origin (compare with the quartz-
sandstone A 656, and with the diabase-conglomerates). In the latter case the
tuffs with this foreign material are tuffites. - Some of the rocks contain remnants
of Radiolaria proving their deposition in a sea which was rather shallow, the quartz-
sandstone and the conglomerates, which can be probably considered as terrigenous
deposits, occurring alternatively with the tuffoid rocks (see also G. J. H. Molen-
GRAAFF (31) p. 21). The presence of the conglomerates points to non-submarine erup-
tions. The matrix of the tuffoid rocks, when not altered, is generally isotropic and
probably an amorphic (? colloidal) silicic acid. Possibly in many rocks this matrix
came into being in muddy and shallow water near the volcano (siHceous volcanic
mud). Radiolaria must have lived there. Other tuffoid rocks, however, may have
been deposited on land.

RELATION BETWEEN THE NOT AND LITTLE HORNBLENDIZED
TUFFOID ROCKS AND THE STRONGLY METAMORPHIC TUFFS (HORN-
BLENDE-SCHISTS S.L.), AND GENESIS OF THE LATTER.

If we compare the finding-places of these different rocks, it becomes clear
that the strongly metamorphic tuffs generally do not occur E of a line Boca
Ketoe-Juditi, whereas the bulk of the non-hornblendized and little hornblendizeji
tuffoid rocks can be found between this line and Fontein, and also in the outcrop
SE of Fontein. That is to say, the latter two kinds of rock occur farthermost
from the batholith; it is of significance, moreover, that the rock sampled western-
most (A 655, NE of Arikok) is the most metamorphic of them. So, it is very prob-
able that the metamorphism was due to the diorite intrusion, and besides to
the process of folding. The hornblendization must have been closely connected
with the intrusion, whereas the schistosity must have been the result of strong
orogenic movements in the older formation. The hornblendization can be com-
pared with the uralitization of the diabases. The metamorphism cannot be the
result only of the folding, for it would be incomprehensible then why certain
rocks have not been metamorphosed. So, the hornblende-schists s.l. are the
product of both dynamo- and contactmetamorphism; they show a clear schisto-
sity. The little hornblendized tuffs have been less subdued to contactmetamor-

Clear effects of contactmetamorphism; there is no schistosity in the latter rocks
Obviously, the folding of the older formation could only bring forth scWs quot;^
m the case of hornblendization of the tuffsnbsp;scnistosity

Tot Mi i!^ r connected with the intrusion are almost wanting in the
ess metamorphic and non-hornblendized tuffs. - As we have seen in some o

as that of contactmetamorphism, for the hornblende needles and fibres, resulting
from the contactmetamorphism, lie parallel in most of the hornblendized tuffc
Also the minute folding around epidote grains in some of the strongly invaded
hornblende-schists makes this probable, for the epidote must be conLcted w1 h

a folding process during the invasion of vein-material, the latter connected with

he d on e intrusion. So, we must come to the conclusion that t h e d i o r i t e

attention to the genesis of the quot;Grünschieferquot;, but called them
Tvenezuet and^^^^^^^^^^nbsp;hornblende-schists with the schists

„Analogie, welche die Inseln überhaupt zu dem Festlande in ihren geognostiscLn ^Sält

dTabases S Arubanbsp;'Snbsp;possibility that the hornblende-schists and uralite-

diabases of Aruba are quot;das Beispiel einer Contactzone eines Dioritmassivsquot; (p. 61).

In the landscape the schistose rocks can be distinguished from the diabases
because of their light colours and schistosity. The difference in appearance

aphamtic diabases is in many places rather small. Since the little and non-meta-
morphic tuffs do not show a clear schistosity the distinction between these rocks
and the hornblende-schists is always clear.

Both the schistose and tuffoid rocks show in most places a clear strike and
dip; that is to say, the former show strike and dip of the schistosity-planes, the
latter often those of the bedding-planes. The strikes which do not differ so much
from the E-W direction (N80E, N90E, NIOOE, N 110 E) largely prevail.
The average strike is about N 95 E.

Locally in the quot;rooiquot; on the SE-foot of the Jamanota the strike of the hornblende-
schists changes from W to E gradually from N 95 E into N 145 E, N 90 E, N 145 W and
back again to N 95 E; so, the schistosity-plane forms here a bending outwards towards the
south over a rather short distance. - Especially in the hills S of Andicouri and Noordkaap
aberrant strikes have been found f.i. N35, 45, 60, 125, 135E. - S of Seroe Blanco a malchite
dike N 135 E cuts across hornblende-schists, unconformably. It is remarkable that the
schists NE of the dike have a N90E strike and those SW of the dike a N105E strike. - Dips
towards the north and towards the south have been found in about the same number. Most
of the schistosity- and bedding-planes are vertical or very steep. Less steep dips have been
found too; they lie between 40° and 90°, many of them being about 50°.

The rocks only occur in the older formation between Spaansch Lagoen,
Andicouri and Fontein and in the outcrop SE of Fontein. — According to
Martin (30) they only occur in the W—E quot;rooienquot; Prins and Tamboe and also
in the E—^W quot;rooiquot; W of Rooi Prins. He considered them little resistant rocks
which have been eroded deeper than the surrounding and more resistant diabases.
Since the strike of the rocks is about E—W, these quot;rooienquot; must have got also
a somewhat E-W direction. Although the schistose and tuffoid rocks have a
much greater distribution, the idea of Martin about genesis and direction of
these quot;rooienquot; must be right. Other quot;rooienquot; in which we found the same rocks
show these properties too. However, the rocks do not occur only in quot;rooienquot; but
are also present on the slopes and the tops of the mountains. Since the schists are
the principal rocks in the southern mountains they must occur here, besides in
the valleys, on the slopes and the tops. So f.i. the Seroe Blanco, Seroe Cucu, Seroe
Largo and Kleine Jamanota mainly consist of schists. On the other hand, in the
central and northern parts of the formation where the diabase is more widespread,
the different mountains and the tops, f.i. the Seroe Kabaai and Du Chef, Mira
la Mar, Seroe Boonchi and Arikok consist for the greater part of diabase, whereas
in these regions the schists and tuffs have been more eroded and form the valleys,
generally.

The quot;dunkelgraue Mergelschiefer als anstehendes Gestein an der Boca dos
Playosquot; (p. 60), according to Martin (30) possibly belonging to a Cretaceous
formation comparable with that of Cura9ao and Bonaire, are common tuff-rocks
in the schist-tuff series (see also J. H. Kloos (25) p. 48).

Martin (30), taking into consideration the distribution of the schist-tuff-
rocks to the best of his knowledge, came to the conclusion, (p. 56) quot;dass die
Sedimentargesteine das Liegende der Diabase darstellenquot; and are older than the
diabases. The occurrence and distribution could be very well understood, accord-

und om,t m dem höchsten Theile des Gebirges, woselbst die Erosion am wirk-
samsten that,g war, blossgelegt werden mussten.quot; Kloos (25), however who

rocfe. In many places the rocks occur as a pell-mell. Especially in the southern

parts of the formation, however, the diabase occurs as large Lsses and tatTr-
calahons in the schists. If we look at the map and take into consideration he
prevailing E-W strike of the schist-tuff-rocks we see several diabase beds^d
masses bordering more or less conformably „n the schists and tuffs. There quot;e
however, also many diabases which lie unconformably between the other rocks
rr« quot;quot;«^es and beds in the southern parts strike N 80 E, N 70 E, N 60 E
and K 50 E, hence differ rather much in strike with the surrounding schists

the diabases - which obviously belong to the series of diabase-tuffs - must have

dikes .quot; these beds. Although locaUy the diabase is maeroscopically a little

schisty (f.i. N 75 E) folding cannot be recognized in these rocks which bIhL d
rigid masses between the bedded tuffs.

Where the diabase lies unconformably in the other rocks, the unconformity
locally might also be the result of faulting during the folding.

The older formation consists, besides of diabase, schists and tuffs also of
conglomerates and breccias. Many of them contain pebbles of diabase and can

They do not contain diabase fragments. There is a great difference between them and
so they will be described apart from each other. Some have a more or less conglomeratic
character; others have an indistinct, breccious character. The green to gray to purple fragments
are irregularly shaped, acute-angular or rounded-off, and lie in a grayish to green to yellowish
cement. Fragments and cement may be not sharply bordered.

The cement of A 727—D 12691 (W of Dos Playa) is a pressed plagioclase aggregate,
with some chlorite, pyrite, magnetite and calcite. - Fragments and minerals: 1. fragments
of a very finegrained hornblende aggregate with grainy, pressed quartz, some ore and albite,
in reticulated texture; this plagioclase and that of the cement seem to be the same. 2. very
fine-structured hornblende aggregate, here and there calcite-bearing. 3. some pyroxenes and
plagioclases. 4. strange, grainy aggregates, the elements of which are browny in the centre
and biaxial-positive. 5. irregularly shaped isotropic masses. 6. PPdiabase.

The cement of A 732—D 12696 (SE of Dos Playa) is a dusty, grainy aggregate of partly
lamelled albites with here and there some quartz, the whole somewhat parallel-structured.
Many epidote grains and prisms and Pprehnite crystals are present; besides, some pyroxenes
and apatites. - The fragments, more or less surrounded by an aggregate of Psericite, Pprehnite
and epidote, are 1. very fine-structured hornblende felt, with or without epidote. 2. epidote
masses and 3. chloritic and isotropic masses. Little ore is present.

The cement of A 736—D 12700 (Rooi Dwars, near Boca Prins) is a dirty-looking Psiliceous
aggregate with quartzes, pyroxenes, pyrite, magnetite and Pprehnite-nests. The fragments
are 1. chlorite with a rim of Pprehnite. 2. chlorite masses with small quot;sunsquot; and crystals
of Pprehnite, and some quartzes and plagioclases; many of these masses have a Pprehnite
rim too. 3. aggregates of Pprehnite. 4. aggregates of Pepidote with quartz, chlorite and
Pprehnite amygdules; transitional into (2.). 5. some hornblende felts with plagioclases and
pjo-oxenes.

The cement of A 730—D 12694 (near Boca Prins) is a pressed-looking quartz aggregate
with epidote and some limonitic magnetite. The quot;fragmentsquot; look like concretions; their
periphery is brownish. They are yellowish-transparent in section; some are quite isotropic,
others for the greater part. They are extremely finegrained aggregates; each quot;grainquot; is
radial-fibrous. Curious and very small, oval elements lie scattered in the quot;fragmentsquot;.

The cement of P 77—D 6543 (top Jamanota) is grainy epidote with quartz and some
magnetite. The fragments are 1. diverse- and parallel-fibrous hornblende aggregate, with or
without epidote; a single fragment with remnants of PRadiolaria. 2. a few grainy epidote
aggregates. 3. looks like a chert and is transitional into (1). 4. a diverse-fibrous aggregate
of hornblendes, some quartz and epidote. 5. some hornblende crystals.

The cement of A 731—D 12695 (NW of Boca Prins) con,«ists of chlorite with zoisite.
grains and prisms and some limonitic magnetite; in several places Pprehnite needles andquot;
prisms, surrounded by quartz grains, occur, the whole with a dark rim. The fragments are
very fine-structured, diverse-fibrous hornblende aggregates, here and there with plagioclase
laths.

Since the most typical pebbles and fragments in these rocks are diabase, whethei
uralitized or not, we can call them diabase-conglomerates. Some of the rocks have a more
breccious character.

Since many rocks contain the same types of diabase it is better first to give a general
description of these types. - 1. The diabases, whether uralitized or not, are normally ophitic.
- 2. The diabases can be quite compared with the quot;Dichte diabaas met plagioklaasnaalden,
■die tot onvolkomen bundels divergeerenquot; (G. J. H. Molengraaff (31) p. 31). They are
aphanitic, dark rocks. The long plagioclase laths diverge in imperfect bundles and are often
bent. Allotriomorphic augite grains lie between these plagioclases. Chlorite may be present,
as an alteration mineral or in amygdules. The uralite-diabases of this kind show the same

individuals between the plagioclases and has, by that, a plumy development. It replaced

Zerrr^rrr T P^-gi-l-es, so that in some rocks the uralite takes up much
Tth Znbsp;^nbsp;(type a, uralitized or not). - 3. The diabases can be compared

augiet-mikrohthbundelsquot; (G. J. H. Molengraaff (31) pp. 31-32). The rock is aphanitic

af. 'T, T,quot;quot;nbsp;^quot;gite phenocrysts. The plagioclase occurs as laths and

as needles The augite occurs as grains and as spherolites. When uralitized, the uralite is
present as fibrous grains and as spherolites; uralite phenocrysts. (type fc, uralitized or not). ^
4. The diabases can be quite compared with the quot;Dichte diabaas met augiet in flink ontwik-
kelde schoofvormip mikrohthbundelsquot; (G. J. H. Molenghaaff (31) p. 32). They are aphani-
üc and microporphyritic. Only a very few phenocrysts occur and are plagioclase and pyro-
xene. The plagioclases are only few in number and occur as laths and needles. The pyroxene
occurs almost wholly as very fine-structured spherohtes; in some rocks these spherolites are
browncoloured. Ore is very fine-scattered in these spherolites. The rocks are finer structured
than type a and differ only slightly from type b. When uralitized, the uralite occurs in
spherohtes too; pyroxene and uralite can be distinguished only with difficulty in these rocks
Urahte phenocrysts. In some rocks, chlorite or epidote occur between the spherolites rarely
m their core (type c, uralitized or not).nbsp;'

Some fragments are not sharply bordered on the cement. The pebbles vary in size
They reach a maximum size of about 5 cm. but many of them can be seen only under the

12701 The cement is a microbreccia of partly sericitized plagioclases, colour-
less augites, magnetites (diabase-constituents!), between which epidote, chlorite and locally
also quartz occur. The rock-fragments are: 1. normally ophitic diabase. 2. type 3. type c
4. a strongly magnetitized and limonitized, very fine-structured, diverse hornblende aggregate

with locally some plagioclase, some pyroxenes and more epidote grains. 5. some smalf chert-
like fragments.

The quot;cement;' of A 738-DD 12702, 12703 occurs as strings between the fragments
and IS an isotropic, epidote-rich mass. The rock-fragments and enclosed minerals are 1
type c. 2. fragments, consisting of a very finestructured, partly isotropic siliceous and plagio-
clase aggregate with much epidote, sericite, chlorite, rare magnetite and pyrite, and here
and there enclosed plagioclases and remnants of PRadiolaria. Veins of quartz with epidote
ch onte and muscovite. Altered tuff). 3. some fragments, consisting of quartz, chlorite and
epidote. 4. some plagioclase crystals; a single one is broken and cemented by chlorite

Martin 107 and 116 have been described by Kloos (25. p. 48). Although Martin called

them diabase-conglomerates, Kloos did not recognize them as conglomerates but described

them as diabases with an quot;abrupte Wechsel in der Structur, der erst durch das Mikroskop

enthüllt wird. In fact, 116 is not conglomeratic in the sections and is a loose pebble -

Martin 107 has a microbreccious cement of plagioclase fragments and augite grains in a

plagioclase or quartz aggregate. Its rock-fragments are 1. ophitic diabase. 2. type a. 3. type c

4. a pebble of a very fmegrained quartz-epidote-aggregate. Martin 116 only shows
type a.

The rocks 3230 I-D 2291, 3230 II-D 2292 and 3232-D 2293, sampled by professor
J. A. Grutterink contain the types a and c.

A 733—D 12697. The cement is a Psiliceous aggregate with locally calcite and with
plagioclase, pyroxene and some quartz crystals. The pebbles: 1. fine-ophitic dikbase with
a tendency towards type a. 2. type c. 3. most of the fragments are extremely finegrained and
cannot be recognized (Pdiabase). 4. some browny isotropic elements

A 726—D 12690. The cement is a quartz aggregate with some chlorite and calcite.
and contains the fragments: 1. fine-ophitic diabase. 2. an quot;ophiticquot; rock of little sericitized
plagioclase (andesine, labrador) and quartz, with some chlorite, calcite, pyrite and leucoxene;
locally also allotriomorphic potashfeldspar (this rockfragment may be of a foreign origin,
and seems to be the groundmass of a porphyritic rock). 3. a diverse-fibrous aggregate of horn-
blende needles, with grainy plagioclase, little quartz and pyrite. 4. a fine-structured horn-
blende felt. 5. a coarser hornblende felt with quartz grains and nests, chlorite individuals with
blue interference-colours, and some pyrite.

A 728—D 12692 (between Dos Playa and the uppercourse of Rooi Fluit). The cement
is a pressed-looking, grainy aggregate of mainly plagioclase (partly lamelled oligoclase-
andesine) and less quartz. Here and there accumulations, bundles and quot;starsquot; of diminutive
hornblende needles occur, and locally some calcite and chlorite too. Pyrite and magnetite. The
fragments and minerals are 1. type a, uralitized. 2. extremely fine-structured hornblende
aggregates with a few plagioclases; they show here and there a reticulated texture with
some chlorite. 3. some partly uralitized pyroxenes, uralite crystals and plagioclase prisms.

A 729—D 12693 (the long hill-ridge between Arikok and Dos Playa). The cement is an
epidote mass, at the same time a hornblende felt, in which occur many hornblende and
plagioclase fragments, a single quartz and also very small fragments of uralite-diabase and
hornblende felt. The bigger fragments are: 1. ophitic uralite-diabase. 2. type a, uralitized. 3.
type c, uralitized. 4. very finegrained epidote aggregate. 5. as 4 but full of parts of hornblende
felt; moreover, a few plagioclases and hornblendes may belong to the cement.

The cement of A 734—D 12698 is a pressed-looking quartz-plagioclase aggregate with
epidote and ore, which seems to have partly resorbed some of the rock-fragments and which
occurs as veins in the latter. The pebbles are: 1. type a, uralitized. 2. type c, uralitized. 3.
some plagioclases and hornblendes.

The cement of A 735—D 12699 is an epidote mass with nests of pressed-looking quartz
and rare magnetite. The fragments are: 1. ophitic uralite-diabase. 2. type a, uralitized;
the uralite almost totally replaced the plagioclase in some fragments. 3. some epidote aggre-
gates. 4. some loose hornblendes.

Martin 110 has been described by Kloos (25, p. 55) and has not been recognized by
him as a conglomerate either. The cement is siliceous and contains epidote, ore and many
uralite and plagioclase fragments. The rock-fragments are: 1. ophitic uralite-diabase. 2.
type a, uralitized. 3. type b, uralitized. 4. type c, uralitized.

The rocks 3303—D 2354, 3304—D 2355 and 3305—D 2356, sampled by professor J, A.
Grutterink, contain 1. normally ophitic uralite-diabase 2. type a, uralitized. 3. type b,
uralitized. The two latter rocks moreover type c. uralitized.

A 656—D 12656 (near Dos Playa). The grainy and greenish rock has a psammitic texture.
Its cement takes up a little more room than the grains, and is a very finegrained Psiliceous
one, in which many, probably authigenous, diminutive sericite plates and chlorite occur.
A little granular titanomagnetite with leucoxenic flocks is present. Allogenic constituents
are many small quartz crystal-fragments.

It is questionable whether these quartz fragments are terrigenous constituents (originat-
ed from older, pre-existing rocks) or whether they originated from the neighbouring volcanic
rocks; hence, whether they are foreign minerals or whether they must be considered as
tuff mineral from the diabasic magma. In connection with the occurrence of diabase-conglom-
erates and breccias on the island the foreign origin of the quartzes is probable.

seems to be relatively young and is probably connected with the diorite intrusion

The very fmegramed hornblende aggregates, which occur as fragments can
S can trT'quot;^''^'^ hornblende-schists (metamorphic tJfs) If'tS^
Zrnhinbsp;have been enclosed before the metamorphism

(hornblendization) or after the metamorphism. In the first case, the breccias should
have been formed together with the tuffs and out of these rocks. It is howev^
mcomprehenszble, that in this case the hornblendization of the enclosed tuff frag-
ments should have occurred in that part of the older formation of which the

also a third possibility, namely, that the hornblende-rocks are different from the

widespread in the older formation
but have not been found m the southwestern part (E and NE of Spaansch Lagoen).
They occur as concordant beds between the schistose and tuffoid rocks Lch

less steep (f.i^SO S). The thickness of the beds varies; in some places a thickness

ot 25 m. has been measured. In the outcrop SE of Fontein f.i. a N 110 E striking

rocks they form here and there tops. So f.i., they occur on the top of the Jamanota

mere the conglomerates lie near the diorite-contact they are strongly invaded
by vems, f.i. SW of Seroe Boonchi.nbsp;i^ivauea

There is a striking agreement between the distribution of the urahtized
diabase-conglomerates and that of the urahte-diabases. which means that the
considerations on the nature of the process of uralitization (see diabases) also hold
good with regard to these conglomerates. - The rocks occurring SE of Fontein
and near Dos Playa do neither show uralitization in the cement nor in the diaba e
pebbles. They contain, however, very finegrained hornblende aggregates which
may have been enclosed as such in the conglomerates. In that cfse thes^Iom
blende-rocks must have been present as such together with the unaltered diabases
and diabase-tuffs, and even may be still older. - The rocks occurring W of Do
Playa and on the top of the Jamanota show uralitization both in the Lment and
in the diabase pebbles. The urahtization in the cement can occur only as an altera-
lon of the pyroxene crystals and also as a hornblendization of the whole mass
ZT^ V Tnbsp;hornblende aggregate occur, but, since

;^th the dionte mtrusion (quartz, plagioclase, epidote etc.; resorption-phenomena)
The microbreccious cement gives the impression of being composed of tuff
material, which must very probably have originated from the close vicinity. The
clearly tuffoid fragments too originated from closeby, very probably

If we take into consideration the common occurrence of the diabase pebbles
types « and c in the conglomerates, the small distribution of these types in the
diabases of Aruba, and the true pebble shape of the cemented rocks, the conclusion
IS obvious that most of the diabase pebbles probably have not originated from
^e Aniba diabases Smce the rocktypes a and c are widespread on Curacao (see
Molengraaff (31)), we can admit that the probable origin of
these pebbles lies here, if not in the territory between
Curasao ^nd Aruba In this connection, it must be mentioned that a
M Tnbsp;U recht collection (C290-D 12212 Rooi Beroe, S of Seroe

Manuel - NW Cura9ao) is a conglomerate with diabase pebbles of type a (I)
The quartz grains found in several Aruba rocks of the older formation may have
originated from these regions as well.

Common properties of the minerals of the batholith: The bathohthic rocks, both
plutonic and dike rocks, show several common properties. Their plagioclases are, to a more
or less great extent, sericitized and epidotized. In many rocks there is a clear connection
between such an alteration and the occurrence of epidote veins. The latter mostly contain
quartz, and sometimes chlorite too. Several plagioclases have been albitized along fissures;
a strong albitization often is connected with a strong epidotization. In many rocks there can
be seen a connection between a strong alteration of the plagioclases and a strong distortion
in the rock. Distortion phenomena are wide-spread; they manifest themselves mainly in
the quartzes and plagioclases. The quartzes are slightly to strongly undulose, quot;Streifenquot;
quartzes, cataclastic or marginally cataclastic. The distorted plagioclases which occur less
often than the distorted quartzes can be undulose, bent, flexed, faulted or broken.

The plagioclases of most of the batholithic rocks show a polysynthetic twinning, rarely
a cross-lamelling. — Except in most of the lamprophyres the quartzes (the porphyrite and
vintlite phenocrysts too) contain fluid-inclusions which are arranged in planes (lines) as
though along former cracks. According to Iddings (23, p. 537) the secondary nature of the
inclusions is indicated in this case, a crack having been filled up with quartz except in the
spaces occupied by liquid and gas. The distribution may be indefinite too; Iddings calls the
latter primary fluid-inclusions. The quartz may contain limonite.

The hornblendes often show a fine twinning according to (100); the composition-plane
sometimes is irregular, and intergrowth may occur as well. Alteration is not common and
mostly a slight one. The alterationproducts are chlorite, epidote and rarely calcite. Undulose
or bent hornblendes rarely occur. — Many biotites have partly or wholly been changed into
chlorite with titanite; the titanite occurs as parallel and lenticular aggregates between the
cleavage laminae of the chloritized mica. Other alterationproducts are epidote and quartz;
the latter may be undulose. Some biotites are bent, fibrous or frayed, locally connected with
the chloritization. The secondary chlorite is fibrous or spherolitic and green-pleochroitic, with
beautiful, steely-blue or purple-blue interference-colours (-f character of zone); or it is
spherolitic, palegreen-pleochroitic with a greenish-grayish-brown, velvet-like interference-
colour (— character of zone). The chloritization begins along the cleavage-planes.

The above-mentioned properties of the minerals of the batholithic rocks have not been
mentioned again in the following rock-descriptions, except where necessary. It can also be
remarked here that some of the plagioclases of the contemporaneous dike-rocks and of the
aplites and the albitites are simply zonal and rarely show recurrence.

The bathohth is a quartz-diorite bathoHth. The quartz-diorites occur mainly
as quartz-hornblende-biotite-diorites, less as quartz-hornblende-diorites; quartz-
biotite-diorites are of a minor importance.

Macroscopic description: Depending on the amount of ferromagnesian minerals the
diorite is light- or darkcoloured. The rock is in general mediumgrained, rarely coarsegrained
and finegrained. The feldspar is grayish-white; the hornblende occurs as blackgreen or
black, well-shaped prisms (maximum length about 25 mm.); the quartz grains are gray,
here and there brown-yellow; the biotites are black, lustrous plates.

Samples: A 37—D 11949; A38-D 11950; A 43-D 11955; A44—D 11956- A 80
D 12048; A 81-D 12049; A 771-D 13069; A 775-D 13073. ' ^^ ' ^

The texture is holocrystalline and hypidiomorphic-granulose; the main constituent
mmerals are plagioclase, hornblende, quartz, (orthoclase) and (pyroxene)

Plagioclase is in general the most important mineral. It shows an isometric or more
pnsmatic development, and is idiomorphic or hypidiomorphic. Chlorite and calcite occur but
here and there in the plagioclase. The plagioclases are on the whole zonal; the peripheric zones
are more acid than the core, at least in those plagioclases where no reversal of normal order
of zoning (recurrence) occurs. It is commonly observed that the inner zones and cores of the
zonally built plagioclases are more nearly equant than the outer zones or the final shape of
the crystals (see also Iddings (21) p. 216). The cores of the zonal plagioclases are on the whole
niore altered than the more acid peripheric zones, and even the more basic recurrent zones
show a greater alteration than the acid ones. The plagioclases vary in composition from
^igoclase to andesine, and are especially oligoclase and oligoclase-andesine. In D 11955 and
D 12049 some plagioclases occur with quartz-bubbles or vermicular quartz; probably as a
result of resorption-action of the end-stage quartz-liquid.

Orthoclase, occurring only in a few rocks, is at any rate of minor importance, allotriomor-
phic, and younger than the plagioclase. In D 11949 the orthoclase works in with the plagio-
clase, and seems to be somewhat cataclastic.

Hori^lende is quantitatively most important in some rocks but is commonly the second
mineral. The crystals are here and there irregularly distributed in the rock and occur in
groups, as if they had drifted together. They are idiomorphic or hypidiomorphic. Many
hornblendes and plagioclases border on each other in an irregular way. Other hornblendes
are Idiomorphic with regard to the plagioclase, or enclose idiomorphic plagioclases. Cleavage
is always well-developed, and colour, pleochroism and extinction point to the common green
hornblende in most cases. Here and there the colour is more browngreen. In D 11950 and
D 12048 zonal hornblende has been found with a darker coloured, browngreen irregularly
shaped core, which possesses a h=gher refraction than the lighter coloured periphery Certain
sections through these crystals show spots of the lightcoloured periphery in the core because
of the irregular shape of the latter. Nevertheless, the extinction is for both parts one and the
same and that of green hornblende. It is questionable whether lightgreen biotite fibres and
spherohtic biotite, which locally have been found in hornblende, are secondary products or
of a primary origin. The hornblende looks here and there bleached. In some hornblendes very
small quartz-bubbles or very small vermiform quartz-inclusions occur in great or small quan-
tities. These inclusions can only be recognized as quartz in very thin sections and also in
those places where they occur in connection with the normal quartz (fig. 8) About their '
genesis, see p. 95.

Pyroxene occurs only in D 11956 as a few colourless diopsidic augites, in intergrowth
with and surrounded by hornblende. It contains some limonite and ore, and has been partly
or totally uralitized.nbsp;^

Quartz is interstitial between the older minerals, in greater or smaller amount. The
older mmerals plagioclase and hornblende often show resorption-holes. the latter having
been filled up with quartz (fig. 9). Around such resorption-holes some plagioclases possess a
kind of corrosion rim existing of diminutive, grainy, dusty particles. Similar rims occasionally
occur in the more acid zones of a zonal plagioclase with reversal of normal order of zoning
They are probably due to resorption and corrosion by a more basic liquid. About the signifi-
cance of this resorption-phenomenon, see p. 94.

^ ^ Accessory minerals: Apatite is common as small prisms and needles, enclosed in the
feldspar quartz and hornblende; occasionally it occurs in groups of grains.-Magnetite is
often tied to the ferromagnesian minerals. It sometimes occurs with a narrow rim of epidote
J^ocally the ore has been altered into limonite. or into leucoxene (titanomagnetite) — Titanite
IS occasionally present as more or less idiomorphic crystals, often near the hornblende and

the magnetite. Limonite has been infiltrated in some rocks, especially along the cracks of
the quartz, and between the crystals.

Samples: P 68—D 6168; A36—D 11948; A 41—D 11953; A45—D 11957- A 46—
D 11958; A 47—D 11959; A 48—D 11960; A 49—D 11961; A 50—D 11962; A 51—D 11963-
A 52—D 11964; A 53—D 11965; A 54—D 11966; A 55—D 11967; A 57—D 11969- A 58—
D 11970; A59—D11971; A60—D 11972; A61—D 11973; A 288—D 12299- A 291—
D 12300; A 304—D 12313; A 759—D 13065; A 761—D 13067; A 773—D 13071.

The main constituent minerals are plagioclase. hornblende, biotite, quartz, (orthoclase).

The feldspars have the same general properties as those of the quartz-hornblende-diorites.
— The average composition of the plagioclases seems to be a little more basic than that of
the plagioclases of the quartz-hornblende-diorites, andesines occurring in about the same
quantity as oligoclases and oligoclase-andesines. In a few rocks the cores are labrador; in D
12300 the core is andesine, the periphery oligoclase-andesine; in D 11971, D 11953 and D 13067
plagioclases occur with an andesine core and with an oligoclase periphery. In D 11971 some
microperthitic potashfeldspar occurs. —In many rocks we can see plagioclases, composed
of many zones, while such zonal crystals have a repeated recurrence; with this recurrence,
resorption effects are often connected, more basic liquid having partly resorbed an earlier
formed, more acid zone. In D 11970 f.i. such recurrence and resorption effects occur in a
big plagioclase composed of about thirty zones. In many rocks the following curious phenom-
enon can be seen: plagioclases composed of a core and one more acid zone show the mineral
of the zone, besides in resorption-holes of the core, also inside the core, as irregular spots.
It can be understood that such an occurrence depends on certain sections through plagio-
clases which show a partly resorbed core and a surrounding more acid shell. Especially in
D 11963 the described phenomenon is very clear (fig. 10); the more altered core is about
labrador, the fresh shell is andesine or oligoclase-andesine; the same twinning occurs in both.
The shell is in general not idiomorphic with regard to the quartz. — In D 6168 the acid shell
itself has a zonal character; its zones merge gradually and still more acid layers are present
around the resorptive layer. — In the rocks D 11972 and D 13067 myrmekitic plagioclase
borders on orthoclase. In D 11953 irregular, granophyric intergrowth of plagioclase and
quartz occurs. A plagioclase in D 11957 contains a zeolitic mineral (spherolitic, brown-yellow,
parallel extinction, -f optical character of zone, n gt; n-plagioclase). possibly pectolite or
okenite. — InD 12313 and D 13067 some plagioclases and hornblendes show resorption-holes
filled up with orthoclase.

The hornblende has the same general properties as in the quartz-hornblende-diorites.—
In D 11948 and D 12300 fibrous-looking hornblende occurs. The latter rock contains a horn-
blende with a very palegreen core, around which an ore rim; the core consists of many fibres,
passing off in the surrounding and normal hornblende. In D 11960 remnants of partly
resorbed homblende occur in a plagioclase; it is remarkable that a narrow rim of plagioclase

around the hornblende remnants is more acid than the rest of the plagioclase, and therefore
shows another extinction-angle.

Biotite is quantitatively the second dark mineral in most of the rocks; by exception
it may be more important than the hornblende. In many cases the biotites are found near
the hornblendes; or they occur in the rock as streaky aggregates, as if they had drifted
together. The plates are rarely idiomorphic, more hypidiomorphic or allotriomorphic. In
many rocks fresh biotite is no more present, only the wholly changed mineral. Primary
inclusions are apatites, magnetites and zircons. Pleochroic haloes have not been observed.
Sagenite-textures are rare. As to the genetic relation between biotite and plagioclase-
hornblende the following may be remarked. Where the biotites occur in quot;streaksquot; between the
other minerals the former probably crystallized in an early stage of the magma consolidation.
Generally, the minerals border on each other in an irregular way. In some cases, idiomorphic
plagioclases and hornblendes lie inside the allotriomorphic (chloritized) biotite. Quartz
probably is always younger than the biotite. It is questionable whether resorption-holes are
present in the biotite. Here and there it borders on the quartz with a black ore rim; the latter
may be a corrosion-rim.

Quartz is in general the same as that of the quartz-hornblende-diorites. In D 11972
big quartz individuals poikilitically enclose many idiomorphic and hypidiomorphic plagio-
clases and hornblendes. In D 12313 and D 13067 the quartzes locally lie in crystal-groups.

In several rocks the apatite occurs included in magnetite. Magnetite is the same as in
the quartz-hornblende-diorites. Titanite is occasionally present, and near the dark minerals;
it may occur around magnetite, perhaps as a secondary mineral (titanomagnetite). Apatite,
magnetite and titanite occur here and there in groups, f.i. in D 12313. — D 11963 contains
pyrite with a magnetite rim, around which an epidote rim is found. — D 11959 seems to
contain some hematite tied to epidote, especially in feldspar. — Curious complexes of many
magnetite grains in chlorite (D 11973), and groups of magnetites, apatites, chlorite, epidote
and titanite (D 11961) may have originated from biotite. very rich in magnetite and apatite
inclusions. — The genesis of chlorite-veins (D 11964), of calcite between quartz crystals
(D 11959) is connected with late-magmatic or postmagmatic processes.

In most of the diorites more plagioclase than hornblende is present; the few cases that
hornblende is the most important we have almost exclusively to deal with quartz-hornblende-
diorites. The quartz-hornblende-biotite-diorites with a small quartz amount possess but
little biotite; those with much biotite (as much as hornblende or more) are very rich in quartz,
the latter being the second mineral.

Samples: A 62—D 11974, just E of Hooiberg; A 72—D 12039, Seroe Canashito; A 73—
D 12041, W of Hooiberg; A 76—D 12044. Seroe Janchi.

Only in D 12041 a little hornblende is present. In general, the rocks are similar to the
described diorites, — The plagioclases of D 11974 are oligoclase. Its biotites are hypidiomor-

phtc. Chlorite in the plagioclase probably originated from biotite. D 12039 has very dusty
albites, and totally changed biotites. The rock A 76-D 12044 possibly occurs as a dike
Its texture is more hypidiomorphic-granulose than allotriomorphic-granulose. The plagio-
clases are oligoclases. Biotite is quantitatively the third mineral. Muscovite is present as a
few plates. In A 73-D 12041 the biotite crystals occur irregularly distributed. One part
of the rock IS coarser grained and contains less quartz, less magnetite, more biotite and a
few non-idiomorphic hornblende crystals; the other part is finer grained and contains more
quartz, more magnetite, in general less biotite, and no hornblende. For the rest there is no
fundamental difference between these two parts which merge. The plagioclases are oligoclase-
andesine. The hypidiomorphic biotites show here and there a sagenite-texture; their borders
look limonitic-leucoxenic.

Beside the described diorites some other types occur on the island, although locally
pbbroic quartz-hornblende-diorites. Seroe Colorado diorites, aberrant quartz-hornblende
(-biotite)-diorites and strongly altered diorites.

Gabbroic Quartz-hornblende-diorites (Samples: A 423—D 12508, upper-course of
Rooi Santoe; A 448—D 12524, W of Sumpina, near Matividiri): These rocks are on the whole
^milar to the normal quartz-hornblende-diorites, but there are some typical differences
The plagioclases, which are andesines, contain numberless diminutive, microlitic inclusions
like those of the pyroxene-gabbros and - gabbrodiorites (see there). The hornblendes have
an irregular shape and partly enclose idiomorphic and hypidiomorphic plagioclases. They
have been clearly resorbed at their borders by a quartz-rich residuum and contain many
quartz-bubbles. There is a close connection between these resorption-holes and the quartz-
bubbles. Beside the bigger hornblendes, several aggregates of small crystals are present in
D 12524. Also much quartz and many quartz-bubbles occur between and in the crystals of
these aggregates.

The quartz-diorites of the serge Colorado: These diorites occur in a small outcrop
on the SE-cape of the island (see the map quot;Dquot;). They are a little aberrant from the normal
quartz-diorites. Three samples have been examined: Martin 97, Martin 104 and A 39—
D 11951. The two latter rocks are about the same; Martin 97 forms a transitional type
between them and the normal diorites.

Martin 97 is, in general, normal. Here and there quartz and plagioclase intensively
work in with each other, so that the plagioclase-border contains quartz-drops: transition
into a plagioclase sieve texture. The hornblende is on the whole non-idiomorphic, and locally
has conformed to earlier crystallized plagioclases; it looks frayed. The biotite exclusively
occurs in aggregates of very small greenish-brown plates, which are tied to the hornblende
or have clearly conformed to the plagioclase crystals. Grainy and stringy titanite is present
m these aggregates. Very probably these aggregates are primary (see the relation with the
plagioclase).

A39—D 11951, a quartz-hornblende-diorite, is a darkcoloured dioritic rock in which
long apatite needles can clearly be seen. A hypidiomorphic-granulose texture, however not
a clear one, can be recognized. - The plagioclases (oligoclase to oligoclase-andesine) work in
with each other, or occur in intergrowth. They are very dusty and indistinctly broadly
lamelled. The plagioclases look very strange in account of numerous inclusions, being for
the greater part quartz-bubbles (sieve texture; the quartz-bubbles have different orientation)
■for the other part very small hornblende prisms and fragments, and also a few biotite plates'
apatite needles and magnetite crystals. Resorption-holes occur in the plagioclases as well
and have been filled up with the younger quartz. - Hornblende is present for a small part
as remnants of big, idiomorphic crystals, and for the greater part as aggregates of small
hornblende crystals, the latter still showing more or less the shape of the original big crystals.

In some aggregates remnants of the origina ] hornblende have been preserved. The small
hornblendes of the aggregates are partly idiomorphic; pleochroitic from dark-bluishgreen to
brownyellow; non-twinned; quartz-bubbles occur included. Between the small hornblendes
of the aggregates quartz occurs. - Besides as inclusions in the plagioclase. quartz occurs inter-
stitially. especially in groups of crystals. It contains numerous fluid-inclusions. Magnetite
is abundant, as grains, crystals or as big skeleton-shaped individuals, the latter lying m
hornblendes and plagioclases. The ore can especially be found in the hornblende aggregates.
Apatite occurs as many very long needles and prisms stretching through different plagioclases,
hornblendes etc. They are occasionally broken according to the basal cleavage (fig. 11).

Martin 104 has been described by J. H. Kloos and is about the same as A 39—D 11951,
The principal difference is the following: the plagioclase is more or less idiomorphic with
regard to the quartz or not at all idiomorphic; in the latter case here and there granophyr-
like intergrowths occur. Some reddish-brown, strongly pleochroitic grains with a distinct

Very probably the acid, late-stage consolidation-liquid has played a part in the alteration
of these rocks. The common, primary, green hornblende prisms have been transformed into
aggregates of possibly Na-rich. bluish-green hornblende, quartz and magnetite, for the
greater part, probably. The sieve texture of the plagioclases has come into existence by this
late magmatic action as well and can be compared with the normal myrmekite and horn-
blende-myrmekite. Quartz-liquid must have partly resorbed the plagioclase and must have
been impregnated in it (see p. 94). May be, also the dusty character of the plagioclases and
the occurrence of very small hornblendes and biotites in these plagioclases are connected

On the other hand, there is a striking similarity between these rocks and several of the
dioritic rocks which occur in the contactzone of the older formation (see f.i. the altered diorite
A 546—D 12573. NW-Aruba, and other rocks described in the chapter on the contactrocks).
So possibly, the Seroe Colorado diorites lie near the contact with older rocks, and owe their
aberrant properties to endomorphic contactmetamorphism.

Aberrant pyroxene-bearing quartz-hornblende-diorite. (A 426—D 12511): This
finegrained and darkcoloured rock contains about as much plagioclase as hornblende, less
quartz and a little pyroxene. The plagioclases are especially lath-shaped. Many laths are
idiomorphic with regard to the hornblende (sub-ophitic texture), although their outline is
not quite straight everywhere. Many are zonal; their composition is oligoclase-andesine to
andesine. Idiomorphic hornblende prisms are rare; many of the crystals have conformed to
the plagioclases. In many crystals there occur irregularly shaped pyroxene cores, which are
a little limonitic; the hornblende does not look uralitic, so that probably pyroxene and horn-
blende occur in normal intergrowth.

Aberrant quartz-hornblende-biotite-diorite (A 425—D 12510): The plagioclases
of this darkgrayish, finegrained rock are especially lath-shaped. Some bigger, non-idiomor-
phic crystals, simply zonal, look phenocrystic. Hornblende occurs as long prisms, badly
idiomorphic or non-idiomorphic. here and there in crystal-groups.

These two rocks occurring near Bushiribana are aberrant in granularity, in the crystal-
development of plagioclase and hornblende, and partly in texture and mineral-content. This
aberrance is very probably connected with the close neighbourhood of the gabbros and
gabbro-diorites of Bushiribana.

Strongly altered diorites: 1. A 40—D 11952 is an epidotized quartzdiorite. with
distorted albites. Quartz locally occurs in irregularly granophyric intergrowth with plagio-
clase. Hornblende and biotite have been almost wholly changed into chlorite and epidote. -
2. The rock P 82—D 6547 is a strongly pressed quartzdiorite with totally changed ferro-
magnesian minerals, which now are present as long-shaped or irregularly shaped chlorite-
epidote-calcite masses. The plagioclases too havebeenstronglyalbitized. sericitized, epidotiz-

ed and calcitized. May be also secondary quartz can be found. - 3. A 75-D 12043 a quartz
hornblende-bjotxte-diorite. shows alteration-effects due to the neighbourhood of a yZge;
quartz-dxke Its plagioclases have been strongly altered. The hornblendes have been whoHy
transformed mto aggregates of chlorite, quartz and calcite. more or less with preservS
of the pnsm-shape and the biotites have been totally changed into chlorite witrtitan te
Ca c,te IS present between the crystals as well; chlorite, with or without calcite occursTn
narrow veins. - 4. A 750-D 13057 (Seroe Crystall) is a hornblende-epidote-rock. Hornblende

Only a little quartz is present between the other minerals or in quot;veinsquot;; it seems to have been
impregnated into the hornblende locally. Ore, apatite and titanite a e rare. nTs roS may

On the whole, the diorites occur in a weathered phase. Over large distances
the rock crops out as heaps of big, roundish and exfoliated monoliths (quot;Wollsack-
bildung , pillow-structure), which lie scattered in plains of diorite-detritus, and
which are autochthone. Where these heaps lie close together socalled quot;Felsen-

ifalso appears in very low elevations and
tliresholds (f.i. m the roads), or as common, little weathered, acute-angular rocks
Although the rocks are strongly weathered in many places the diorite can be
clearly recognized in those parts of the outcrop which have a greater hardness
and which have been preserved by selective erosion. So. it can be clearly seen that
the diorite occurs as lighter and darker coloured types which gradually merge into
each other, as well as in coarser and finer grained rocks. - Locally, the diorite

iN 135 E strike and a dip towards SW. The diorite in the outcrop N of Savaneta
seems to occur here and there in beds with an EW strike. The diorite can also
have a gneissose character; a strike of N 120 E in it could be measured.

As has been mentioned above the quartz-hornblende-diorite is less widespread
than the quartz-hornblende-biotite-diorite. The former does not form distinct
massives m the latter, but the rocks merge into.each other. This can be seen f i
m the sample A 378. The number of finding-places of the quartz-hornblende-diorite
seems to increase in the batholith outcrop from SW to NE (compare with the
gabbros, the porphyritic and lamprophyric dikerocks). The northern and northeast-

nfnbsp;a little chlorite, titamte and ore; see also 97. Abusively he cal% 144 a locS

ern parts in the outcrop are very probably the highest parts in the batholith.
- The quartz-biotite-diorites also merge into the quartz-hornblende-biotite-
diorites. They are of a very minor importance, and occur, as far as we can see,
only in the southern and southeastern parts of the batholith outcrop.

The diorite is not only batholithic but occurs, besides, as dikes in the older
batholithic massives, that is to say the gabbro and hooibergite massives, and as
dikes in the older diabase-tuff formation as well. The latter have been found as
normal wall-like dikes but also as pipe-dikes. It is very common that the diorite in
these dikes is porphyritic in the quot;Salbandquot;, here and there even vintlitic. Many of
the dikes lie in or near the contactzone between the older series and the batholith,
f.i. near Mira la Mar, near Seroe Boonchi, NNW of Arikok, E and NE of Santa
Lucia. A single dike crosses the contactzone. Some dikes, however, have been
found farther from the visible contact, that is to say, about 2 km W of Boca Prins
and in the diabase outcrop SE of Fontein. - The dikes contain here and there
fragments of metamorphic diabases taken up from the country-rock. A few
strikes of the dikes could be measured: N 40 E, N 75 E, N 100 E, N 110 E (two
dikes), N 135 E. The dike SE of Fontein has been strongly disturbed (orogenic
movements after the diorite intrusion).

DIORITIC ROCKS CONSOLIDATED BEFORE THE MAIN PART OF THE
DIORITES (SEGREGATIONS, ENDOGENOUS
INCLUSIONS)

These early crystallization products of the dioritic magma are darkcoloured, finegrained
rocks with several bigger crystals of plagioclase (max. about 8 mm.), hornblende (max about
8 mm.) and biotite (max. about 7 mm). These rocks are not sharply bordered on the normal
diorite, and their crystals normally work in with and between each other. They contain more
hornblende and less quartz than the diorite, but show in general the same properties as the
normal diorites. D 13065 and D 13067 contain a little potashfeldspar; it is curious that this
potashfeldspar is wanting in the normal diorite of D 13065. Some big plagioclase and horn-
blende prisms have no phenocrystic character. Some big biotite crystals in D 13066 and
D 13067, unaltered or partly altered, enclose poikilitically many non-idiomorphic plagioclases
and a few hornblendes, which stick partly in the biotite; and contain moreover ore, apatites -

These rocks occur especially in the northern and northeastern parts of the
batholith (compare with the gabbros) and form large endogenous massives on the
Seroe Plat, the Seroe Crystall and between these mountains and Seroe Gerard. The
diorite occurs in it as irregular dikes and streaks but also merges gradually into
these rocks. The rock has also been found as smaller inclusions in the diorite
between Ajo and Sumpina, near Koeroeboeri, N of Jaburibari, in the surround-
mgs of Alto Vista, on the Matoguera, NW of Hooiberg,

These dioritic rocks must have been segregated from the batholithic magma
and must have crystallized in the top of the batholith near the roof (see also the
gabbros). The finegrained character points to a quick cooHng. The dioritic magma
must have intruded into these roof massives and must have consoHdated at a time

when these massives were not yet quite consolidated (see the transition). The
smaller inclusions must have been loosened and some of them must have been
sunken in the batholithic chamber. It is questionable whether the original roof
phase was different from the rocks described here. The quartz and orthoclase
may be added minerals, in consequence of the flooding and reaction with younger
dioritic magma and with an end-stage consolidation residuum of this magma (see
f.i. N. L. Bowen (7) p. 199: quot;the magma can attack these inclusions, reacting
quot;with them in such a manner as to convert them into the crystals with which
quot;it is saturatedquot;). So the same residual liquid in the crystallizing dioritic mass
may have reacted with both the older minerals of the inclusions and those of
the diorite itself (see also p. 94).

In several places in the diorite landscape, which is in general a flat one, we
meet curious steep hills and smaller elevations, that have been preserved by
selective erosion. Fine examples of these hills and elevations are the high, cony
Hooiberg (164 m), E of Oranjestad, the Seroe Bientoe (85 m.), the Wara Wara(98m.)
the Seroe Compa, the Seroe Pretoe (E of the Hooiberg), the Turibanaand others.
These hills are composed of a beautiful, darkcoloured, igneous rock, in which
many big hornblende crystals are particularly striking. - It is a remarkable fact
that the above-mentioned massives of darkcoloured rocks present innumerable
dikes and veins of lightcoloured rocks in several places, especially at the borders.
Here and there these dikes are rather wide and contain smaller and bigger frag-
ments of the darkcoloured rock, which must have been loosened by and enclosed
into the intruding magma, that afterwards consolidated as lightcoloured dike-
rocks. The latter are proved to be mainly aplitic and dioritic rocks. Hence, the
darkcoloured rock must be older than the surrounding diorite, which sent its dikes
and veins into this rock (plate III, fig. 7—8).

Macroscopically the hooibergite-rocks are very beautiful and mostly coarsegrained
rocks, which are mainly composed of big and smaller, idiomorphic hornblende crystals (size
varying from about 1 mm to 15 mm.); these hornblendes lie in a fine grained, greenish,
brown-greenish or brown-grayish quot;groundmassquot;, which contains a certain amount of light-
coloured minerals. This quot;groundmassquot; takes up about as much room as or more room than
the bigger hornblende crystals.

Microscopic description: The hooibergites contain as main constituent minerals horn-
blende, plagioclase and quartz. In most of the rocks the hornblende is the most important
mineral and comes strongly to the front. In many of them this mineral takes up more room
than the plagioclase and quartz together. An exception is D 12314, with about as much horn-
blende as plagioclase. In by far the most of the rocks the plagioclase takes up more room than
the quartz, except in D 12318. Beside the differences in quantity of the main constituent
minerals with the common quartz-hornblende-diorite, there is another difference between

these hooibergites and the diorites. that is to say. the difference in the sequence of crystalh-
zation: only the hornblende crystals show idiomorphism, whereas both plagioclase and quartz
occur as allotriomorphic crystals interstitially between the hornblendes.

The hornblende is found in bigger, isometric crystals and in smaller ones, both short
prisms. The smaller crystals work in with the bigger ones (crystallization at about the same
time!), and lie, moreover, in and between the plagioclase and quartz individuals. In general,
the hornblende is idiomorphic with regard to the plagioclase and the quartz. The idiomor-
phism, however, is not everywhere absolute; this may be caused by a certain resorption-
action after the crystallization of the hornblende and before that of the plagioclase and
quartz, or it may have been caused by the fact, that plagioclase and quartz began their
crystallization at a time, when the crystallization of the hornblende was not quite finished.
The hornblende is the normal green one; in D 12314 some hornblendes possess lightgreen
rims; in D 12315 the hornblende is here and there almost colourless; in D 12318 some big
hornblendes possess lightgreen and darkgreen zones. Some of the smaller hornblendes show
twinning. Most of the hooibergites with intrusive dikes show diminutive quartz-bubbles
included in those hornblendes, which lie near or in the contact-zone (see also p. 96).

The plagioclase individuals occur as rather big and allotriomorphic crystals between
the big hornblende crystals and more or less poikilitically (as oikocrysts) around the small
ones. They are irregularly bordered on and work in with the quartzes (both of the same age!);
in D 12314 plagioclase and quartz occur in granophyric intergrowth, here and there. Thé
composition of the plagioclases ranges from oligoclase to albite; probably they have their
original composition. Some of the oligoclases in D 12314 and D 12318 seem to have a
slightly zonal extinction.

The quartz is granular and allotriomorphic between and around (poikilitically) the
hornblendes.

Accessory minerals: In most of the rocks a few apatite prisms and grains can be found
enclosed in quartz, plagioclase or hornblende. — In most of the rocks some titanite grains
occur, especially tied to the hornblende. — Magnetite occurs as a few small grains; a single
crystal has an epidote rim.

Hence, the probable sequence of crystallization is the following: Hornblende began to
crystallize; only in the second place the remaining part of the magma crystallized to a more
or less aplitic mass of plagioclase and quartz between the already existing hornblende
crystals.

Hooiberg: P 101-D6560; A 326-D 12318; A 327-D 12319. Seroe Bientoe: A 352-
D 12330. Seroe Pretoe (NW of Hooiberg): A 328—D 12320. Seroe Pretoe (E of Hooiberg)-
A 324—D 12315. Cashero (Seroe Compa): P 81—D 6546. S of Seroe Compa: A 323—D 12314
Seroe Tres Kabees: A 325—D 12317.

Macroscopic description-: The pyroxene-hooibergites show big and small, idiomorphic
hornblende crystals in a finegrained quot;groundmassquot;, greenish or greengrayish (in this quot;ground-
massquot; hornblende and feldspar can be distinguished). The quot;groundmassquot; takes up about as
much room as, or more room than the bigger hornblendes. The rock A 333 is very darkcoloured ■
the distinction between the big hornblendes and the quot;groundmassquot; here, is not so clear, so
that this rock looks more gabbroic. A 335 is a very darkcoloured hornblende-rock, -w^ith
plagioclase-quartz nests, regularly scattered.

Microscopic description: The main constituent minerals are hornblende, pyroxene,
plagioclase and quartz. Potashfeldspar has been found in D 12326, beside plagioclase'.
Hornblende is most important and takes up, on the whole, more room than the pyroxene.
Plagioclase generally takes up more room than quartz, or is present in about the same
amount. Hornblende together with pyroxene take up (much) more room than plagioclase

together with quartz. In D 6178 the homblende seems to take up more room than pyroxene,
plagioclase and quartz together. The rock D 12328 is somewhat different in parts from thé
others; it exists of groups of big hornblendes and pyroxenes, between which aplitic, allotrio-
morphic-granulose nests of plagioclase and quartz occur, also visible macroscopically. The
hornblende-pyroxene groups also contain some allotriomorphic plagioclase and quartz, and
on the other hand some hornblende crystals, mainly idiomorphic, can be seen in the plagio-
clase-quartz nests. — The main differences between these pyroxene-hooibergites and the
normal, dioritic or gabbroic plutonic rocks are the differences in quantity of the main constit-
uent minerals and the difference in the sequence of crystallization: only the hornblende
and the pyroxene show idiomorphism.

The hornblende can be compared with that of the hooibergites in dimensions, colour,
shape, idiomorphism and texture-relations with plagioclase and quartz. Some hornblendes
are brownish-green or have browngreen and lightgreen zones (D 12328). Many pyroxenes
stick in the hornblende crystals; hence, many of the hornblendes do not show a fine prism-
shape. In D 6561 and D 12324, which are very rich in pyroxene and in which the quot;ground-
massquot; takes up more room than the big hornblendes, the smaller hornblendes mainly occur
in a mass of pyroxene crystals, which are moreover intergrown with many of them. Som'e
secondary fibrous hornblende occurs in D 12322 and D 12326. A part of one of the big horn-
blendes in D6177 is of a very lightgreen and is composed of several irregularly shaped
individuals; lines of Pore radiate from this part into the surrounding normal hornblende.
It is very curious in D 12324, that plagioclases are irregularly intergrown with some big
hornblendes. The hornblendes, which lie near or in the contact-zone caused by the intrusive
dike-rocks, possess very small quartz-bubbles (see also p. 96)

The pyroxene occurs as prisms and crystalgrains between the big hornblendes, and in
and between the plagioclase and quartz individuals. They stick in the bigger hornblendes,
so that in the slides several hornblendes seem to enclose poikilitically many pyroxene crystals;
around several of these pyroxenes narrow rims of lighter green hornblende occur, which have
the same extinction as the whole crystal; in these spots the homblende is a little thinner,
on account of the underlying, colourless pyroxene in the slide. Pyroxene crystals rarely show
idiomorphism with regard to the hornblende; in general, pyroxene and hornblende are of
about the same age: both work in with each other, and most of the pyroxenes are intensily
intergrown with hornblende. As to the relation between pyroxenes and plagioclase-quartz,
the former generally are idiomorphic with regard to the latter. The pyroxenes are colourless
to very lightgreen diopsidic augites. In most of the rocks some twinned pyroxenes occur;
in a single intergrowth of pyroxene and hornblende the two minerals have the same twinning-
plane (see f.i. D 12326). Many pyroxenes are more or less Plimonitized along their
cleavage-planes and along fissures.

The plagioclase occurs as allotriomorphic individuals between and around the hornblen-
des and pyroxenes. The rocks D 12324 and D 6561, very rich in pyroxene, contain only a
very little plagioclase and quartz, allotriomorphically between the pyroxenes. The plagio-
clases are irregularly bordered on and work in with the quartzes ; only in D 6559 some plagio-
clases are more or less idiomorphic with regard to the quartz. A kind of granophyric inter-
growth between both minerals can be seen in D 12322. The composition ranges from oligo-
clase-andesine to albite, probably the original composition. D 2277 contains asingle zonal
crystal.

Potashfeldspar can be found only in D 12326, as a few allotriomorphic crystals of
Pmicrocline; it is particularly striking, that part of this potashfeldspar is also allotriomorphic
with regard to idiomorphic quartz!

Quartz, apatite, titanite and magnetite occur in the same way as in the hooibergites.
D 12321 contains a hornblende with a big, more or less skeleton-shaped titanite.

In connection with the characters of the different minerals, the probable sequence of
crystallization is the following: Hornblende and pyroxene began to crystallize; only in the
second place the remaining part of the magma crystallized into a more or less aplitic mass
of plagioclase and quartz, between the older hornblendes and pyroxenes.

Hooiberg: A 331—D 12323; A 332—D 12324; P 99—D 6177; P 99—D 6178quot; P 100—
D6559; P102—D6561; Martin 157—D 2277. Seroe Bientoe: A 336—D 12329- A 353—
D 12331. Cashero (Seroe Compa): P80—D6I7I. Seroe Pretoe (NW of Hooiberg)• A 328
-D 12320; A329-D 12321. N of Zumbo: A 330-D 12322. Turibana: A 333-D 12326
Jaburibari: A 335—D 12328.

Hooibergite and pyroxene-hooibergite (pyroxene-bearing hooibergite) merge into each
other in A 328-D 12320. This can be clearly seen in . the sample: the brownish-grayish
quot;groundmassquot; of the hooibergite merges into the greenish-grayish one of the pyroxene-
hooibergite. The transition in D 12320 is a continuous one, that is to say, the crystals of the
two rocks work in with and between each other in a regular way.

The rock A 334—D 12327 is more or less transitional between pyroxene-hooibergite and
quartz-hornblende-pyroxene-diorite; it is a dioritic pyroxene-hooibergite, from the top of
the Seroe di Poos di Noord. Generally it agrees with the normal pyroxene-hooibergites; the
main difference is, that the plagioclases are more or less idiomorphic with regard to quartz
and potashfeldspar and that they finished their crystallization at about the same time as
hornblende and pyroxene. Hornblende is most important; the pyroxene takes up less room
than feldspar. Hornblende and pyroxene are quite normal. The plagioclases are oligoclase-
andesines, some of which are zonal. Microcline occurs between and around the more or less
idiomorphic, darkcoloured minerals and plagioclase, and is irregularly bordered on the
quartz.

Another transition-rock is A 354—D 12332, a hooibergitic quartz-hornblende-diorite
which occurs at the southfoot of the Seroe Bientoe. The rock has the appearance of a common
diorite, with a hypidiomorphic-granulose texture. The plagioclases, however, are not idiomor-
phic with regard to the quartz; the hornblendes are idiomorphic or not with regard to plagio-
clase, and idiomorphic with regard to quartz. Hence, the texture agrees very much with that
of the hooibergites. The plagioclases are oligoclase-andesines. The hornblende occurs more
than plagioclase; some of the crystals have a darker core, and several hornblendes contain
numerous quartz-bubbles. Quartz is rather abundant. Narrow and small fissures through
some of the hornblendes have been filled with probably quartz.

The rock A 355—D 12333 is a transition-rock from the southeastern slope of the Hooi-
berg. It is a gabbro-diorite 'an andesine-hornblende-rock with gabbroic texture, and locally
a little quartz.

A 371—D 12340, occurring on the SE-foot of the Wara Wara, is a dioritic, finegrained
and darkcoloured transition-rock, an aberrant quartz-hornblende-diorite. A dioritic hypidio-
morphic-granulose rock, in which darkgreen, non-twinned hornblende is present'in many -
small and short prisms (not in bigger crystals). Many of the oligoclase-andesines are more
or less lath-shaped and zonal.

Hooibergites and pyroxene-hooibergites occur both in the same massives;
from f.i. the Hooiberg, the Seroe Bientoe, the Seroe Compa, the Seroe Pretoe
(NW of the Hooiberg) both hooibergite and pyroxene-hooibergite have been sam-
pled. Pyroxene-hooibergite seems to have a wider distribution than the hooi-
bergite, for the greater part of the samples proved to be pyroxene-hooibergite.
There seems to be no fundamental difference between both kinds of rock. As we shall
see below, the pyroxene-hooibergites are more or less metamorphosed into hooi-
bergitic rocks at their borders against intrusive dikes, that is to say, the amount

of hornblende in the contact-zone increases at the cost of pyroxene. So, all the
hooibergites might be metamorphosed pyroxene-hooibergites. In those places
where the pyroxene-hooibergites have come into contact with rather narrow dikes,
the metamorphosed zone has been developed only over a distance of some centi-
meters. Hence, if the hooibergites really are metamorphic pyroxene-hooibergites,
the metamorphism must have been caused by a much more active magma,
probably by the surrounding parts of the dioritic magma. Yet, the hooibergites
do not occur especially at the borders of the massives, no particular order existing
seemingly in their distribution. The Seroe Tres Kabees, however, seems to consist
only of hooibergites, not of pyroxene-hooibergites.

As to the nature of these hooibergite-rocks, they have quite the properties
of plutonic rocks. They are a little different from the diorites and are moreover
a little older, but still seem to belong to the rocks of the diorite bathohth.

Martin (p. 45 and 46) observed, that the darkcoloured rocks of the Hooiberg
show a more clear alternation with lightcoloured rocks at the borders of the
massive than in the centre. From these fieldobservations he drew the conclusion,
that the Hooiberg-rocks mainly represent concentrations of amphibole and augite
in the common quartz-diorite: (p. 46) quot;Ich schliesse aus diesen Verhältnissen,
quot;dass der Hooiberg den Mittelpunkt einer im Gebiete des Quarzdiorites statt-
quot;gehabten Zusammenziehung von Hornblende und Augit darstellt, welche sich
quot;im weiteren Umkreise des Berges allmählig verliert, bis das Gestein in den nor-
quot;malen Quarzdiorit übergeht.quot; Also Kloos (25) accepted this opinion: (p. 27)
quot;Die mikroskopische Untersuchung konnte diese Auffassung nur bestätigenquot; and
quot;so haben wir es augenscheinlich mit einem gleichalterigen Eruptivgestein zu
quot;thun, worin sich Augit und Hornblende lokal angereichert haben.quot;

Upon our renewed and nearer examination the hooibergite-rocks proved to
be of an other nature. The difference in age between diorite and hooibergite-rocks
could be clearly deterinined, although this difference seems to be only a small one,
and although the latter rocks very probably belong to the batholith-rocks, which
is proved by their mineralogical composition. As to the origin of the hooibergite-
rocks, we may consider them first-solidification-differentiates in the batholith
chamber. Very probably these differentiates came into existence against the
bathohth roof (see f.i. Daly (12) p. 245). It is questionable whether these rocks
have still this situation in the batholith, or not. In connection with the distri-
bution of the massives, the latter supposition seems to be the more probable
(see below)..At all events, the hooibergite-rocks crystalhzed before the diorites,
to irregularly shaped masses. Thus, the diorite magma could attack these already
consohdated masses and could intrude into them. Most of the intrusions have a true
dike-form, but here and there kinds of transition-rocks came into being (see p. 49).
Similar transition-rocks being darkcoloured diorites, rich in hornblende, surround
f.i. the massives of the Seroe Tres Kabees, of the Seroe di Poos di Noord, of the
Zumbo and others. So, in several places these massives do not border sharply on
the surrounding normal, dioritic rocks but merge more or less. Other massives,
however, f.i. the Hooiberg and Seroe Bientoe, are on the whole rather sharply
bordered on the surrounding diorite, which is a common lightcoloured diorite

here. For the understanding of the process of intrusion in the older hooibergite
massives, the remarks of Daly (12) on pp. 245 and 362 are very instructive

The principal finding-places are the following: Seroe Pretoe (NW of Hooiberg)
t!rnbsp;Ifquot;' ^t'Tnbsp;J-kuri and surrounding

Pretoe (E of Hooiberg), an elevation S of Seroe Compa, Seroe Compa, Zumbo
and surrounding tops, some elevations N of Zumbo, an outcrop on the south-
p11- mnbsp;^^^^^nbsp;S of Gabilan, outcrops on the Seroe di

part of the dionte-bathohth outcrop, whereas it is remarkable that they have
not been found in the two southeastern outcrops of the batholith. If the massives

the bathohth roof. It IS strange that they do not occur in the cloL neighbou?hood

of the boundary with the older diabase and metamorphic-tuff rocks, which in fact
constitute the bathohth roof. Therefore, we may accept that the hooibergite mass-
ives represent sunken fragments of this early crystallized, basic magma° whether
these fragments only sank over rather a short distance or quite down to tlquot;
bottom remains questionable. At all events, if the latter is true, the bathoHth
cannot reach very deep, and since it did not reach very high either, it may have
had a laccohth-shape (compare with H. Cloos (10) quot;Das Batholithenproblemquot;)
The shape of the hooibergite massives varies rather much. The Hooiberg and
Wara Wara are roundish in horizontal projection; the Seroe Bientoe has a very

of Kamai, and those S of Gabilan. - The strike of the oblong massives varies The

sen plate-shaped roof-masses, which have been sunken and tilted into an almost
vertical dostrinn

invaded by numerous dikes and veins, especially at the borders i). The dike rocks
are quartz-hornblende-diorites, quartz-biotite-hornblende-diorite, hornblende-
diorite, hornblende-granodiorite, dioritic aplites, biotite-granite-aplites, quartz-
rocks; rarely pegmatites and malchites.

Contacts of the hooibergites and pyroxene-hooibergites with intrusive dike-
rocks could only be studied at some dioritic aplites, quartz-hornblende-diorites
and hornblende-granodiorites. There seems to be no fundamental difference in
qualities between the contacts of these dike-rocks with hooibergite and those with
pyroxene-hooibergite. A difference between the contacts of the different dike-
rocks with hooibergite-rocks seems not to exist either.

Samples: Contacts between hooibergite-rocks and dioritic aplites: A 325—D 12317;
A 328—D 12320; A 332—D 12325; A 336—D 12329; P 102—D 6561. Contacts between
hooibergite-rocksandquartz-hornblende-diorites: A 324—D 12315; A 326—D 12318; A 327—
D 12319; P 81—D 6546; P 99—D 6178; P 102—D 6561. Contacts between hooibergite-
rocks and hornblende-granodiorites: A 352—D 12330; A 353—D 12331. Contact-phenomena
also can be seen in A 335—D 12328 (pyroxene-bearing hooibergite with aplitic nests).

Macroscopic contact-phenomena: Only those hooibergite-rocks, which are sharply
bordered on the intrusive rocks, possess a narrow rim, blackcoloured and very rich in horn-
blende, at the contact. This rim only could be found at the contact with some dioritic aplites
and quartz-hornblende-diorites: A 325 (about 3 mm. wide), A 326 (the rim occurs but here
and there), A 332 (less than 1 mm. to 5 mm. wide), P 81 (the rim is not very important),
P 102 (about 1 mm. to 3 mm. wide). On the other hand, the hooibergite-rocks, which are not
so sharply bordered on the intrusive rocks, do not show contact-rims. So, if the intrusion of
the dike-magmas took place at the time, when the hooibergite-rock was quite or about quite
consolidated (see the rocks with a sharp border), a contact-rim could develop. On the other
hand, if the intruision took place in a partly consolidated hooibergite-rock (see the rocks,
which are not sharply bordered on the dike-rocks), a contact-rim did not develop. Notwith-
standing the failing of a contact-rim in the latter hooibergites, these rocks still show contact-
phenomena, which can be detected under the microscope.

The dike-rocks in A 332 (dioritic aplite) and in A 352 and 353 (hornblende-granodiorites)
contain several fragments of hooibergite-rock, which have become inclosed in the liquid
dike-magma, during the intrusion of these dike-magmas; these fragments are only in A 332
very rich in hornblende (compare with the hornblende-contact-rim, also present in A 332).
A 353 contains, beside the hooibergite fragments, also inclosed hooibergite-hornblende
crystals; the latter are much bigger than the hornblende crystals of the granodiorite itself.

The different dikes are normally shaped; only the dike of A 336 is irregular. Narrow
tongues or apophyses originated from dioritic aplite dikes, can be seen in A 332 (quartz
tongues), A 336 (aplitic tongues), and P 102 (aplitic tongue, poor in hornblende). The dioritic
dikes in A 326 and P 99 show a flow-structure, manifested by the hornblende prisms, which
lie roughly parallel to the borders. The dike in P 81 contains hornblende crystals only in a
zone, 1 cm. wide, lying alongside the hooibergite, and not in the central part of the dike;
so, the peripheric part of the dike has the composition of diorite, whereas the central parts
look more aplitic and pegmatitic (quot;Nachschubquot; of the aplitic magma?). On the other hand,
the border of the dioritic dike of P 99 (some mm. wide) is free of hornblende; this aplitic border
sends an almost hornblende-free aplitic apophysis into the hooibergite-rock.

1) The massives must have been very much fractured at their borders, so that the
dioritic and aplitic magmas could easily intrude. The great quantity of aplitic intrusions
mav be connected with the (originally) high situation of the massives in the batholith,
if at least the massives came into being there. See also the considerations of Daly on
this strong invasion by acid magma (12), p.,245 and 362.

Microscopic contact-phenomena: Hooibergite-rock and the different intrusive rocks
can be clearly distinguished from each other, thanks to the difference in quantities of the
mam constituent minerals (especially of hornblende) and thanks to the difference in texture
Nevertheless, the rocks are not sharply bordered on each other (nor the hooibergites with
macroscopically sharp borders either!), and the crystals on both sides normally work in with
and between each other. - Notwithstanding the fact, that hooibergite-rock and intrusive
dike-rocks are not sharply bordered on each other, the intrusive dikes must be younger than
the hooibergites. Beside the fieldobservations, the pétrographie facts too point to this differ-
ence in age. So, the mtrusion of the dike magmas must have taken place at a time when the
hooibergite-rocks were not quite consolidated. As has been mentioned above, there must
have been local differences in the phase of consolidation during the intrusion (contact-rim
or no contact-rim). However, a certain magmatic solution of the older hooibergite-rock quite
consolidated, by the intruding magmas may have been one of the causes that after the
hnal consolidation, the crystals of both rocks have worked in with and between each other
Probably, also interchange of material has taken place to a more or less great extent

It is very curious, that the hooibergite in D 12318 contains more quartz than the quartz-
hornblende-diorite, which intruded into it.

Exomorphic contact-phenomena, magmatic stoping and assimilation in the
hooibergite-rocks: iVIagmatic stoping on a small scale can be seen in D 12325; the aplitic
magma worked here as a wedge and loosened fragments from the pyroxene-hooibergite-
one hornblende fragment quot;is on the pointquot; of tearing off from the pyroxene-hooibergite
(lig. 12). During the enclosing of hooibergite fragments by the dike magma,the latter intruded
mto these fragments here and there, so that the peripheric hornblende crystals have been
loosened and now lie like a garland of separate individuals around the fragments in the
diontic aplite. D 12330 and D 12331 too contain fragments of hooibergite-rock, enclosed in

D 12310, D 12325 and D 12331; the dike magmas or the final consolidation-residuum of
the dike magmas have assimilated parts of the hooibergite-hornblendes, so that now feldspar
and quartz crystals of the dike-rock stick irregularly in the partially resorWed hooibergite-
hornblendes.

Contact-phenomena in the hooibergite-rocks are manifested almost exclusively in the
hornblende minerals. It is a remarkable fact, that in the pyroxene-hooibergites, generally
the amount of hornblende in the contact-zone increases at the cost of pyroxene; even in
some rocks, the contactzone does no more contain pyroxene. It is also very remarkable,
that well-developed hornblende-contact-zones (without pyroxene) only occur in the pyroxene-
hooibergites (D 12325 and D6561). The pyroxene-hooibergites with a decreasing amount
of pyroxene towards the contact are D 12320, D 12329, D 6178 (compare with D 6177).

D 12320—A 328 consists of pyroxene-bearing hooibergite, hooibergite and a dike-of
diontic aphte, the pyroxene-bearing part of the hooibergite-rock being separated from the
aphte by the hooibergite. All three rocks merge gradually into each other; so, it seems to
be obvious that the pyroxene-hooibergite has been metamorphosed into a hooibergitic rock
at Its border by the intruding aplitic magma. Moreover, it must be mentioned, that the
composition of the plagioclase of the pyroxene-hooibergite is about oligoclase-andesine,
whereas the composition of the hooibergite-plagioclase is albite-oligoclase to oligoclase.

The hornblende-contact-zone in D6561 (pyroxene-hooibergite and dioritic aplite) is
about 4 mm. wide and merges gradually into the pyroxene mass of the pyroxene-
hooibergite; hornblende and pyroxene crystals on both sides work in with and
between each other. The distinction between this hornblende-contact-zone and the
diontic aphte is, of course, clear; however, the crystals on both sides also here work in
with and between each other in a quite normal way. The contact-zone is an aggregation of
grainy hornblende crystals, that include numerous small quartz-bubbles; some of the crystals
show a darker green core and a lighter green periphery. Between these hornblendes small
quartz nests occur, as it were interstitially; there is a connection between the quartz of
these nests and the quartz-bubbles in the hornblende. Also some non-idiomorphic plagioclases

altered and dusty crystals, can be found between the hornblendes. As accessory minerals
some very big apatite grains, and a very little ore are present; in the pyroxene-hooibergite
and very near this contact-zone the amount of magnetite increases. Probably, the pyroxene
of the border of the pyroxene-hooibergite has been transformed into hornblende plus quartz
(of thé contact-zone), as a result of the contact-action by the intruding aplite magma. The
hooibergite may also have been enriched with quartz out of the quartz-rich aplitic magma.

The contact-zones in D 12325 (pyroxene-hooibergite and dioritic aplite) are not so very
different from the hooibergite; the big hornblendes contain small quartz-bubbles; there is
less plagioclase than in the hooibergite, however more quartz between the pyroxenes; the
latter seem to have been partly resorbed by the quartz liquid, which may have originated
from the quartz-rich aplite magma. Magnetite is wanting. The enclosed fragments of the
pyroxene-hooibergite, lying in the aplite-rock, do no more contain pyroxene; they
consist of an aggregate of hornblendes (with quartz-bubbles), between which quartz and
plagioclase occur.

The hooibergite, bordering on the dioritic aplite in D 12317, is almost normal; among
the hornblende crystals, however, there are no big individuals; all are small, short prisms;
probably, this development of the hornblende is also the result of contactmetamorphism.

A contact-phenomenon, present in almost all the invaded hooibergite-rocks, is the
occurrence of small quartz-bubbles (in a more or less great quantity) in those hornblendes,
which lie near or in the contact-zone. The zone, in which such quartz-bearing hornblendes
occur, is different in width in the different rocks; for D 12318 a width of about 3 mm could
be determined. This zone in D 6178 contains a little more quartz than the proper pyroxene-
hooibergite farther from the contact; so, an enrichment with quartz out of the quartz
rich quartz-hornblende-diorite magma seems obvious. This enrichment has not only taken
place as an enlargement of the already existing, interstitial quartz masses, but also as an
impregnation of the hornblende crystals with quartz (quot;hornblende-myrmekitequot;; see also
p. 96).

It is curious, that D 12328, a pyroxene-bearing hooibergite without an intrusive dike-
rock but with aplitic nests (see pyroxene-hooibergites), contains some hornblendes with
quartz-bubbles. As in the diorites, the final consolidation-liquid, rich in quartz, must have
enriched the hornblende: autometamorphism.

Endomorphic contact-phenomena in the intrusive dike-rocks: Contact-phenomena
in the dike-rocks are rare. Only the following alterations in connection with the close neigh-
bourhood of the hooibergite-rock could be found. It is remarkable, that in most of the dike-
rocks the plagioclases are very or rather dusty. In D 12319, D 6178, D 6546, D 6561 the
plagioclases are especially very dusty close to the contact, and they are the more dusty, the
nearer they lie to the hooibergite-rock. - Some dioritic dike-magmas enclosed hooibergite-
hornblende crystals; at least, some big hornblendes in these dike-rocks look very much like
hooibergite-hornblendes: D 12315, D 12319, D 12331, D6178. The hooibergite-hornblendes
in the latter rock contain small quartz-bubbles! - D 12319 shows moreover the remarkable

phenomenon, that the zone of the quartz-hornblende-diorite-dike, bordering on the hooi-
bergite and about 4 mm. wide, is richer in quartz and hornblende than the diorite farther
away from the hooibergite, consisting for the greater part of plagioclase.

Matividiri, which borders on the diorite, on the sea and for a small part on the

hypersthene and augite-bearing gabbros and augite-bearing gabbros (gabbro-
diorites) .

The texture is typically hypidiomorphic-granulose-gabbroic. The main constituent
minerals are plagioclase, orthorhombic and monoclinic pyroxene, hornblende, biotite and
quartz. Quartz is wanting only in D 12528, biotite is wanting only in D 11945 Plagioclase
takes up more room than one of the other minerals. In general, the pyroxene takes up more
room than the hornblende, except in D 1194'3 and D 11945, which are rich in hornblende
The monoclinic pyroxenes take up more room than or about as much room as the orthorhomb-
ic ones. Biotite and quartz are generally of a minor importance, if present

The plagioclases are more or less prismatic. Except in the most peripheric parts they
look very dusty because of numberless diminutive microlites, occurring in very small
needles, rods and bent plates in several parallel-systems (these parallel-systems seem to be
connected here and there to lamel-systems); the distribution of the microlites has something
to do with the polysynthetic twinning and the zonal structure. The microlites look brownish ■
in reflected light and give the plagioclases a dark colour in the sample. Many of the
plagioclases have a zonal structure, here and there with (repeated) recurrence; the zonal
structure is more or less regular and has here and there quite the character of the curious
struci.ure m some of the plagioclases in D 11963 (see p. 40). The composition is andesine to
labrador; except in D 11945: bytownite to labrador-bytownite. In several rocks plagioclases
occy with green chlorite, uralite or biotite along fissures; these minerals are alteration-
products of the dark minerals. Only the rocks sampled on the Matividiri, Sumpina and Kadi-
wan contain several pressed crystals.

The monoclinic pyroxene crystals are hypidiomorphic, less allotriomorphic with regard
to the plagioclases. They are prismatic, very palegreen to almost colourless diopsidic augites
Several of them show a twinning. Some pyroxenes in D 11943, D 11945 D 12528 and D 12529
have quite changed into lightgreen, parallel-or diverse-fibrous uralite; in D 11943 and DI 1945
such urahte aggregates contain ore, partly as a rim.

The orthorhombic pyroxenes are idiomorphic or hypidiomorphic with regard to the
plagioclases, and in general idiomorphic with regard to the monoclinic pyroxene. Hence
the orthorhombic pyroxene must have crystallized before the augite. The crystals are short-
prismatic or isometric hypersthenes, with a slight pleochroism from very palegreen to very
pale-pink, and rarely colourless. The hypersthenes have been partly, along their border and
along fissures, or totally changed into talc, which occurs as a brownish, parallel-fibrous
aggregate; here and there some greeny uralite along the border of this talc aggregate and
a nm of ore are present as well.

The hornblende is, in general, non-idiomorphic; hypidiomorphic or allotriomorphic
with regard to the plagioclases. It is present in well-cleaved, light-or darkgreen-pleochroitic
crystals, which are of a primary origin. Hornblendes in D 11942, D 11943 and D 11945

contain small quartz-bubbles; several augites m D 11942 contain them too. In D 12528 the
transition hornblende -gt;■ uralite is clear.

Texture-relations hornblende -pyroxene (fig. 13); The augite crystals are intensively
intergrown with hornblende, that is to say, the latter mineral occurs as small pieces in the
pyroxene and in many cases also as an irregularly shaped rim around the pyroxene; these
different parts have one and the same extinction and belong to one and the same hornblende
crystal. Here and there the intergrown augite and hornblende have the same twinning-
plane (see f.i. D 11943). Also augites occur which are in intergrowth with two hornblende
crystals. The intergrowths prove that the two minerals must have crystallized at the same
time. (Probably it is out of question that the hornblende forms here a younger resorptive
replacement-mineral in and around the pyroxene, like quartz here and there in feldspar).
— No intergrowth can be seen between hornblende and hypersthene. The latter occurs as
rounded-off and hollowed-out crystals with a narrow hornblende rim or quite enclosed in
bigger hornblende individuals. The hypersthenes must have crystallized before the horn-
blende.

As to the relation between hypersthene and hornblende we must consider the genesis of
these two minerals by the light of the reaction principle as it has been described by Bowen
(7, pp. 54—62); see also Erdmannsdorffer (18, pp. 185 and 273). Hypersthene and hornblende
here occur very probably in a discontinuous reactionseries and have a reaction-relation.
During a phase of slow cooling the hypersthenes could react with the surrounding liquid and
have become rounded-off and partly hollowed-out. The following phase of rapid cooling
caused the crystallization of a hornblende quot;reactionrimquot; (in the meaning of Bowen) or
corona around the partly resorbed hypersthenes. So, in fact, the above-described relation
between the two minerals is due to the change in rapidity of cooling. — There are no such
reaction-relations between orthorhombic and monoclinic pyroxenes here, nor between the
monoclinic pyroxene and the hornblende either.

Biotite is present as a few and small plates, non-idiomorphic and especially in the close
neighbourhood of and around ore. In D 11942 it also occurs in intergrowth with hornblende.

Magnetite grains are especially tied to the dark minerals. Here and there they have
conformed to the latter and show an irregular shape. Very small ore particles occur besides
in alterationproducts also in some of the unaltered pyroxenes. — In most of the rocks a few
apatites occur. — Limonite occurs along fissures of some of the hypersthenes and augites.

Sumpina (S of Matividiri): A 452—D 12528; A 453—D 12529. Kadiwari (S of Matividiri):
A454—D 12530. Matividiri (near and N of the top): A451—D 12527. Wariroeri (near the
coast): A33—D 11945. Seroe Crystall: A 30— D 11942; A31—D 11943. W of Matividiri:
A 459. N of Zumbo: A 460. Near Seroe Janchi: A 458. i)

These rocks are darkcoloured, gabbroic or dioritic. The texture is hypidiomorphic-
granulose to gabbroic. There is more or less plagioclase than hornblende and pyroxene
together; at all events, the former is in general the most important mineral. The
hornblende generally takes up more room than the augite, while biotite is a third dark
mineral; the latter is wanting in D 11941, D 11947 and D 12526. Quartz is not very
important; its amount is greater in the dioritic and smaller in the gabbroic rocks.

1) Martin sampled two hypersthene-gabbros, one NW of Bushiribana (135) and another
E of Bushiribana (130*); the latter is free of quartz. Kloos considered all the homblende
secondary homblende after augite and hypersthene, and did not recognize the primary
hornblende. The uralitization of the augite and the alteration of the hypersthene into talc
in 135 have abusively been described by him as a beginning serpentinization of the horn-
blende. In 130* the augites have partly been uralitized and the hypersthenes show a begin-
ning alteration into both talc and uralite.

The plagioclases are about the same as those of the hypersthene-gabbros with regard to
the shape and the microlitic inclusions. It is very peculiar that plagioclases in D 11941 and
D 11968 are intergrown with quartz. Part of the plagioclases are simply zonal. The original
composition varies from oligoclase to labrador-bytownite. Distortion phenomena are com-
mon. Some crystals contain narrow veins of chlorite and of hornblende material, evidently
in connection with the alteration of the dark minerals.

Only in D 11947 and D 12525 some orthoclase occurs allotriomorphically between the
plagioclases and hornblendes.

The hornblende is the common green or browngreen one, rarely idiomorphic In most
cases it is as old as the plagioclase or it has conformed to and around the idiomorphic plagio-
clase crystals. According to the cleavage in the idiomorphic crystals the hornblende must be
primary. Quartz-bubbles may occur.

Monoclinic pyroxene is present as colourless diopsidic augites, which rarely occur as
separate and rather idiomorphic crystals and mainly are intergrown with hornblende. The
latter occurs as small pieces in the pyroxene and also as a kind of rim around it; here and
there a common twinning-plane exists. The intergrown pyroxene core may be limonitic along
the fissures. In many places the pyroxene has been uralitized, so that hornblendes occur
with a core of grainy or fibrous, secondary hornblende, here and there also with chlorite,
very finegrained ore a,ncl lt;^u3,rtz-bubbles. In 13 12521 no unaltered pyroxene is present*
several crystals consist of secondary hornblende, with chlorite and with a kind of chlorite
rim; the latter mineral probably originated from hornblende. Also in D 11954 and D 11968
the pyroxene has been totally changed into uralite, chlorite and leucoxene.

The quartz is interstitial. In reflected light the quartzes of D 12523 show a bluish colour,
caused by numberless filiform, microlitic inclusions.

The magnetite grains in some rocks have narrow rims of titanite, or are leucoxenized.
Apatite.

N of Santa Lucia: A 450—D 12526. Kadiwari: A 462. SE of Bushiribana: A 449—
D 12525. Bushiribana: A 42—D 11954; A 56—D 11968; A 445—D 12521; A 446—D 12522;
A 447—D 12523; A 461. Seroe Sumpina (N of the Crystallberg): A 29—D 11941. About 0,5
km N and NE of Seroe Janchi: A 444—D 12520; A 28—D 11940; A 35—D 11947. i)

During the course of the crystallization of these hypersthene-augite- and augite-gabbros
fractionation has occurred in consequence of the zoning of the plagioclases and of the forma-
tion of hornblende coronas around the hypersthenes. This fractionation has led to the
crystallization of plagioclase zones of an average to rather acid composition, of biotite,
quartz and in a single rock even of potashfeldspar. Compare with Bowen (7) chapter VI,
The fractional crystallization of basaltic magma.

A 34—D 11946 is a quartz-free hornblende-augitergabbro, sampled on the Jaburibari.
The gabbroic rock consists mainly of bytownite and hornblende; monoclinic pyroxene is
the second dark mineral. The pyroxenes are small, granular or prismatic, colourless diopsidic
augites, here and there twinned. Pyroxene and hornblende occur in intergrowth in the normal
way as well. A zeolitic mineral, possibly pseudomorphic after plagioclase, is colourless to
somewhat yellowish; parallel- to radial-fibrous or with forms of frost-flowers; low inter-
ference-colours; n lt; 1.53; parallel extinction; -(- zone. It may be natrolite.

A rock, which clearly shows the transition between quartz-hornblende-diorite and

1) Martin sampled two augite-gabbros, one on the Seroe Crystall (133) and the other
one in Bushiribana (133*). Kloos wrongly considered all the hornblende secondary after
pyroxene; part of it certainly is primary and is in intergrowth with augite. Some of the
augites in 133* seem to have been wholly or partly altered into ?talc.

hornblende-augite-diorite is A 32—D 11944, sampled about 1 km N of Alto Vista. Macroscop-
ically a darkcoloured, mediumgrained rock merges into a lightcoloured dioritic rock with
big hornblende crystals (up to 15 mm. long). - The quartz-diorite is rich in quartz and contains
zonal oligoclases; the latter take up more room than the hornblende. The hornblende contains
quartz-bubbles. Ore and titanite occur in intergrowth in a chlorite-titanite mass. - The augite-
diorite is more or less gabbroic. The plagioclases probably take up less room than the dark
minerals, of which hornblende is most important. They are irregularly zonal and show one
core and one zone; their composition could be measured as labrador to oligoclase. The
hornblendes show a pleochroism from browngreen to pale-brownyellow and are irregularly
coloured here and there, although their extinction is one and the same. The diopsidic augites
are intergrown with hornblende. Radial-fibrous chlorite with titanite, lying around ore. may
have originated from biotite. Quartz seems to be wanting. - The two rocks can be clearly
distinguished from each other because of the qualitative and quantitative differences in the
constituting minerals. There is no special transition-zone between them. On the other hand,
the rocks border directly on each other and their crystals normally work in with and between
each other.

The gabbroic rocks occur in the bathohth as darkcoloured massives which
seem to present only aberrant phases of the diorite and many of which have small
dimensions (see the finding-places and the map). They crop out as big and round
blocks (selective weathering) or as acute-angular rocks. Here and there the
massives lie on the top of the hills, f.i. of the Seroe Sumpina (N of the Seroe
Crystall), of the Seroe Crystall and of hills in N-Aruba. It is very remarkable that
the gabbro of the Matividiri locally shows beds, which have a strike N 90 E and
a steep dip to the south (the same strike as that of the porphyrite-dikes here!). The
massives occur especially in the northern and northeastern regions of the north-
western large bathohth outcrop. The most important finding-place is the large
gabbro-massive of Sumpina-Matividiri-Bushiribana, bordering partly on the sea.
As far as is known, gabbroic rocks are absent in the two southeastern diorite out-
crops.

The Matividiri s.str. seems to consist only of hypersthene-gabbro. The gab-
bros of Bushiribana and the surroundings are mainly augitergabbros without
hypersthene and for the smaller part hypersthene-gabbros. On the Kadiwari,
the Seroe Crystall and in the surroundings of Seroe Janchi both kinds of gabbro
have been sampled. So, these two gabbros'seem to belong to the same geological
unit; yet, true transitionrocks have not been found.

As to their geological place in the bathohth, Martin (30) considered the
gabbroic rocks rocks equivalent with and of the same age as the diorites: (p. 46)
„Gabbroartige Gesteine treten ebenfalls innerhalb des Dioritmassivs auf, ohne
„dass ihnen eine geognostische Selbständigkeit zugeschrieben werden dürfte.quot;
He mistook the rocks which represent the injected gabbros in the surround-
ings of Bushiribana for dioritic rocks with gabbroic concretions (compare with
his ideas concerning the hooibergite-rocks): (p. 47) „Von einer Formationsgrenze
„zwischen Gabbro und Quarzdiorit, deren Existenz schon auf Grund der beobach-
„teten, gabbroartigen Concretionen in Letzterem unwahrscheinlich ist, vermochte
„ich nirgends eine Spur zu entdecken.quot; Kloos (25) came to the same conclusion

on pétrographie bases and considered the gabbro an example „von einer lokalen
,,Aenderung des Gesteinscharakters inmitten eines eruptiven Massivsquot; (p. 38).

In fact, the diorites and the gabbros are, broadly outlined, not so very
different and belong both to the same batholith; that is to say, they present dif-
ferentiates of one and the same original magma, very probably. We have found
several rocks, which lie petrologically between the normal quartz-diorite and the

All these rocks contain hornblende and some of them also biotite; quartz may
be wanting here and there. A transition between quartz-hornblende-diorite and
homblende-augite-diorite can be seen in the rock A32—D 11944, described on
p. 58; these two rocks seem to be of the same age; at least, no contact-phenomena
are present here.

Hence, we can conclude that the dioritic and gabbroic rocks are closely
related and that they belong to the same batholith. We cannot accept, however,
that the diorites and the gabbros are of the same age, for the gabbros of the
Sumpina- Matividiri- Bushiribana- massive have been injected by diorite magma
and have been metamorphosed by this magma. So, there must be a difference in
age, probably a small one. The gabbros must have consolidated before the
diorites, so that the diorite magma could attack the former rocks.

There is a strong geological resemblance between these gabbros and the
hooibergite-rocks. In accordance with the latter and with Daly (12) we can consider
the gabbros a chilled roof-phase (contact-phase) in the batholithic chamber.
This agrees with the occurrence in the batholith outcrop. The gabbros have
chiefly been found in the northern and northeastern parts of the outcrop, that
is to say, in the highest parts of the batholith. Yet, they border but here and
there on the older formation, f.i. in the Matividiri and in the Seroe Crystall
(compare with the occurrence of the hooibergite-rocks).

The gabbros and the gabbro-diorites of the Bushiribana-Matividiri-Sumpina-
massive can be clearly distinguished from the dioritic rocks, which lie onthesouth-
and west-side of this massive. The diorite magma and its differentiates intruded
into the older gabbroic rocks, which must not have been quite consohdated at
that time (transition-rocks between the gabbro and the diorite came into being
here and there). Yet, the intruding magma consolidated in many cases as true dikes
in the gabbro-massive; these dikes are not so very sharply bordered on the invaded
rocks. In many places fragments of the gabbroic rocks have been taken up by the
intrusive magmas.

The intruding magmas caused a certain exomorphic contactmetamorphism
in the gabbro-rocks. Here and there the contactzone is rather wide because of a
strong injection with dioritic material. In other places the width only seems to

be very great thanks to the low dip of the contact-plane; the diorite here underlies
the gabbro-massive.

and the Diorite (northwest-foot of the Matividiri): The contactzone here has a great
width and its contactplane probabty lies about horizontally, so that it cannot be said which
of the two kinds of gabbro (the hypersthene-augite-gabbro or the augite-gabbro) has come
into contact with the diorite magma. The gabbros have strongly been altered into uralite-
gabbros or into transition-rocks between the latter and the diorites.

A 455—D 12531 probably is a contactmetamorphic uralite-gabbro. It has a gabbroic
texture and consists of plagioclase and hornblende, in about the same amount. The plagio-
clases are prismatic albites. The hornblende is green; only a few crystals look undivided and
have one and the same extinction, at least for their greater part (primary hornblende).
Far the greater part of the hornblende occurs as diverse-granular and -fibrous aggregates,
which show a crystal-shape and which probably represent paramorphisms of hornblende
after pyroxene. The individuals of the hornblende aggregates here and there are intergrown
and contain many quartz-bubbles. Others, however, are small and idiomorphic crystals
with a normal hornblende-cleavage; the latter very probably are new-made crystals. Magne-
tite especially occurs together with chlorite. A few yellow, primary-looking epidote crystals
especially occur near and with ore.

A 456—D 12532 is a mediumgrained, contactmetamorphic uralite-gabbro with a dike
of quartz-biotite-diorite (or biotite-diorite-aplite). The gabbro is more hypidiomorphic-
Rranulose than gabbroic, and consists of plagioclase, hornblende and quartz. The average
composition of the plagioclases is andesine. The hornblende occurs in the same way as in
D 12531. Biotite has been almost totally changed. The quartz does not contain fluid-inclu-
sions in a narrow peripheric zone. Although this gabbro is not sharply bordered on the dike-
rock, the transition is quot;abruptquot;. The dike-rock is a quartz-biotite-diorite or a biotite-diorite-
aplite; it has an almost aplitic texture and consists mainly of quartz and plagioclase (oligo-
clase-andesine to albite), less of altered biotite and hornblende. Hornblende is rare in the
section and seems to have been taken up from the gabbro; macroscopically we see more
crystals.

A 457—D 12533 presents a dike of quartz-hornblende-biotite-diorite in strongly altered
gabbro. The sample consists of two parts; a part, rich in quartz and poor in hornblende, and
another, poor in quartz and rich in hornblende. Under the microscope we see the same parts;
the former is the dike-rock, the latter is the altered gabbro which contains more plagioclase.
For the rest, the two parts are about the same and merge gradually. The texture is hypidi-
omorphic-granulose. The plagioclases have been totally albitized. The hornblendes of the
dioritic part are normal. Those of the gabbroic part are irregularly prismatic to granular and
especially arranged in groups; many individuals contain numerous quartz-bubbles; here and
there also new-made crystals occur. Biotite has been totally changed. The fluid-inclusions
of the gabbro quartzes occur in the centre and not in a narrow peripheric zone. Magnetite,
here and there leucoxenic (titanomagnetite), occurs more in the gabbro than in the diorite.

The rock 135*, sampled by Martin near Bushiribana, presents a hornblende-augite-
gabbro in contact with quartz-hornblende-biotite-diorite; the crystals of the two rocks work
in with and between each other. Contact-phenomena are the rather strong uralitization and
chloritization of the pyroxene; here and there small, new-made hornblende crystals occur in
the uralite aggregates. The plagioclases in the neighbourhood of the hornblende have been
almost totally epidotized.

Hence, as well as the contactmetamorphic uralite-diabases these contactmeta-
morphic gabbros contain new-made hornblende crystals. Their plagioclases and
biotites have more or less been altered, while the pyroxenes (orthorhombic and/or

monoclinic) do no more occur as such. The gabbros of the two latter rocks may
have been enriched with quartz.

Many of the normal, non-metamorphic gabbro (-diorites) have been sampled
near the contact. So probably, the beginning alteration of the pyroxene has come
into being under the influence of the contactmetamorphism. Gabbro-diorites still
containing augite material have also been found in contact with intruded diorite-
aplite.

Further Details about the Contact in the Field: Many of the smaller
massives of gabbro do not show clear contacts with contact-phenomena, and seem
to merge gradually into the surrounding diorite here and there. Only the large
massive Sumpina-Matividiri-Bushiribana has a fine contactzone, although locally
the gabbro borders on the diorite without visible contact-phenomena. In by far
the most places of the contactzone, however, the gabbro has been very strongly
injected by diorite, diorite-aplite and quartz. Here and there it is hybrid and
impregnated by numberless dikes and veins. The dikes have various widths, from
about 10 cm to about 1 meter; here and there they contain rounded-off or non-
resorbed gabbro fragments. These dikes do not only occur in the contactzone but
can also be found here .and there in the massive, f.i. on the top of the Matividiri.
The porphyrite- and lamprophyric dikes, which occur everywhere in the massive
(see map) cannot be considered as contact-dikes.

Some of the diorites contain a rather large amount of potashfeldspar, so
that they must bear the name granodiorites. In general, however, they .show the
same properties as the common quartz-diorites.

These granodiorites are rare, and they gradually merge into the normal
quartz-diorites. They do not form distinct massives in the batholith, as far as
we can see.

In A 70—D 11982 (Seroe di Poos di Noord) the orthoclase and Pmicrocline occur as
allotriomorphic crystals, in which many plagioclases lie enclosed; some of these plagio-
clases look partly resorbed. The plagioclases which are zonal oligoclase-andesines to andesines
and many hornblendes show a good idiomorphism. The great number of idiomorphic and
rounded-off plagioclases in the hornblendes is remarkable (fig. 14).

D 6175 (hills N of Savaneta) contains much quartz; and its potashfeldspar is orthoclase.
The plagioclases are non-zonal albites toalbite-oligoclases. Moreover, there occur some masses
of fibrous chlorite with epidote and leucoxenic strings, and a group of titanomagnetite with
apatite, chlorite and epidote.

Some of the rocks which are to be described in this chapter present types
intermediate between biotite-granodiorites and biotite-granites, dependent on
the proportion of the amount of lime-soda-feldspar and of potashfeldspar. Since
however, these intermediate rocktypes contain biotite as dark mineral, and since
the above-described granodiorites contain hornblende, it seems better to put the
intermediate rocktypes in the group of the biotite-granites. Only in one rock
(D 11980), belonging to those intermediate rocktypes, a very little hornblende as
non-idiomorphic crystals occurs as a second dark mineral.

Samples: A63—D 11975; A64—D 11976; A65—D 11977; A66—D 11978; A 67—
D 11979; A68—D 11980; A 69—D 11981; A 71—D 11983.

Macroscopically the granites are lightcoloured rocks, finegrained, rarely fine- to medi-
umgrained. Their quartzes have a brown or yellow colour; their feldspars are white, and the
biotite occurs as black and lustrous plates. A 63 shows an orbicular structure.

Microscopic description; The texture is holocrystalline, hypidiomorphic-granulose. The
main constituent minerals are potashfeldspar, plagioclase, quartz and biotite. The amount
of feldspar is about the same as that of quartz. The amount of biotite is rather small, and
in some rocks very small. In most of the granites the amount of lime-soda-feldspar is greater
than that of the potashfeldspar, or both amounts are about the same. In a few rocks the
amount of plagioclase is smaller than that of potashfeldspar.

The plagioclases are more or less idiomorphic, and some of them possess resorption-
holes filled up with quartz or potashfeldspar. Most of them have a zonal building, often with
recurrence-effects. In some rocks the resorption-effect as described in D 11963 (see diorites)
is clear. The average composition is oligoclase; the most basic cores are oligoclase-andesine;
the most acid peripheric zones are albite-oligoclase. A few myrmekitic intergrowths occur;
mostof them are bordered by potashfeldspar, but a single plagioclase in D 11978 is myrmekitic
against quartz. In D 11980 and D 11981 sub-granophyric intergrowths of plagioclase and
quartz may be due to a strong resorption-action of quartz-liquid in plagioclase.

Potashfeldspar occurs as dusty and allotriomorphic crystals, which wholly or partly
enclose the idiomorphic or hypidiomorphic plagioclases. Here and there the extinction is an
undulose one. In most of the granites the potashfeldspar is microcline, orthoclase, microcline-
microperthite and microperthite. In D 11983 the transition of microperthite into normal,
twinned plagioclase is very clear, and shows that the lime-soda-feldspar in the microperthite
is the same as that outside the microperthite (fig. 15).

The quartz is partly present as allotriomorphic individuals between the more or less
idiomorphic plagioclases and the non-idiomorphic potashfeldspar, partly as more or less
idiomorphic crystals in the allotriomorphic potashfeldspar. The allotriomorphic quartz must
be younger than the plagioclase and must have crystallized at about the same time as the
potashfeldspar (in D 11981 there may be a sub-micrographic intergrowth between quartz
and orthoclase). The idiomorphic quartz must have crystallized before the potashfeldspar
and shows here and there resorption-holes. filled with potashfeldspar. Some quartz crystals
even show idiomorphism with regard to plagioclase in D 11979. The idiomorphic quartzes
are wanting in a few rocks (f.i. D 11976 and D 11977). In D 11975 and D 11976 the quartz
especially occurs as rather small grains along the borders of the potashfeldspar individuals
The quot;Streifenquot; of an idiomorphic quartz in D 11983 show a difference in refraction. Limonite
occurs along fissures and moreover as very small and yellow films.

The shape of the biotite crystals commonly is tabular; they are idiomorphic or not.
Here and there plagioclases occur as idiomorphic crystals in the biotite. The biotite crystals
are rather big or small ones. They partly occur in crystal-groups. The very small crystals
occur accumulated in aggregates. — Muscovite is present in a very small amount or it is
wanting. Part of the plates occur (as primary minerals) enclosed in the plagioclase, in D 11977
especially along the borders of the biotite.

Apatite occurs as very small prisms in the quartz, the feldspar and the biotite. — A
very few crystals of zircon lie enclosed in biotite and quartz (D 11977, D 11983).—- Titanite
has been found only in D 11980 in the close neighbourhood of biotite (secondary or primary?)
— Magnetite is a common mineral, and can be found in the close neighbourhood of biotite'
partly in.it; or it occurs independently of this mineral, but then together with epidote Thé
magnetite may be titanomagnetite when accompanied by Pleucoxene.

Some epidote crystals, lying enclosed in biotite, may be primary epidotes (D 11977
D 11978, D 11979, D 11981). In D 11977 and D 11979 (fig. 16) this epidote occurs as follows:'
wholly or partly enclosed by biotite; idiomorphic, prism-shaped; with or without a good
cleavage; slightly pleochroitic from colourless to yellowish, yellowish-green or lightgreen-
high mterference-colours (abnormal or not); extinction according to the cleavage-planes 0°
(in D 11979 this epidote shows Presorption-holes against quartz). - Chlorite: D 11983 contains
some vermicular chlorite. — Calcite occurs as very small and narrow veins in D 11975.

The granites occur here and there in the bathohth and seem to merge gradually
into the quartz-diorite. So, they do not form distinct massives like the gabbros
f.i. and are very probably of the same age as the diorite. They crop out here and
there as „Felsenmeerequot;, f.i. the granite of the large outcrop just W of the Hooibw-g
(see the map). Several granites have been collected and observed W of the Hooi-
berg; moreover, they have been found near Santa Cruz, S of Kudawecha, W of
Seroe di Poos di Noord, near Seroe Compa and SW of Rincon (SE-Aruba).'

The dike-rocks which will be described here have about the same compo-
sition as the plutonic rocks in which they intruded, although they are younger.
They are different types of dike-diorites, dike-granodiorites and dike-granites.
In fact, the latter two kinds of rock are no true contemporaneous dike-rocks
where they occur in the diorite, but still all of their representatives can be reckoned
among this group. Those rocks have been added as well, which occur as dikes in
the older differentiates of the batholith, f.i. in the hooibergite-rocks.

Quartz-hornblende-diorite (A 282—D 12293; A 285—D 12296; A 324—D 12315.
D 12316; A 326—D 12318; A 327—D 12319; A 357—D 12335; A 359—D 12337; A 372-
D 12341; P 81—D 6546; P 99—D 6178; P69—D6180): Macroscopically these rocks are
fine- to mediumgrained. and light- or darkcoloured. Some of them look more lamprophyric
than dioritic. The diorite-dike of A 326 shows a flow-structure, the hornblende crystals
lying roughly parallel to the dike-borders.

Microscopic description: The texture is more or less hypidiomorphic-granulose, hypid-
iomorphic- to allotriomorphic-granulose, or pan-allotriomorphic-granulose. Hence, a
sequence of crystallization cannot be recognized in all the rocks. In those rocks where it is
wanting more or less, the quick coohng of the dike-magma may be the cause. The main constit-
uent minerals are plagioclase, hornblende and quartz. The plagioclase takes up more room
than or about as much room as the hornblende. Quartz is quantitatively the second or the
third mineral.

In the rocks with a hypidiomorphic-granulose texture not all the plagioclases are quite
idiomorphic (contemporary crystallization or partial resorption?). The composition of the
plagioclase is oligoclase-andesine, rarely oligoclase or albite. In D 12315(16) some albites
possess colourless, isotropic spots with a higher refraction than the surrounding plagioclase
material. The crystals in D 12296 and D 12319 are long-prismatic to lath-shaped.

The hornblende commonly is regularly distributed but it occurs in groups as well.
It is the normal green hornblende; several of the crystals in D 12335 have darkgreen cores.
The crystals are prisms, partly idiomorphic with regard to quartz and plagioclase. Quartz-
bubbles occur in some of them.

Quartz is allotriomorphic. Locally, narrow and irregular strokes of an albitic feldspar
occur in some quartzes of D 12315 (16): filling of fissures by albitic material; the plagioclases
have been totally albitized in this rock.

Apatite, grains of titanite, here and there especially tied to hornblende and ore, magne-
tite and titanomagnetite are accessory.

These rocks have been found as dikes in the diorite batholith and in the hooibergite-
massives.

Dike-quartz-hornblende-diorite invaded by another dike-quartz-hornblende-
DioRiTE (A 283—D 12294; S of Santa Cruz): The sample shows a darkcoloured, finegrained
rock, with a narrow dike, about 3 mm. wide, of a normally dioritic rock.

The darkcoloured rock mainly is a plagioclase-hornblende-rock with locally some
quartz. Plagioclase (oligoclase-andesine to andesine) and hornblende, green to brownish-
green, constitute a pan-idiomorphic-granulose texture.

The dioritic rock, occurring as a narrow dike in the dike-diorite described above, is
mainly a plagioclase-quartz-rock, with some hornblende crystals, and coarser grained than
the described rock. Its texture is rather hypidiomorphic-granulose, and the oligoclase-
andesines show a prismatic development. Quartz is abundant. It is remarkable that apatites
only occur along the borders of the dike.

Hence, the distinction between the darkcoloured diorite and the lightcoloured one is
clear. Nevertheless, the rocks do not sharply border on each other; the crystals on both
sides normally work in with and between each other.

Quartz-bearing hornblende-diorite dike with an inclosed fragment of quartz-
hornblende-diorite (A 286—D 12297; N of Spaansch Lagoen): The enclosed fragment
is an orthoclase-bearing diorite. Its plagioclases have been strongly altered; there is a clear
connection between the albitization and the polysynthetic twinning. The original composition
probably was oligoclase-andesine. The hornblende too is little altered.

The dike-diorite mainly consists of plagioclase and hornblende; quartz is of a minor
importance. Plagioclase and hornblende constitute a pan-idiomorphic or pan-allotriomor-

phic-granulose texture The plagioclases are albite-oligoclases (albitized ?), only a little altered

The crystals on both sides normally work in with and between each other, so that theTuvIrd

diorite cannot have been quite consolidated at the time of the intrusion. A certaifmrmatfc

(P 103-D 6562, dike in hooibergite of the Hooiberg): The texture, being about hypidiomor
phic-granulose, points to a dioritic rock, but the richness in quartz and the vSy sTa ;
amount of hornblende point to a diorite-aplitic rock. The plagioclases are otocSsesld
oligoclase-andesmes. Beside some small individuals no fresh hornblende L preset Some
epdote masses, irregularly or more or less prism-shaped, may have origmated from hoTn!

The sample is a finegrained feldspar-hornblende-rock, Le and th ^e wi\h qu'^^^^^^^^^^

eldspar and hornblende quot;phenocrystsquot;; globular inclusions of a lightcotu^S apmic
looking rock can be distinguished as well.nbsp;quot;gntcoioured, aplitic-

In the slide the normal, darkcoloured rock and a part of a liehtcolourpHnbsp;. k

seen. The rocks merge gradually. The difference is quite clear, ftnk to th^^^^^^^^^ in'
he quantity of hornblende. In the darkcoloured rock a small quartz globule occTrs wi h
fluid-inclusions in planes and without a special rim. The normal darLoloured d on e is
pan-idiomorphic-granulose and consists of plagioclase, hornblende and rather mlh Tuart

lo e,the plagioc ases being more lath-shaped. Plagioclase (oligoclase-andesine asL heSrlT
Ti We aTnbsp;and hornblende (as small prisms) are'he main constLent iSntat

T^anite and small groups of epidote are present here, but are wanting in the darkcZred

Hornblende-diorite (A 358-D 12336; dike in the hooibergite of Seroe Tres Kabees^ •
A plagioclase-hornblende-rock without quartz, strongly altered, with alb!feed p aSc^

Quartz-hornblende-biotite-diorite (A 74—D 12042- iust nw of u n
The rock is hyp.d,omorphic.g„n„.ose and Lsists of oUgod^to o^^ lastfdquot;^^^^^^^^^^^

the second p.ace o, hornblende and quartz, in the third p.ac! of al,.ost wh'X quot;bSit quot;

a darkcoloured, finegrained hornblende-feld par-rock as a dike i^a Jtcolor.d quot;
grained diorite. The latter is a normal quartz-Lnblende-bioJ^dL t
b otite; i^ts plagioclases are oligoclase to oligoclase-andesine. The dike-dioritf r!dr i^horn

towards the lathshape, and vary m composition from oligoclase-andesine tn Inhr.H.. q
po^^hfeldspar is present. Several hornblendes contain qulrtz-bub£. Th^^^^^^^^^^
almost completely altered. The difference between the two rocks is clear thanks to tC
difference in size of the crystals and in quantity and distribution of the ho Xde tL
rocks do not sharply border on each other.nbsp;uurnoienae. ine

Hornblende-biotite-diorite (A 284—D 12295; Sabana Grandi): The texture is pan-
allotriomorphic- to pan-idiomorphic-granulose. It consists of oligoclase-andesine, many small
hornblende prisms with here and there quartz-bubbles and some biotite.

Hornblende-granodiorite (A352—D 12330, A353—D 12331; dikes in hooibergite
of the Seroe Bientoe): The texture is hypidiomorphic- to allotriomorphic-granulose. In
D 12330 the texture, being on the whole hypidiomorphic-granulose, is pan-allotriomorphic-
granulose and finer grained near an enclosed hooibergite fragment. The plagioclases are
oligoclase-andesines. Potashfeldspar occurs less than plagioclase, and is allotriomorphic; the
boundary between plagioclase and potashfeldspar is not quite straight everywhere (resorption
and/or contemporary crystallization). The potashfeldspar occurs in D 12331 as narrow rims
around and between the plagioclases. In D 12330 it is only microcline; in D 12331 orthoclase,
microcline and microcline-microperthite. It is very remarkable, that the potashfeldspar in
D 12330 does not occur in the aplitic part near the countryrock (see above); possibly the
potashfeldspar could not crystallize here because of the very quick cooling. Hence, this part
of the rock has the composition and the texture of a dioritic aplite. Hornblende only occurs
as a few and small prisms. Quartz is the second mineral. Some crystals in D 12331 are
idiomorphic with regard to potashfeldspar. Apatite, rare magnetite and several idiomorphic
titanite crystals and grains are accessory.

Biotite-granodiorite (A 77—D 12045; near Seroe Plat): This rock very nearly ap-
proaches the dike-granites. The texture is hypidiomorphic- to allotriomorphic-granulose.
Potashfeldspar occurs in about the same quantity as plagioclase; it is represented by dusty
crystals of orthoclase, microperthite, microcline and microcline-microperthite. Many of the
oligoclase-andesines are idiomorphic with regard to quartz and potashfeldspar. Some of the
quartzes are idiomorphic with regard to the potashfeldspar. Several granophyric inter-
growths of plagioclase and quartz can be found. The biotite is brown and green. Magnetite,
apatite.

Biotite-granite (A 78—D 12046, N of Salinja Cerka; A 79—D 12047, Seroe Tres
Kabees): The rocks are finegrained, and hypidiomorphic-granulose. The potashfeldspar occurs
as orthoclase, microcline, microperthite, microcline-microperthite. They are big, allotrio-
morphic crystals which enclose in a poikilitic way earlier crystallized and idiomorphic
plagioclases. quartzes and also biotites; partly these enclosed plagioclase and quartz crystals
have resorption-holes. The composition of the plagioclase core is oligoclase-andesine, that
of the peripheric zones albite-oligoclase to oligoclase. Quartz occurs as idiomorphic crystals
in the potashfeldspar and as allotriomorphic individuals between the plagioclases. Hence,
there are two different kinds of quartz, that did not crystallize at the same time. The biotite
occurs as separate plates or in groups and streaks; the latter locally lie around idiomorphic
plagioclases. Magnetite and apatite are common. Some epidotes, enclosed in biotite, may be
primary. D 12047 contains moreover some titanite grains and zircons. In D 12046 some grains
of spinel are tied to the biotite.

The dikes have not been indicated in the geological map. They occur as
normal dikes, not very long and with a width, which is not greater than 3 meters,
generally, and which is here and there but a few dm. N of Salinja Cerka a long,
granitic dike occurs, locally more than 3 meters wide and cropping out as small,
roundish blocks; the dike, N 70E,lt;-has been faulted in two places, so that the

eastern parts have been removed a few meters towards the north with regard to
the western part.

■ The strikes are varying; several dikes strike N 100 E and N 140 E. The
dips are vertical or very steep, rarely less steep.

This kind of dikes is not so widespread as the leucocratic dikes. Besides in the
contactzones between diorite, hooibergites and gabbros the contemporaneous
dikes have only been observed in the batholith outcrop in the northwestern half
of the island. On an average, the dikes occur regularly distributed in this outcrop.
It IS remarkable, however, that most of the dioritic dikes have been observed in
the southwestern zone of this outcrop, whereas most of the granitic dikes occur
in the northern and northeastern parts.

Younger representatives of the magmatic sequence in the diorite bathohth
are, amongst others, those dike-rocks, which have a composition, not so very
different from that of the plutonic rocks of the bathohth: the porphyrites and the
vmthtes. As will be shown here below, transitional rock-phases between diorite
and porphyrite and between porphyrite and vintlite have been found too and
these rocks prove that the different rock-types are all products of one and the
same magma.

The porphyrites and the vintlites occur as dikes in the diorite, but also in
a great number in the older rock-system; the latter must have their source in
the bathohth, which lies in the underground of these older rocks. The dikes also
cross the contactzones between the older rocks and the diorite. Especially the
gabbro-massive of Matividiri contains many dikes.

The rocks occur in the landscape as distinct dikes, a great number of which
are very long and wide; the dikes can be clearly distinguished from the rocks
in which they intruded, because of their shape and colour; in general, the dikes
do not occur as elevations.

By far the most of these rocks are diorite-porphyrites. These diorite-porphy-
rites can be divided into two groups: quartz-hornblende-diorite-porphyrites
(constituting the bigger group) and hornblende-diorite-porphyrites (the smaller
group), dependent on the occurrence of quartz and/or hornblende phenocrysts. How-
ever on the whole, there is no great difference between these two groups More-
over, two aberrant porphyrites (A 228-D 12248; and D 860) and one rock, being
transitional between porphyritic quartz-hornblende-diorite and quartz-horn-
blende-diorite-porphyrite (A 220—D 12240) have been found.

The groundmass of the porphyrites is finegrained to aphanitic. The maximum size of
the plagioclase phenocrysts is about 7 mm, that of the hornblendes about 15 mm that of
the quartzes 5 mm.

The transition-rock between diorite and porphyrite (A 220—D 12240) is a dike
rock, transitional between porphyritic quartz-hornblende-diorite and quartz-hornblende-

diorite-porphyrite (north-foot of Matividiri). Tlie rock is a dioritic one, in which some feldspai s
have a more or less phenocrystic appearance. Properly speaking, only some plagioclases
have developed as phenocrysts with a rather good idiomorphism, zonally built and partly
with recurrence-resorption; oligoclase-andesine. These phenocrystic plagioclases lie in a
hypidiomorphic-granulose-textured, dioritic quot;groundmassquot; of zonal plagioclase, hornblende,
quartz, magnetite and apatite. Here and there quartz and plagioclase occur in granophyric
intergrowth.

Quartz-hoknblende-diorite-porphyrites (A 221—D 12241; A 222—D 12242; A
224—D 12244; A 225—D 12245; A 226—D 12246; A 227—D 12247; A 231—D 12251; A 232—
D 12252; A 233—D 12253; A 235—D 12255; A 238—D 12258; P 83—D 6172 and D 6548;
P 84—D 6173): In some of these porphyrites hornblende phenocrysts can no more be found
having been changed into several secondary alteration-products. In one rock even (P 84—
D 6173) hornblende as well as its alteration-products are totally absent. Still, it seems admis-
sible to put these rocks into the quartz-hornblende-diorite-porphyrite group.

Macroscopically many of the rocks show a green to grayish-darkgrayish (to black)
groundmass, with feldspar, quartz and hornblende phenocrysts. Other rocks look more fine-
grained-granitic and dioritic than porphyritic, and do not show the phenocrysts so clearly.

Microscopic description: In a great part of the rocks the groundmass takes up more
room than the phenocrysts; in other rocks they are about equivalent. And even in one rock
(D 12255) there are more phenocrysts than groundmass. The phenocrysts are plagioclases,
hornblendes and quartzes. In most of the rocks the plagioclase phenocrysts take up more
room than the hornblende phenocrysts; in others the amount of both is about the same. In
some rocks the amount of plagioclase phenocrysts is about the same as that of quartz pheno-
crysts; in most of the porphyrites, however, the plagioclase phenocrysts are more frequent,
and in many of these rocks the quartzes are only present as a few or a very few crystals. In
general, quartz occurs in a smaller amount than hornblende. The above-mentioned variations
in the frequency of phenocrysts do not show any regularity. D 12258 and D 12242 show
hornblende and plagioclase phenocrysts, that drifted together.

Plagioclase phenocrysts: The plagioclases show a partial, seldom total alteration,
especially the cores. Calcite rarely occurs. The plagioclases of a part of the porphyrites have
been totally albitized. In some of the plagioclases of D 12253 more or less brownish-dusty
spots are to be seen, isotropic and with a refraction, less than about 1,535: opal. The
phenocrysts are idiomorphic or not. The latter are for the smaller part fragmentary crystals
(crystalsplinters), for the greater part rounded-off phenocrysts. These rounded-off (in a few
cases also partly resorbed) crystals owe their shape to the magmatic resorption after the
crystallization of the phenocrysts and before that of the groundmass-magma. In D 12242
some plagioclases have drifted together and are grown together. In D 12247, D 12253 and
D 12255 the phenocrysts are not sharply bordered on the groundmass, that is to say, the
crystals of the groundmass (especially the quartzes) work in with the phenocrysts; hence,
these phenocrysts probably continued to crystallize during the consolidation of the ground-
mass. The plagioclases more basic than albite are in general zonally built, often with recur-
rence-zones (repeated recurrence with resorption-effects, in most cases). The average compo-
sition of the unaltered plagioclases ranges from oligoclase to andesine, rarely to labrador. In
D 12241 many very small plagioclase phenocrysts (zonal laths) occur beside bigger ones.
Probably, the former represent a second generation of phenocrysts.

Hornblende phenocrysts: They are prisms of normal green hornblende. The crystals
are more or less idiomorphic; rarely fragmentary, frayed, or rounded-off and partly resor-
bed. In D 12244 most of the hornblendes show a paramorphism into fibrous secondary horn-
blende. As a particularity it must be mentioned that most of the phenocrysts in D 6172 and
D 12247 are surrounded by a rim of small biotite plates, which probably are primary. In
accordance with the total albitization of the plagioclase phenocrysts of D 12242, D 12245,
D 12251, D 12255, the hornblende phenocrysts have been totally altered, whereby the prism-
shape has been more or less preserved. «■

Quartz phenocrysts: Some phenocrysts are still idiomorphic; most of the quartzes are
strongly rounded-off and partly resorbed. D 12247 shows plagioclase and hornblende
phenocrysts m a groundmass, the latter being enclosed itself in a resorption-hole of a quartz
Fragmentary phenocrysts rarely occur. By far the most of the quartzes in D 12247 D 12253
and D 12255 are not sharply bordered on the groundmass (nor the plagioclase phenocrysts
m these rocks either, see above!), the crystals of the groundmass (especially the quartzes)
working m with them. Probably also these phenocrysts continued to crystallize during the
consolidation of the groundmass. D 12253 contains some big quartzes, which are no true
phenocrysts and which enclose some plagioclases in a.dioritic way; plagioclase phenocrysts
probably have been enclosed here in very big quartz phenocrysts. - In D 12252 and D 12241
irregularly shaped quartz occurs enclosed in the core of a hornblende phenocryst; moreover
quartz grains can be found in the core of a plagioclase phenocryst in D 12252

The groundmass is holocrystalline. Two kinds of groundmass-texture can be distingu-
ished: the allotriomorphic-granulose one (here and there with affinities to the micro-granitic
texture) and the pseudo-spherolitic texture.

The following types of groundmass have been observed: -D 12253: allotriomorphic-
granulose groundmass of quartz and plagioclase (probably oligoclase). -D 12245- as in
D 12253; the plagioclases, however, are albitic. -D 12255: as in D 12245; moreover some
chlorite probably originated from small biotite plates. -D 12252: as in D 12253' moreover
small biotite plates. -D 12244: as in D 12253; moreover very small hornblende prisms
(vmthtic quartz-hornblende-diorite-porphyrite). - D 6173: as in D 12253; moreover very
small biotite and chlorite plates ; Phornblende is very rare. -D 12241: about as in D 12253-
however, the one part of the groundmass, an aggregate of grainy oligoclase with a very little
quartz, merges into a finer grained part which seems to consist only of dusty oligoclase-
moreover, numerous very small chlorite scales occur. -D 6172, D 12247: as in D 12253' many
of the plagioclases are zonal and more or less idiomorphic; nevertheless, the texture is more
allotriomorphic-granulose than microgranitic. Moreover, small biotite plates. -D 12242' the
groundmass is for the smaller part as that of D 12245, and consists for the greater part of
radiant pseudo-spherolites (H. Rosenbusch (37) p. 353); the latter are sectors of globules, and
consist alternately of fresh quartz radia and dusty albite radia; these radia branch out in an
irregular way or like feathers; moreover, these pseudo-spherolites merge into granophyric
mter^owths here and there. They are especially attached to quartz phenocrysts.-D 12246:
as m D 12242; the pseudo-spherolites seem to be eutectic-granophyric intergrowths. -D 12251
D 12258: as in D 12242; the pseudo-spherolites are more (true pseudo-spherolites) or less
(granophyric textures) regularly built.

Accessory minerals: Apatite occurs in phenocrysts and groundmass. Magnetite occurs
m a varying amount. In D 12241 and D 12244 there are rather big grains, and very small
ones in the groundmass; the big grains may constitute the first crystallization-phase (quot;pheno-
crysts ), and the small ones the second crystallization-phase of the magnetite material
( groundmassquot;). Titanomagnetite, titanite, zircon, Pprimary epidote and biotite rarely can
be found.nbsp;''

Hornblende-diorite-porphyrites (A223—D 12243' A 229—D 12249- A 230—D
12250; A234-D 12254; A236-D 12256;A237-D 12257; A 239-D 12259): On the whole
these rocks are similar to the porphyrites with quartz phenocrysts.

The phenocrysts are plagioclases and hornblendes. In D 12250 and D 12259 the plagio-
clase phenocrysts are not sharply bordered on the groundmass as in some of the quartz-
diorite-porphyrites.

Hornblende phenocrysts: In D 12254 a single hornblende has a rim of small biotite
plates. Hence, where chlorite lies as a rim around other hornblendes or hornblende cores.
Tnbsp;f7o® quot;nbsp;originated from biotite, that surrounded the hornblende,

in igt; 12243 the phenocrysts are brownish-green, well-idiomorphic hornblendes with an ill-
developed cleavage. D 12249 only contains a single, ill-preserved hornblende In D 12'?57

the phenocrysts have been altered for the greater part, partly with preservation of the
prism-shape. In D 12250 and D 12259 prism-shaped, irregularly shaped masses and zones
of epidote and chlorite (with titanite) probably originated from hornblende phenocrysts. The
chlorite is radiant-fibrous with steelblue or greenish-brownish interference-colours. There
is a connection between this alteration and the alteration and the distortion-phenomena in
the plagioclases of these rocks.

Groundmass: Three kinds of groundmass can be distinguished: the allotriomorphic-
granulose-textured, the micro-granitic, and the pseudo-spherolitic quartz-plagioclase-
groundmass.

D 12259: allotriomorphic-granulose; quartz and albitic plagioclase. —D 12256: as in
D 12259, plus very small scales of chlorite. —D 12243: as inD 12259, plus numerous and very
small scales of Pchlorite and Ptitanite. —D 12250: the groundmass is partly as that of
D 12256, and consists partly of radiant pseudo-spherolites as in the quartz-hornblende-
dioriteporphyrites; these pseudo-spherolites are especially attached to plagioclase pheno-
crysts. —D 12257: microgranitic; more or less lath-shaped albites and allotriomorphic
quartz; the former, however, are not everywhere idiomorphic with regard to the quartz-
—D 12249: as in D 12257; green biotite is a common mineral, partly chloritized. —D 12254:
the groundmass is partly like that of D 12249; the plagioclases, however, are probably
oligoclases. Many radiant and globular pseudo-spherolites occur scattered in it; they are
here and there attached to phenocrysts.

The main difference with the above-described porphyrite-group is the lack of quartz
phenocrysts. Probably, the quartz phenocrysts have been present in the magmatic phase,
but could not remain as such and have been assimilated again by the liquid. At all events,
quartz is abundant in the groundmass. i)

The two aberrant porphyritic rocks are the following: D 860 presents a spherolitic
quartz-porphyrite with a reddish-brown groundmass. The latter contains quartz and oligoclase
phenocrysts. In one place a curious intergrowth of both kinds of phenocrysts can be seen
(fig. 17). The groundmass consists of small chalcedony-spherolites, working in with each
other, between which lamelled laths of acid plagioclase occur . Groundmass and plagioclase
phenocrysts have been strongly infiltrated by limonite.

A 228—D 12248 presents a strongly altered porphyrite, without hornblende, found
just N of Santa Lucia. Sericite, epidote and chlorite occur in large masses and as irregular
zones through the whole rock. The small quartz crystals of the groundmass work in with the
albite phenocrysts.

Petrogenetically these rocks are transition-rocks between the diorite-
porphyrites and the lamprophyric rocks.

The Aruba vintlites distinguish themselves from the Aruba diorite-porphyri-
tes, mainly, by the smaller amount of quartz in the groundmass, by the greater
development of lath-shaped plagioclases in the groundmass, and by the richness
in dark minerals (especially hornblende) in the groundmass. The relation, however.

1)nbsp;J. H. Kloos (25) described several (quartz-) hornblende-dioriteporphyrites, sampled
by Martin. Kloos abusively described the totally epidotized and chloritized hornblende
phenocrysts in 117b as augite phenocrysts (p. 64); orthoclase is wanting (compare with the
rock A 222—D 12242; both rocks have been sampled in the same place near Fontein).

2)nbsp;According to H. Rosenbusch (37) p. 356: quot;Bei Verkieselung von Quarzporphyren
quot;und Lipariten füllen sich die Grundmassen oft mit radialstrahligen Chalcedonkugelnquot;,' the
original groundmass of this porphyrite seems to have been partly siUcified.

between the quantities of plagioclase and hornblende phenocrysts is generally
about the same in both porphyritic rocks.

The vintlites can be divided into several groups: the vintlites with plagioclase,
hornblende and quartz phenocrysts; those with plagioclase and hornblende
phenocrysts; those with plagioclase, hornblende and pyroxene phenocrysts;
moreover, there have been found a single vintlite with plagioclase, hornblende!
pyroxene and quartz phenocrysts, and a single one with hornblende, altered-
pyroxene and quartz phenocrysts. - A rock will be described as well which is a
transition-rock between quartz-hornblende-dioriteporphyrite and vintUte.

The groundmass of the vintlites is finegrained to aphanitic. The plagioclase pheno-
crysts reach a maximum size of about 15 mm, the hornblendes 19 mm, and the quartz-
es 7 mm.

Transition-rock between quartz-hornblende-dioriteporphyrite and vintlite
(A 265—D 12264; W of Andicouri in the gabbro massive): The phenocrysts are plagioclases
(andesine to labrador), less hornblendes and a very few quartzes. Here and there they have
drifted together, while also flow-structures can be seen. The quartz phenocrysts are totally
rounded-off. Fig. 18 shows a phenocryst with a round-bordered quartz-centre, around which
the form of a slightly visible and fragmentary crystal can be distinguished. The part of this
fragmentary crystal outside the round quartz-centre is mainly composed of quartz, with the
same extinction as the centre; however, beside this quartz, this part contains small plagio-
clase laths and (less) small biotite plates, both of the groundmass. and moreover pseudo-
spherolite-like parts here and there. As to this quartz crystal we can probably conclude, that
the original phenocryst has been partly resorbed (unto the round central part), and that
afterwards the quartz of the groundmass crystallized (together with the other groundmass
components) around and with the same orientation as the quartz of the resorbed phenocryst,
thus creating the fragmentary limitation in the surrounding groundmass.

The groundmass consists of small laths of plagioclase (lamelled; zonal; probably about
oligoclase-andesine). very small plates of green biotite (no hornblende prisms, as in the normal
vintlites!), and allotriomorphic quartz. Here and there, in the place of this quartz, the ground-
mass looks pseudo-spherolitic. i)

ifc q^artz-dioriteporphyrite. showing transitions to vintlite. found as a
ianvnbsp;(SE-point of the island); beside the small b otite plates

hornblende crysta s are present in the groundmass. which is microgranitic and
Marginnbsp;rock (120a) has been described on p. 63. Sampled by

Martin near Shete; the groundmass contains plagioclase laths, hornblende (chlorite) needles

Hornblende-quartz-vintlites (A261-D 12260; A 262-D 12261; A268-D 12267;
A 270-D 12269; A 271 - D 12270; A 272 -D 12271; A 273-D 12272; A 275-D 12274;
A 277 -D 12276; A 278 - D 12277): Macroscopically these rocks are porphyritic ones. In a
black-grayish, or darkgrayish to dark-grayish-green groundmass feldspar phenocrysts,
hornblende phenocrysts and quartz phenocrysts can be distinguished. A very thin, greenish
rim can be seen around the quartzes in A 261. A small diorite fragment occurs enclosed in
A 278. — PI. III. fig. 4.

Microscopic description: The groundmass takes up much more room than the pheno-
crysts. In general, the relative quantity of the different phenocryst-minerals is the same as
that in the quartz-dioriteporphyrites. There seems to be the following order concerning the
relations between the different phenocrysts but it is of a questionable value: the more room
is taken up by the phenocrysts with regard to the groundmass, the more quartz phenocrysts
seem to be present with regard to plagioclase phenocrysts, in general. In D 12271 the horn-
blende phenocrysts can be distinguished only with difficulty from the hornblendes of the
groundmass, the size of both being only a little different. Flow-structures (in D 12267 and
D 12270) especially occur around phenocrysts, and clearly manifest themselves by means
of the small hornblendes of the groundmass.

Plagioclase phenocrysts: As to alteration, albitization, shape, resorption, zonal struc-
tures and composition the plagioclases generally agree with those of the quartz-hornblende-
dioriteporphyrites; the composition may be somewhat more basic, the original average
running from oligoclase to labrador. A very few plagioclases of D 12270 contain numerous
microlites in their cores. The strongly rounded-off crystals in D 12269 possess dusty rims
(resorption effect). The more acid peripheric zones of the phenocrysts in D 12270 are not
sharply bordered on the groundmass; the hornblendes of the latter stick in these zones.

Hornblende phenocrysts: In so far as not altered, the hornblende is the common green
one; some of the crystals in D 12269 possess a periphery, which is a little darker green than
the central part; yet, the whole crystal has one and the same extinction. The phenocrysts
are idiomorphic prisms, rarely rounded-off. Those in D 12277 are not sharply bordered on
the groundmass. In D 12267 and D 12272 phenocrysts occur with a rim of small groundmass
hornblendes, and with many epidote grains in the close neighbourhood.

Hornblendes in several rocks have been partly or totally altered into chlorite fibrous
secondary hornblende (in D 12277 together with numerous quartz-bubbles) and epidote.
Many of them show a composed alteration. There is a connection between the alteration of
the hornblendes and that of the plagioclase phenocrysts. The possibility remains, that - at
any rate partly - the secondary hornblende originated from (is pseudomorphic after) pyroxene
and can be called uralite. This possibihty. however, is very small, taking into consideration
the total absence of fresh pyroxene and the hornblende-shape of the altered crystals.

Quartz phenocrysts. D 12260, D 12261, D 12267, D 12269, D 12271, D 12274, D 12276:
The quartzes are for the greater part rounded-off crystals, for a very small part quite round
or roundish ones; some even show resorption-holes. A small, idiomorphic hornblende (Ppheno-
cryst) seems to be enclosed in the quartz of D 12276.

Reaction-rims: a) D 12267, D 12269, D 12271 and D 12274 show narrow hornblende
reactionrims around the quartzes. In the DD with more than one quartz, only part of the
quartzes have such a rim. The rims are composed of bundles of very small and thin horn-
blende needles; these bundles lie in the quartz substance or stick partly in it. A single quartz
in D 12269 possesses a rim of chlorite, which may be altered hornblende. - 6) D 12260, D 12261
and D 12276. D 12276: a single quartz with a reactionrim (fig. 19), composed of epidote grains,
with here and there a little chlorite. D 12260, D 12261: the rims around the quartzes are
composed of small prisms and needles of monoclinic pyroxene (also of epidote or of horn-
blende?) in bundles and sheaves. Some chlorite (and calcite in D 12260) is present as well.
The crystals of pyroxene lie in the peripheric part of the quartz, or stick in the quartz sub-
stance.

InD 12270, D 12272, D 12277 the quartzes are non-idiomorphic, round, or rounded-off
and semi-resorbed, and consist of several small quartz individuals. Fluid-inclusions in planes

occur in several of them. The quartzes of D 12277 are not round, and rims are wanting- the
crystals are not sharply bordered on the groundmass (see also its hornblendes) No 'true
reactionrim can be found in D 12270 and D 12272; the small hornblende crystals of the
groundmass, however, more or less occur as a rim around the quartzes. The rim is wanting
around some quartzes in D 12270; there, the crystals of the groundmass stick in the quartz
with their free ends.

The groundmass consists of small laths of plagioclase, of small prisms of green horn-
blende, between which more or less allotriomorphic quartz occurs. In most of the rocks the
plagioclases are lamelled and simply zonal. Their original composition varies from oligoclase
to andesine. Part of the hornblendes are twinned, in so far as not altered. The groundmass in
D 12277 is very rich in quartz .Quartz seems to be wanting in the groundmass of D 12261.
In that of D 12270, beside the hornblendes, many very small biotite plates occur partly
chloritized. Many small grains of epidote occur scattered in the groundmass of several rocks
In the groundmass of D 12260 and D 12261 monoclinic pyroxenes also are present (compare
with the pyroxene rims around the quartzes!).

Accessory minerals: Apatite especially occurs in the groundmass. The magnetite gener-
ally occurs as a few bigger grains and as many diminutive ones (compare respectively with
phenocrysts and second generation); here and there the grains have a narrow rim of epidote
Titanite rarely occurs, as grains or in strings.

The hornblende-quartz-vintlites, described here, have been found exclusively in the
diorite batholith.

Hornblende-vintlites (A263—d 12262; A 264—d 12263; A 269—d 12268quot; A 276-
D 12275): On the whole, these vintlites are similar to the hornblende-quartz-vintlites, except
m the lack of quartz phenocrysts. The original, average composition of the plagioclase
phenocrysts is more basic than that of the quartz-hornblende-dioriteporphyrite plagioclases
and runs from oligoclase to labrador. In D 12263 the phenocrysts are not sharply bordered
on the groundmass. - The hornblende phenocrysts in D 12263 have been altered into chlorite
m which many small plates of browngreen biotite occur. Some in D 12262 and D 12263
contain in their cores a diopsidic pyroxene; the latter may be strongly limonitized and may
be partly twinned. Hornblende and pyroxene seem to be in intergrowth here. - The ground-
mass of D 12263 contams among the normal constituents small epidote grains and, here and
there, small browngreen biotite plates (see also above). - D 12262 contains a very few grains
of pyrite. — PI. III. fig. 3.nbsp;j- e

The vintlites described here are limited to the very northern part of the island. It is

no eworthy that A 263-D 12262 (Seroe Grandi) and A 264-D 12263 (near Druif), both

t 497 n il-^o . 'k- ^ ^«^-described hornbleLe-vintlite
A4//—u 12ol2 has been sampled in the older rocks S of Andicouri

As in the hornblende-dioriteporphyrites quartz phenocrysts could not continue to exist
crystSliJatiLn^ ^^nbsp;existence in a beginning-phase of the magma

A ^81-D 12280): These rocks show similar properties as the hornblende-quartz-vinthtes -
The groundmass takes up more room than or as much room as the phenocrysts. The latter are
plagioclases, hornblendes and pyroxenes. The quantities of plagioclase and hornblende-
pyroxene are about the same; or more ferromagnesian phenocrysts occur than plagioclase
phenocrysts; the latter, however, are the bigger crystals, the former the smaller ones

The plagioclase phenocrysts have the same shape and zonal structure as those of the '
quartz-hornblende-dionteporphyrites. The crystals of D 12279, however, are lath-shaped
composition is more basic than that of the porphyrite plagioclases, and runs
from andesine to labrador-bytownite.

Pyroxene phenocrysts are present in about the same amount as the hornblende pheno-
crysts, in D 12278. They are partly idiomorphic (short prisms), partly rounded-off (resorbed),
here and there fragmentary. The pyroxenes are very palegreen to nearly colourless diopsidic
augites, some of which are twinned. Quite-unaltered pyroxenes are wanting in D 12279.

Pyroxene and secondary hornblende. D 12273, D 12278, D 12279: Several pyroxenes
possess a more or less regular rim of hornblende and are quot;intergrownquot; with hornblende.
Probably these pyroxenes are partly uralitized, the hornblende material occurring along the
fissures of the pyroxene and being not sharply bordered on it. However, some pyroxene-
hornblende crystals may be primary intergrowths. The hornblende (secondary or primary)
in and around the pyroxene is here and there chloritized. In D 12273 some crystals with
chloritized hornblende in the pyroxene and still-preserved hornblende around it are present.
- D 12273, D 12279, D 12280: Part of the pyroxenes have been quite uralitized, whereby the
prism-shape has been preserved; the secondary hornblende is fibrous, and is partly chloritiz-
ed. There is, however, a possibility, that some of these secondary hornblendes have origi-
nated from primary hornblendes, taking into consideration the forms and the presence of
this secondary hornblende next to fresh pyroxenes. In D 12273 there can also be found
irregular masses of hornblende fibres, chlorite, some calcite and epidote, which masses
probably owe their existence to pyroxenes.

The groundmass is on the whole similar to that of the hornblende-quartz-vintlites, but
is poor in quartz. Small pyroxene prisms occur in D 12280, perhaps also in D 12273. Ortho-
clase may be present in the groundmass of D 12280. Moreover, in that of D 12273, D 12278
and D 12279 small calcite plates and epidote grains occur. Magnetite is accessory.

These hornblende-augite-vintlites (without quartz phenocrysts) only have been found
in the diabase-schist formation in the central part of the island, and especially in a region W
of Boca Prins; A 281—D 12280 has been found near and W of Boca Prins, the other three
rocks occur about 2 km. W of this Boca.

A 279, hornblende-augite-vintlite, has been collected as a quot;Salbandquot; sample of a quartz-
hornblende-dioriteporphyrite (A 238—D 12258) dike. The fact that the pyroxene pheno-
crysts only are present in the quot;Salbandquot; of this dioriteporphyrite-vintlite dike, is interesting
in connection with an observation of v. Foullon with regard to the pyroxene-vintlites,
quoted by H. Rosenbusch (36) p. 561: quot;Interessant ist die Beobachtung v. Foullon's, dass
quot;in den pyroxenfiihrenden Gängen die Diopside nach den Salbändern hin sich anreichernquot;. -
A 280, hornblende-augite-vintlite, too occurs as a quot;Salbandquot; of a dioriteporphyrite dike in
the diabase (very finegrained uralitized diabase) which has been invaded by narrow veins.

The following rock A 428—D 12513, occurring on the Seroe Kabaai, must probably be
reckoned among this hornblende-augite-vintlite group, although it does no more show
pyroxene as such. The hornblende-pyroxene phenocrysts, in about the same amount as the
albitized plagioclases, have been quite changed into an aggregate of green, cleaved horn-
blende. The prism-shape has been preserved, and some of the original crystals have conformed
to the plagioclases. In several of these phenocrysts a narrow hornblende rim is undivided
and has one and the same extinction, so that these phenocrysts may have represented horn-
blendes, which were intergrown with pyroxene in the core; this pyroxene must have been
altered into secondary hornblende. The granular groundmass consists of albite, hornblende,
biotite and quartz.

A similar rock has been abusively described as an uralite-diabase by J. H. Kloos (25)
on p. 59. This rock 120c, sampled by Martin near Shete, shows plagioclase and hornblende
phenocrysts in a groundmass of small plagioclase laths, hornblende prisms and needles,
allotriomorphic quartz and ore. Some of the hornblende phenocrysts are undivided, frayed
and contain small quartz-bubbles; many of them are prism-shaped hornblende aggregates
with small quartz-bubbles.

Hornblende-augite-quartz-vintlite (A267—D12266): The normally vintlitic ground-
mass contains many phenocrysts, which are plagioclases, hornblendes, a few pyroxenes

and a few quartzes. The plagioclase phenocrysts are andesine to labrador ; a single one must
be labrador-bytownite. The hornblende phenocrysts are partly or wholly altered. The
pyroxene phenocrysts are small diopsidic ones with a narrow rim of hornblende. The pyroxe-
nes and the groundmass in the close neighbourhood are rather strongly limonitized. The
quartz phenocrysts are round or rounded-off quartzes. Asingle one of them possesses arim
of small hornblende prisms, which are grouped more or less sheaf-like, and which stick in
the quartz substance with their free ends (reactionrim).

This vintlite, containing both pyroxene and quartz phenocrysts, has been found about
a kilometer S of Andicouri, in the diabase-schist formation, but not so very far from the
contact with the diorite batholith.

HORNBLENDE-PYROXENE-QUARTZ-VINTLITE, WITHOUT TRUE PLAGIOCLASE PHENOCRYSTS
(A 429—D 12514): The phenocrysts are hornblendes, secondary hornblendes (altered pj-ro-
xene) and quartzes. Plagioclase phenocrysts, if present, cannot be distinguished from the
groundmass plagioclases. The hornblende phenocrysts are for the smaller part normal, light-
green hornblendes. Most of them however are composed of secondary hornblende, which is
very probably pseudomorphic after pyroxene; this secondary hornblende occurs in idiomor-
phic or idiomorphic-rounded-off crystals, and is very Hghtgreen (at the very peripheric border
darker green) and diverse-fibrous. This secondary hornblende is partly chloritized. Where
this hornblende and the hornblendes of the groundmass border on each other, it is very
difficult to distinguish them from each other. In several of these pseudomorphic hornblendes
grains of titanite and magnetite occur, which probably have to do something with the
pyroxene alteration. Quartz phenocrysts occur many times as round or rounded-off crystals.
No reactionrims occur, but the hornblendes of the groundmass here and there conformed to
and around the quartzes; some of these hornblende needles even stick in the quartz substance.
The groundmass is normally vintlitic.

This vintlite containing altered-pyroxene and quartz phenocrysts occurs in the gabbro-
massive of the Matividiri, on the southern slope of this mountain.

Many of the quartz phenocrysts in the vinthtes possess remarkable reaction-
rims of hornblende (or pyroxene), whereas the quartz crystals of the porphyrites
do not show such rims. Moreover, the quartzes in the vintlites are strongly
rounded-off.

H. Rosenbusch (36) writes about vintlite quartzes on p. 560: „Wo Quarz *
„einsprenglingsartig sich noch findet, zeigt er die Form von gerundet^ Körnern,
„die sich oft durch Kränze von Amphibol oder Pyroxen als Fremdlinge aus-
„weisen . . G. J. H. Molengraaff (31) has found in some of the vintlite-rocks
of Curagao similar quartz crystals with hornblende-rims. He too considers these
crystals xenocrysts (enclosures), which do not belong to the vinthte magma and
have been taken up from elsewhere: (p. 45) „In navolging van H. Rosenbusch
„neem ik aan, dat deze kwartskristallen niet uit het magma afkomstig zijn. De
,,kwarts is door het magma opgenomen.quot;

However, the above-mentioned statements about the xenocrystic nature of
the big vintlite quartzes do not seem to hold good with regard to the quartz-
vinthtes of Aruba nor with regard to those of Curasao either.

The quartz phenocrysts of the quartz-diorite-porphyrites are idiomorphic
or have been more or less rounded-off and resorbed by magmatic resorption-
action. The quartzes of the quartz-vintlites are all rounded-off crystals or roundish

grains. - Many of the quartzes in the porphyrites contain fluid-inclusions, arranged
along planes. Also several quartzes of the vintlites contain such fluid-inclusions. -
Undulose extinction can be seen in part of the quartzes of both kinds of rock. - The
quartzes in both rocks are rather irregularly distributed in one and the same rock
and also in the different rocks. - The quartzes of the diorite-porphyrites are
sharply bordered on the groundmass or not, but do not possess reactionrims.
Many quartzes of the vintlites have well- or ill-developed reactionrims of horn-
blende (pyroxene, epidote, chlorite).

So, if we compare the quartzes in both kinds of rock, we see distinct similari-
ties and also differences; the vintlites have a lack of idiomorphic crystals, the
porphyrites have no crystals with reactionrims. On these differences Rosenbusch
and with him G. J. H. Molengraaff have founded their opinion that the vintlite
quartzes are xenocrysts. - However, why should only special vintlite magmas
take up exogenic quartz crystals, whereas other vintlites and diorite-porphyrites,
closely related to them and occurring in the same places, do not possess those
xenocrysts?! If we accept that the quartzes in the vintlites are of an exogenic
nature, we must also accept that, at least some of the quartzes of the diorite-
porphyrites are equally exogenic. However, if we accept - and this may be done
with reason - that the quartz-diorite magma produced dike-magmas of the com-
position of quartz-dioriteporphyrites andquartz-vintlites, and of dioriteporphyrites
and vintlites (without quartz developing into phenocrysts), there is no reason
why the quartz-vintlites could not have true quartz phenocrysts. - The lampro-
phyric dike-rocks, which have the same occurrence as the vintlites, and which
are also closely related to them, do not contain big quartz crystals (but for a
single exception). If the vintlite quartzes were xenocrysts, why should not the
lamprophyric rocks contain such xenocrysts too?!

Hence, we come to the conclusion that the big and undivided quartz crystals
of the vintlites are true phenocrysts as in the dioriteporphyrites. The reason
that they have been more resorbed than the porphyrite-quartzes and that many
of them possess reactionrims must be sought in the difference of magmatic action
in the more acid groundmass-liquid of the porphyrites and the less acid ground-
mass-liquid of the vintlites. Concerning the genesis of the reactionrim, see f.i.
F. Becke (4) and O. H. Erdmannsdorffer (18) i).

Many of the vintlite quartzes have well-developed reactionrims of horn-
blende-material, rarely of pyroxene, epidote or chlorite. Others are more or less
surrounded by the small hornblende crystals of the groundmass. Also quartzes
occur without rims (see also the strange quartz phenocryst in the transition-rock
A 265—D 12264, on p. 71). Moreover, it is very peculiar that hornblende pheno-

p. 273 (Relikte): quot;Wo ein Mineral an sich, noch im Bereiche seines Existenzfeldes
quot;liegt, aber in seiner Paragenese mit benachbarten Mineralien ein instabiles System darstellt,
quot;kann es gleichwohl als quot;instabiles Reliktquot; in die neue Paragenese hinübergerettet werden.
quot;Dies geschieht durch die Entwickelung eines Reaktionssaumes, der die quot;nichtkongressiblenquot;
quot;(d.h. in direkter Berührung nicht bestandfähigen) Phasen trennt, aber selbst mit dem um-
quot;schlossenen Relikt und den es umschliessenden Mineralien im Gleichgewicht steht (quot;Ge-
quot;panzerte Reliktequot; im Sinne von Esköla)quot;.

crysts of the hornblende-quartz-vinthtes D 12267 and D 12272. possess a rim of
small hornblende crystals of the groundmass (see p. 72).

As to the rounded-off quartzes of the hornblende-quartz-vinthtes D 12270,
D 12272 and D 12277,.jvhich consist of several small quartz individuals and which
in D 12270 and D 12272 have a kind of rim of small groundmass hornblendes
(see p. 72), we may better accept that these quartzes have been taken up as
xenocrysts (from the diorite! ?) and have been resorbed and corroded by the vint-
lite magma. At least, it seems difficult to recognize these composed quartz
individuals as phenocrystic elements.

The sample A 219, found near Alto Vista, is a dioriteporphyrite, which
contains a very big, rounded-off quartz fragment; it may be considered as an
exogenic inclusion, taken up from the country-rock (diorite!?).

The very long and large dikes can be seen in the geological map; many dikes,
however, have not been indicated.

As has been mentioned above, the bulk of the porphyritic rocks occur as
common dikes with nearly or quite parallel walls and with a length which is
considerably greater than the width. However, also dikes occur which have more
neck- or pipe-shape; the latter present themselves here and there as accumulations
of big blocks (monoliths; compare with the diorite), in consequence of selective
. weathering. - Here and there the contact between the diorite and the porphyritic
rocks is very clear; some dikes even enclose fragments of this plutonic rock

Some of the dikes in the older formation are clearly dioritic in the centre and
become more porphyritic in the ,,Salbandquot;. Such forms have not been found in
the diorites; they are due to the quickness of magma-cooling, which must have
been greater in the older rocks than in the batholith itself.

SE of Seroe di Poos di Noord a hornblende-quartz-vintlite dike ends against a
quartz-hornblende-dioriteporphyrite dike of 18m. wide; so here the dioritepor-
phyrite dike is probably the older one. N of Salinja Cerka a vintlite dike cutsquot;
through a granite dike and must be younger.

Some dikes have the length of about 1 km. or more, others have the length of
some hundred meters (see the map) and many are less than 100 m. to only a few
meters long. The width is also very different. The long dikes are rather wide.
Widths of 20—40 meters could be measured at dikes near, E and N of Alto Vista.
Many dikes have a width of about 10m. or more than 10m; such dikes especially
occur in the gabbro-massive of the Matividiri. Also many dikes have a width of
1—10 m, whereas only a few of them are less than Im. wide (the narrowest dike
which has been measured has a width of 3—4 dm.).

The dikes have different strikes, although strikes which do not differ so much
from the E—W direction prevail (see the map and diagram fig. 20). The bulk of
the dikes are vertical or almost vertical. Some of the dikes are less steep and
their dips could be measured; most of the dips lie between 45° and 90°, only a few

of them are less (f.i. 20°). - A few dikes in the hornblende-schists (metamorphic
tuffs) of the upper-course of Rooi Prins (near Juditi) he quite conformably in
these schists.

Some of the dikes have been faulted after their consolidation. F.i. the enormous
porphyrite dike, E of Alto Vista and N 150 E, has been cut through by a horn-
blende-dioriteporphyrite dike (N 70 E) and has been removed 10 meters south-
west-ward. The hornblende-vintlite dike, SE of Druif (N-Aruba. see map), has
been faulted in two places. Hence, not only the diorites but also the porphyrites
have been submitted to orogenic movements after their consolidation (compare
with the undulose quartz phenocrysts and other minerals).

It is a very remarkable fact that the bulk of the porphyrites and vintlites
occur in a zone along the N- (NE-) coast, 2—3 km. wide (see map). This zone is
bordered to the S and the SW about by a line which can be drawn from NW to
SE across Malmok-Salinj a Cerka - Turibana-Jaburibari-Zumbo-Seroe Pretoe
- Arikok - Juditi - Butucoe - Rincon. Still, dioriteporphyrites and vintlites have
been found in a small number S and SW of this line. Most of these dikes do even
occur not so very far from this line, that is to say, they occur in the NW—SE
central zone of the island and especially in the central part of this zone. It is
remarkable that porphyritic rocks are lacking in the large diorite outcrop N of
Savaneta, as far as is known. In the easternmost, large diorite outcrop only
two porphyritic rocks have been found, that is to say, a hornblende-diorite-
porphyrite 1,5 km. W of Boca Grandi and an ?epidotized porphyrite NW of
Seroe Grandi. The southern- and southwesternmost porphyritic rocks, as far
as is known, are a vintlite NE of Spaansch Lagoen. a dioriteporphyrite near Nanki
(near Seroe Colorado) and a quartz-dioriteporphyrite. transitional into vintlite.
on the Seroe Colorado (Martin 105).

Probably, this special distribution has something to do with the situation
in the batholith; the highest parts in the batholith probably contain the greatest
number of porphyritic dike-rocks, and these highest parts probably occur along

the N- and NE-coast and under the older rock mountains. - As far as can be seen,
there is a connection between the presence of pyroxene in the vinthtes and the
occurrence of these vintlites in the older diabasic series or in the gabbroic rocks of
the bathohth; the composition of the dike-magmas may have been a little altered
by addition of material out of the latter rocks.

This kind of rocks occurs as dikes, mainly in the bathohth and rarely in the
older rocks. They can be considered as differentiates of the dioritic magma,
which are younger than the porphyritic dike-rocks and which differ much more
from the diorite than these porphyritic rocks do. Yet, transitional rock-phases
have been found, that is to say, between the vinthtes and the malchites; some
malchites even have a somewhat dioritic character. Beside malchites, a few
spessartites and odinites have been found.

In the field these rocks can be clearly distinguished from the invaded batholi-
thic rocks, on account of the shape in which they occur and on account of their
colour and granularity. It is, however, rather difficult to detect them in the rocks
of the older formation.

Most of the malchites, described here, are normal malchites. Besides, there
will be described a malchite in contact with diorite, three aberrant malchite-rocks
(one of them in contact with diorite), a dioritic malchite, a biotite-malchite, a
pyroxene-malchite without quartz, a vintlitic pyroxene-malchite, and an epido-
tized and chloritized Pmalchite.

Normal Malchites (A 293—D 12302; A 295—D 12304; A296—D 12305; A 383—
D 12342; A 384—D 12343; A431—D 12516; A432—D 12517; A 433—D 12518; P 74-

D6169; P 75—D 6170; P 105—D 6179; P 105a—D 6179; P 71—D 6541): Macroscopically
they are aphanitic to finegrained, generally darkcoloured (black-grayish or dark-grayish;
rarely greenish). Bigger crystals of hornblende can be distinguished here and there. Small
diorite fragments occur enclosed in A 295 and A 296.

Microscopic description: The rock consists mainly of plagioclase, hornblende and quartz.
In most of the rocks the plagioclase takes up about as much room as or a little more room
than the hornblende; it must be mentioned, that in most of these rocks (an exception is
D 12343) much or rather much quartz occurs. In a few rocks (D 12304, D 12516, D 12517),
however, the hornblende takes up more room than the plagioclase; it is striking, that these
rocks contain only a little or very little quartz. A few plagioclase phenocrysts can be seen in
DD 6179. Hornblende phenocrysts in D 12304, scattered or in groups, are idiomorphic with
regard to the quot;groundmassquot; or not; some of them contain epidote and have partly been
altered into a fibrous chlorite. D 12342 contains several phenocrystic hornblendes and plagio-
clases. Flow-structures, particularly manifested by the small hornblende crystals, can be
seen in D 6541 and in D 12342. In some rocks the distribution of the hornblendes is not quite
a regular one, and in others the hornblendes occur in small groups here and there. In D 12517
a streak, composed of small fibrous hornblende prisms which lie roughly parallel, is very
curious.

Plagioclase: It is particularly striking, that in the rocks with much or rather much quartz
the plagioclases are not idiomorphic with regard to the quartz. On the other hand, the plagio-

clases of the rocks with only a little quartz (D 12304, D 12516, D 12343; labrador-bytownite
to oligoclase-andesine) are idiomorphic with regard to the quartz; these plagioclases are small
laths or short prismatic crystals. As to D 12517, its quartz only occurs in nests; its oligoclases
occur as very small grains between the numerous accumulated hornblende crystals. D 12305,
D 12342, DD 6179, D 6169, D 6170: the plagioclases are lath-shaped or prismatic bytownites
to labrador-bytownites; nevertheless they are not quite idiomorphic with regard to the
quartz; plagioclase-border and quartz work in with each other. Especially in D 12305 the
plagioclase-borders and the quartzes very intensively work in with each other, so that here
and there quot;dropsquot; of plagioclase seem to occur enclosed in the quartz, close to the plagioclase
crystals. Probably, the plagioclase began to crystallize; after that the quartz; these minerals
must have stopped their growth against each other at the same time; the final crystallization
must have had a more or less eutectic character. - D 12302, D6541: the plagioclases are
more isometric-granulose than lath-shaped labrador-bytownites, and work in with the
quartzes; D 12302 shows plagioclase quot;dropsquot; in the quartz. The albite-oligoclases in D 12518
are but here and there prismatic, and particularly occur in granophyric-micrographic inter-
growth with quartz. Only plagioclases in D 12304, D 12516 and D 12343 (rocks with a little
quartz!) are simply zonal. Most of the rocks contain many grains of epidote, zoisite and
titanite, scattered in and around the plagioclases.

The hornblende is on the whole the common green one; it is rarely brownish-green. In
D 12302 and D 12304 hornblendes occur with darkergreen and brown-green cores. The
hornblendes are prism-shaped, but do not show a good idiomorphism; they often have a
frayed habit (especially terminally frayed). The prisms are short or long and slender, even
needle-shaped. Concerning the relation between hornblende and plagioclase, they border
on each other in an irregular way. However, the small hornblende prisms in D 12305 are
rather idiomorphic with regard to the plagioclase, whereas on the contrary, many small
plagioclase laths in D 12304 are idiomorphic with regard to the hornblende (sub-ophitic).
As to the relation of hornblende to quartz, the crystallization of the two minerals in the
malchites with much or rather much quartz must have occurred, in general, at about the
same time (compare with the relation plagioclase-quartz and plagioclase-hornblende). In
D 12305 the hornblendes are rather idiomorphic with regard to both plagioclase and quartz.
In D 12516 and D 12343 (with a little quartz) both plagioclase and hornblende are idiomor-
phic with regard to the quartz. In D 12304 (with a little quartz), however, plagioclase is
idiomorphic with regard to both hornblende and quartz. Some hornblendes are fibrously
altered. Some of the hornblendes in D 12302 and D 6179—P 105 include small quartz-
bubbles.

Quartz: As to the occurrence of the quartz in the different malchites, see the relations
between plagioclase and quartz, and between hornblende and quartz. The quartz in D 12517
only occurs in roundish or eggshaped nests, not sharply bordered and consisting of granular
quartz or of quartz and plagioclase. There occur in D6541 some bigger, eggshaped quartz
crystals, surrounded by small hornblende crystals: exogenic inclusions?

Accessory minerals: Except in a few rocks apatite occurs as small needles. Magnetite can
be found as rare and diminutive grains; as a few grains, bigger and smaller ones; and as many
diminutive grains. Titanite occurs as small grains or crystals in many rocks. In D 6179—
P 105 many epidote grains and a few pyrite grains (with a limonite rim) occur along limonite
fissures.

A 751—D 13058 is a biotite-bearing malchite, occurring near Seroe Janchi. The bigger
hornblendes lie mostly in groups, between which the smaller ones are scattered. Biotite, of
minor importance, occurs as small greenbrown plates. The composition of the plagioclase is
about oligoclase-andesine.

The malchites described here occur by far the greatest part as dikes in the diorite batholith
(W of the diabase-schist-region). Some rocks occur as dikes in hooibergite-massives: P 105
and P 105a in the Hooiberg-massive, A 383 in the Turibana-massive and A 384 in the Seroe

km. W of Seroe dx Poos di Noord): The malchite-rock is sharply bordered on the d f^e'
There is no transition between the diorite and the malchite; on ^e other hand the Z o
clases of the dionte have a dead end against the malchite dike, and have partiy b;en re^^^^^^^^
by the malchite magma, so that these plagioclases are irregularly bordered on the dike Took
Smal apophyses of the malchite occur between the crystals of the diorite A very^ne low
structure is manifested by many small and lath-shaped phenocrysts that lie ZlneT Flor
structures in miniature occur around the diorite plagioclases, at the border of
ma chite is porphyritic; its groundmass takes up more room than the phenocrvsts
latter are plagioclases and hornblendes, both probably in the same quInritr-Tin fl J 5
The plagioclase phenocrysts are lath-shaped, here and there slightly zonal labralr
bytowmtes. The hornblende phenocrysts are long, lightgreen prisms. MlLvefth re^^^^^^^^^^
some bigger and more isometric plagioclases and hornblendes, that are quite idiomorphTc
f t; . -. ?'nbsp;resorption-holes. These crystals may be aLmilat^d crStIb

A zone of the groundmass along the border of the dike, about 1,5 mm broad is almost

dionte-contact. The groundmass of the quot;Salbandquot; looks grayish-brown and\lassv and
merges into the crystalline groundmass of the central parti ^he latter consists of a felt

An aberrant malchite (A 292-D 12301) has been sampled near Unia Unia in th.
diorite outcrop N of Savaneta. The main components are oliLlase ande^e iSrnblenL
and quartz,-the latter occurs but in a small amount. The small Lhs of plagTclksrare
morphic with regard to the quartz and are especially composed to sheaf^^^ike groups ^me^^
the pkgioclases are zonal. Brownish-green hornblendes, some of which with farke corror
with darker peripheric zones, are more or less idiomorphic prisms - a sineTe hornbtnH T quot;
a zonal extinction. Non-idiomorphic plates of chlorite^seem^: hlV^ ^nbsp;t o^^^^^^

but are of a minor importance. A little calcite must be secondary - Thi malch ^^
aberrant m the occurrence of the plagioclases and in the character o

m hornblende, and contains more hornblende than plagioclase. In connection h elvTtl it
quartz is very rare and occurs in nests. The plagioclase crystals, albites, albite o^a^^^^^^
occur as granular individuals between the many hornblendes. The hornb ende occ JHn tS
first place as small, brownish-green prisms, which are rather idiomorphic aS secondly S
bigger green and fibrous crystals, non-idiomorphic. Small hornblendele^;^^^^^^^^^^
hornblende), lying in sheaf-like bundles, radiate into veins of epidote. - TWs maTm^^^^
^berrant because of its richness in hornblende and because of the'special occurrequot;^

the beroe Pretoe. E of the Hooiberg; the latter rock forms a dike in hooibergite-rock Micro

scopically the crystals of the diorite and the malchite normally work in Jtrand be^X

each other, so that the intrusion must have taken place at a tinie when tlTe diorite waTnot

yet quite consohdated. - Quartz is only present in a very small amount and ratherTocaSy

The plagioclase is most important and occurs as grainy crystals of albite-oligoclase showing
a tendency to the lath-shape. The hornblende occurs: 1. as long and slender prisms, not
everywhere quite idiomorphic, and especially arranged in several star-shaped aggregates;
2. as some aggregates, composed of more isometric, non-idiomorphic crystals. Small brown
and green biotite plates and some chlorite are present here and there. Numberless diminutive
apatite needles and rods lie in the plagioclase. Some rather big grains of titanite are allo-
triomorphic with regard to plagioclase laths. Small cubes of magnetite. - This malchite is
mainly aberrant in the relation plagioclase-quartz, in the occurrence of the hornblende and
in the presence of biotite.

The dioritic malchite a 300—D 12309 has been found S of Kudawecha, and contains
an inclusion of quartz-hornblende-diorite. This malchite has partly a hypidiomorphic-
granulose texture, and consists of plagioclase, hornblende and quartz. The plagioclases,
labrador-bytownites to bytownites, show a lath-shaped development, and are partly idiomor-
phic with regard to the quartz; many plagioclases, however, work in with the quartz at
their borders; here and there very intensively, so that the plagioclase occurs as small quot;dropsquot;
in the quartz (no resorption-effects). The hornblende is the normal one-; some crystals possess
a periphery, which is darkergreen than the core. The crystals are non-idiomorphic and espe-
cially occur in groups. Some hornblendes contain quartz-bubbles. The quartz contains
fluid-inclusions in planes. Many small apatites can be seen, especially in the quartz. Titanite,
magnetite and a single pyrite crystal are accessory. - The dioritic character of this malchite
can be seen in the texture, in the rather great richness in quartz and in the occurrence of
fluid-inclusions in the quartz.

A 297—D 12306, W of the Hooiberg, is a biotite-malchite. It mainly consists of plagio-
clase, hornblende and biotite; quartz is of a minor importance; moreover, epidote is very
abundant as small grains. Flow-structures. Both plagioclase and hornblende have partly
developed as phenocrysts. The plagioclase phenocrysts have been almost wholly changed,
amongst others into a yellowish, almost isotropic substance, and are idiomorphic and prismat-
ic. The hornblende phenocrysts are small and short prisms. The small plagioclases are laths
and prisms, especially zonal oligoclase-andesines to andesines. Small prism-shaped horn-
blendes are only a little different from the phenocrysts. Very small and brown biotite plates
occur as separate crystals or in strings; part of the hornblendes join these strings. Probably,
the biotite material takes up more room than the hornblende material. It is not probable
that the biotite is secondary.

A pyroxene-malchite, without quartz (A 299—D 12308), N of the Jaburibari,
consists of hornblende (the most important mineral), plagioclase, and pyroxene (a little).
The plagioclase crystals occur more or less as laths between the hornblendes (sub-ophitic
texture). They are slightly zonal labrador-bytownites; a single one even shows recurrence.
The hornblendes are bigger or smaller crystals. The latter are, firstly, brown-green with a
green rim (some of which even possess a zonal extinction) and with a rather good idiomor-
phism; secondly, lightgreen, more fibrous (secondary hornblende ?!); both kinds of hornblende
merge (!). The bigger crystals, which are no true phenocrysts, are non-idiomorphic, very
lightgreen; some of them contain a diopsidic augite in their core. Part of the lightgreen
hornblendes may be uralite after pyroxene.

N of Alto Vista a dike-rock has been found, which probably represents one of the transition-
al rocks between the vintlites and the malchites: vintlitic pyroxene-malchite (A 298—
D 12307). The groundmass takes up more room than the phenocrysts; the latter mainly are
hornblendes, less altered-Pplagioclases and a few pyroxenes (in groups). PPlagioclase pheno-
crysts have quite changed into epidote, with preservation of the original, non-idiomorphic
shape. The hornblende phenocrysts are idiomorphic or rounded-off. Some of them are fibrous.
A single one contains pyroxene in its core (partly uralitized pyroxene?). The pyroxene pheno-
crysts are non-idiomorphic diopsidic augites. Groundmass: A felt-like mass of small hornblende
prisms, needles and fibres, with lath-shaped oligoclase-andesines to andesines and quartz.
Here and there more or less eggshaped quartz nests can be found, not sharply bordered ont
the groundmass.

Sample: Normal quartz-hornblende-(biotite-)diorite with a dike of a. o
darkgrayish rock, in which greenish-weathered phenocrysts can £ ten The'h .
between diorite and odinite is not quite straight but shLp

Microscopic description: The odinite dike-rock is sharply bordered on the diorite;
plagioclase and hornblende crystals of the diorite have been cut off and partly somewhat
resorbed by the intruding odinite magma. Small apophyses of the dike occur between the
crystals of the diorite. - The rock is porphyritic; its groundmass takes up more room than
the phenocrysts. The latter are pyroxenes, and lie closer together in the quot;Salbandquot; than they
do in the central parts.

The pyroxene phenocrysts are colourless diopsidic augites, idiomorphic or rounded-off,
partly resorbed and fragmentary. A very few are twinned. Masses of a yellowish uralitic
mineral and of a yellowish chlorite are pseudomorphic after pyroxene or plagioclase pheno-
crysts.

Groundmass: The quot;Salbandquot;, about 1—1,5 mm. wide, is almost aphanitic, brownish-
coloured and glassy, and merges into the groundmass of the central parts of the dike; the
latter is composed of a felt-like mass of small hornblende needles, with some Pplagioclase,
Pquartz, Pchlorite and Pglass. In the felty groundmass numerous very small ore grains can
be seen, part of which are limonitized. In the groundmass of the quot;Salbandquot; some bigger
magnetite grains occur; moreover many diminutive, green-grayish spots, which may be
ore-remnants (Pleucoxene).

It can be mentioned that the original composition of the lamprophyre-plagioclases is
more basic than that of the plagioclase phenocrysts of the diorite-porphyrites. The difference
in composition, however, between these minerals in lamprophyres and vintlites is very small,
whereas the basic augite-vintlites have plagioclase phenocrysts which have about the same
composition as the plagioclase of the lamprophyres.

The lamprophyric dike-rocks, in general, do not occur in such large dikes as
the porphyritic ones and have, therefore, not been indicated in the geological map.
They present themselves in normal dikes, not in pipes. Here and there they crop
out as round blocks (monoliths) in consequence of the selective weathering, f.i.
N and E of Alto Vista and on the Jaburibari (reddish-brown blocks). Near Alto
Vista and on the Urataka complexes of lamprophyric dikes occur. Several dikes
contain fragments of the diorite. No ,,Salbandquot;-textures could be distinguished
in the field, only under the microscope.

The relation in age between the lamprophyres and the dike-granites and
porphyritic rocks can be studied f.i. in Rooi Santoe just N of Salinja Cerka, where
a malchite-dike cuts through a granite- and a vinthte-dike; it is clear that the
malchite must be of a younger age than the two other rocks.

As has been said, the dikes are generally of a small length and width. The
length is mostly but a few meters; the width is in general no more than 1 meter.
Yet, there have been found some d kes with a width varying from a few meters
to 10 meters, especially in the northern parts of the batholith.

Varying strikes have been found (see diagram fig. 21, p. 78). Most of the
dips are vertical or almost vertical; a few dikes are less steep, dips of about 60°
and 25° having been found. — N of Jaburibari a dike runs N 150 E; its western
part has been removed a few meters to the north, with regard to the eastern
part (orogenic movements). lt;

along the north(-east)-coast, 2—3 km. wide, and the other part of the batholith
as m the porphyritic rocks (see there). The lamprophyres are widespread in the
whole northern and western outcrop of the batholith; still, it is remarkable, that
m this outcrop the number of dikes increases from SW to NE (respectively
from the deeper to the higher parts of the batholith), so that in general the same
order holds good with regard to both porphyritic and lamprophyric dikes -Only
one rock has been found in the batholith outcrop N of Savaneta (near Unj a Unja)
whereas in the easternmost outcrop not one could be observed. - Some dikes run
through the contactzone between gabbro and diorite, near Bushiribana, Matividiri
and Sumpina, and must have intruded after the contactprocesses had finished
A single dike occurs in the gabbro-massive. - As has been mentioned above, the
lamprophyres are almost wanting in the older rocks. Only one dike (N 135 E) has
been found in the southern mountains, S of Seroe Blanco; it cuts unconformably
through the hornblende-schists. The poorness in lamprophyric dikes here may be
understood if we take into consideration that the dikes are generally very small
and narrow; the amount of lamprophyric magma must have been too small for
It to break through the batholith-roof, but for a single exception. The difficulty
however, to distinguish lamprophyric dike-rocks from the diabases and meta-
morphic tuffs is certainly one of the causes that lamprophyres have hardly been
observed. The poorness in lamprophyres in the older rocks must be very probably
ascribed to both these influences.

These dike-rocks are very probably the youngest differentiates in the batho-
hth. They belong partly to the magmatic period of crystallization (dioritic aplites
granodioritic aplites, granitic aplites, gabbro-aplites, quartz-albitites, granitic
pegmatites), partly to the epimagmatic period (pegmatites, quartz-rocks, quartz-
epidote-rocks, epidote-quartz-rocks, epidote-rocks; metalliferous quartz-rocks)-
the rocks of the latter group must be of an aqueo-igneous or of hydrothermal
origin.

They form dikes and veins in the batholithic rocks and also in the diabase-
schist formation, as well as in the contactzone of the latter.

The dikes can be clearly distinguished from the invaded rocks because of
their shape and colour, the latter being a very light one. The dikes, in general, do
not appear as elevations in the landscape.

Macroscopically these rocks are mostly mediumgrained; they consist mainly of feld-
spar and quartz; the dark mineral is hornblende, which occurs as a few and small crystals

Microscopic description: The texture is mainly pan-allotriomorphic-granulose (aplitic).
In these rocks quartz and plagioclase are, quantitatively, about equivalent D 12317 is more
dioritic in the central parts of the dike, more hornblende crystals being present here

Some of the plagioclase crystals show a remarkable tendency to idiomorphism (with
regard to quartz; seldom with regard to hornblende, f.i. in D 6561). The composition is
rarely oligoclase, mostly oligoclase-andesine. In D 12329 there is a clear connection between
the strong albitization and the polysynthetic twinning (see fig. 22).

Quartz: It is a remarkable fact, that the quartz individuals in D 12329 are stretched
about parallel to the dike-borders, and that the undulose extinction and the lines of fluid-
inclusions show a certain parallellism to the dike-borders as well.

The hornblendes are here and there idiomorphic with regard to quartz and plagioclase.
So, the sequence of crystallization is not entirely wanting; a consolidation-residuum may
even have attacked former more idiomorphic hornblende crystals.

Accessory minerals are apatite, magnetite, titanite, zircon (D 12329; a single crystal in
hornblende), Psillimanite (D 6561; small needles). — D 6561 contains a mass of chlorite with
epidote and titanite strings.

Dioritic Aputes (Hornblende-diorite-aplites) : A 80—D 12048; A 81—D 12049.
(dikes in diorite). Some rocksamples consist of both the quartz-hornblende-diorite and the
dioritic aplite dike. Hence, the transition and the difference between the plutonic rock and the
dike-rock could be studied. The difference is very clear on account of the smaller quantity
of the hornblende in the aplite; in connection herewith the quantity of quartz is greater. The
crystals of both rocks work in with and between each other, and a true quot;Salbandquot; is wanting.
According to this transition, and also to the more or less plutonic texture of the dike-rock
we can assume that the dike-intrusion took place during the last stages of the diorite consoli-
dation. Thus, an interchange of material may have occurred.

In sample A 80 the hornblendes lie about parallel to the border of the dike, indicating
a flow-structure. The texture is mainly hypidiomorphic-granulose. perhaps partly pan-
allotriomorphic-granulose. There may be more quartz than feldspar, or the other way about,
possibly depending on the degree of interchange with the dioritic rock.

Plagioclase is sometimes idiomorphic with regard to the quartz. Sometimes it is hypidio-
morphic or allotriomorphic, which may be caused by a resorption-action by the late stage
quartz-fluid or by simultaneous crystallization with the quartz. In D 12049 the crystals are
the less dusty the farther away they occur from the diorite. In general, they are the same as
the plagioclases of the diorite and have a composition of oligoclase to oligoclase-andesine.

Quartz is in general the youngest constituent part. In D 12049 the quartz amount
increases from the dike-border to the centre. Hornblende is here and there idiomorphic.
Apatite, magnetite and titanite; zircon seems to occur in D 12049.

Granodioritic Aplites (Biotite-granodiorxte-aplites) : A 82—D 12050; A 83—D
12051; A 84—D 12052; A 168—D 12239.

These aplites contain no hornblende but biotite as dark mineral. They are mainly

finegrained rocks with gray, yellow or orange-brown quartzes, white feldspars and few
black biotites. The texture is pan-allotriomorphic-granulose. Generally, plagioclase consti
tutes the majority with regard to the potashfeldspar. Biotite is of a minor importance

Some of the plagioclase crystals are partly idiomorphic with regard to the other minerals
Oligoclase to oligoclase-andesine. D 12050 shows myrmekitic intergrowths bordering on
potashfeldspar. In D 12052 (granophyric granodiorite-aplite) a great part of the plagioclase
IS in granophyric intergrowth with quartz, partly with radial appearance. Very clearly there
can be seen the transition of plagioclase and quartz into the granophyric intergrowth while
even the twinning partly is present in the granophyric plagioclase. - Potashfeldspar is
present as dusty orthoclase, microcline, microcline-microperthite and microperthite
In D 12051 the quartz partly occurs in cataclastic zones between the feldspars In D 12050
a single quartz is idiomorphic.

Biotite is present as scattered plates. Especially D 12050 contains socalled quot;streaksquot;
of small biotite crystals, that have probably drifted together. In this case it is evident that
the biotite crystallized before the other minerals. In the same rock small muscovite plates
have been found, chiefly in the neighbourhood of the biotite groups. Whether the muscovite
is wholly or partly secondary or primary remains uncertain. Also in D 12239 muscovite is
met with.

Magnetite, apatite and titanite are accessory. In D 12052 and D 12239 very small rods
scattered through the rock, may be sillimanite needles. D 12239 possesses a biotite with an
enclosed Pprimary epidote.

Granitic Aplites. (biotite-granite-aplites) : A 85—D 12053; A 86—D 12054- A 87—
D 12055; A 88-D 12056; A 89-D 12057; A 90-D 12058; A 91-D 12059; A 92-D 12060quot;
A93—D 12061; A 360—D 12338; A 361—D 12339; P 72—D 6542.

They look like the granodioritic aplites. The texture is normally aplitic, and the crystal«
are especially equigranular. The main constituent minerals are potashfeldspar, quartz and
plagioclase; biotite and muscovite are of a minor importance. Part of the rocks look very
cataclastic: narrow zones of fine-cataclastic quartz occur between the feldspar crystals
especially between the potashfeldspars; the quartz grains work in with them

Four kinds of potashfeldspar. that is to say orthoclase. microperthite. microcline and
microclme-microperthite. occur in different quantities. D 12060 shows an irregular inter-
powth of potashfeldspar and quartz. InD 12053 some of the potashfeldspars show a poikilitic
habit, enclosing idiomorphic quartz and plagioclase crystals. The potashfeldspar is verv
dusty; in D 12056 dust-lines occur along the layers of albite in the perthitic potashfeldspars
In some of the crystals of D 12059 irregularly shaped and narrow zones of albite probably
represent no perthitic layers but lines of albitization (phase of youngest alteration)

Plagioclase generally occurs in a smaller amount than potashfeldspar. In many rocks
plagioclases occur with a simply zonal structure, that is to say. in far the most cases with a
core and one more acid zone. Core and zone are distinctly separated or pass gradually into
each other^In the former cases the zone may be quot;resorptivequot; with regard to the core- by
way of exception more zones may occur, partly being recurrence-zones. The average compo-
sition is oligoclase, hence more acid than in the granodioritic aplites; some crystals have an
° ™nbsp;'''' albite-oligoclase zone. The plagioclases of D 12338 are albites; those

of D 12339 oligoclase-andesines. Most of the plagioclases are allotriomorphic; nevertheless
some crystals show a tendency towards idiomorphism (with regard to the quartz and the
potashfeldspar). In D 12053 and D 12060 many myrmekitic intergrowths of plagioclase and
quartz border on potashfeldspar; especially in D 12060 many of them have a feather-shape
(fig. 23). In the latter rock myrmekites with core and zone occur (zonal plagioclase) Most
of the plagioclases in D 12061 occur in very fine, radial, granophyric intergrowths with quartz
(granophyric granitic aplite); these plagioclases are in general not lamelled. There are transi-
tions of quartz and of twinned plagioclase into such granophyric intergrowths

Quartz: A few quartzes show a tendency towards idiomorphism or are idiomorphic with
regard to the potashfeldspar.nbsp;.

Small biotite plates occur as independent crystals, or in streaks and aggregates. Many
epidote grains can be seen in the close neighbourhood of the biotites. Frequently also very
few and small muscovite plates are present, less than biotite. It is difficult in some cases to
distinguish them from the secondary sericite in the feldspar.

Magnetite is rare or is present in a small amount. Part of the grains have a rim of epidote.
In other aplites a great part of the ore is tied to the biotite. In D 12057 the ore occurs in
curious groups of grains and of crystals, between and around which epidote-like and chlorite-
like substances can be seen. - A few apatites. - In D 12059 and D 12339 rare titanite occurs
next to magnetite or biotite: primary or secondary? - Zircon seems to occur in D 12053 and
D 12058. - In D 12053, D 12055(?), D 12057, D 12061 and D 12339 small needles and prisms,
for a part brownish, may be sillimanite. - D 12054, D 12056, D 12060 and D 12338 may
contain primary epidote as idiomorphic crystals, wholly or partly enclosed in biotite.

These granitic aplites occur as dikes in the diorite batholith or in hooibergite-rocks i).

Gabbro-Aplite (A 100—D 12067): Only one sample of this rock-type has been found,
SE of Canashito. It is a finegrained, grayish, siliceous-looking, aplitic rock, in which small
black spots can be seen: the dark minerals.

Microscopic description: The texture is allotriomorphic-granulose, although many
plagioclases show, it is true an irregularly bordered, lath-shape. The rock mainly consists of
quartz and plagioclase, less of hornblende and mica. Locally, there are granophyric inter-
growths of quartz and plagioclase. The occurrence of small plagioclase quot;dropsquot; included in
the quartz, just outside of the plagioclase crystals (see plate III fig. 6), is very common; the
extinction of all these plagioclase inclusions is the same as that of the big plagioclase crystal
to which they apparently belong. Probably, the plagioclase began to crystallize before the
quartz. The remaining quartz-plagioclase-liquid crystallized afterwards more or less grano-
phyrically, possibly after having partly resorbed the already formed plagioclases. The new-
crystallized plagioclase got the same crystallographic orientation as that of the neighbouring
and older crystals. - Plagioclases locally lie in groups between the quartz individuals: labrador
bytownites. - The quartz contains rare fluid-inclusions.

Hornblende occurs a little more than biotite, and partly as separate, more or less
skeleton-shaped crystals, that may owe their shape to resorption-effects. The hornblende,
however, is chiefly present in groups of small, non-idiomorphic crystals, together with biotites,
magnetites and apatites. A great number of quartz-bubbles occur in the hornblendes. Moreover
resorption-holes in some hornblende crystals due to the reaction-effects of the quartz-liquid
(compare with the relation between plagioclase and quartz) are present; a connection between
the occurrence of the many quartz-bubbles and the resorption-action of the quartz-fluid
seems to be obvious in this rock (see also p. 96). - Biotite plates are scattered through the
rock, or occur near and between the hornblendes. Muscovite is present as a few small plates.
- Many apatites occur together with magnetite and titanite near and between the dark
minerals. The amount of magnetite is rather big; a single grain of pyrite is present. Titanite
is especially to be found around the magnetite, and may be of a secondary genesis. - In the
neighbourhood of the dark minerals large masses of epidote occur.

A 94—D 12062; A 95—D 12063; A 96—D 12064; A 97—D 12065; A 182—D 12507;
A 745—D 13053.

The rocks are fine- to mediumgrained, and have an aplitic texture. The plagioclases,

J. H. Kloos (25) p. 43 called a similar rock (93*) microcline-granite and saw in the
sample quot;kleine hellrothe Granatequot; (?). According to him, the bending and the flexion of the
twinlamels quot;lassen sich leicht erklären durch den Druck, den der nachträglich auskrystallisi-
quot;rende Quarz bei seiner Festwerdung auf die bereits vorhandenen Mineralien ausübte und
quot;ist es unwahrscheinlich, dass hierbei andere mechanische Vorgänge mitgewirkt haben
quot;sollten.quot; - The quartz itself shows effects of stress as well. In comparison with the other
rocks of the batholith and with the general orogenic relations the conclusion seems to be
more reasonable that the distortion-phenomena in the feldspars and quartzes are due to
slight orogenic movements during and after the magma-consolidation.

mostly albites, can be idiomorphic with regard to quartz, allotriomorphic with regard to
Idiomorphic quartz, or these two minerals can occur in micrographic-granophyric intergrowth
The rocks show clear effects of stress; amongst others, fine-cataclastic quartz zones between
the bigger minerals, and quot;Schachbrettquot; albites. A few biotite plates, chloritized or not
especially occur in streaks. Chlorite may also be newly added, f.i. in the quartz zones oi
u 1Z507. D 13053 contams several fibrous muscovites with leucoxenic flocks. The epidote
partly lies in strings through the rock. Apatites, magnetites, titanites and rare zircons are
accessory. Moreover, D 12065 contains very small, partly brownish, needles and prisms, which
may be silhmanites. A single epidote here is pleochroitic from grayish-brown to colourless
and has the interference-colour of zoisite; a few others are idiomorphic. In D 12063 apatite
needles are very abundant in the quartz, and occur less in the plagioclase. The presence of
many zoisite prisms, which occur only in the quartz, is very curious; here and there these
prisms are arranged to sheaf-like aggregates. According to Weinschenk (51) p. 151 and p 152
these zoisite crystals may be primary a-zoisite.

^ which shows affinities to the quartz-albitites is A 746-D 13054, found about
1 km. W of the Hooiberg. It is a parallel-structured, white-grayish aplitic rock which

under the microscope shows a clear parallel structure as well. It consists of layers of finer and

coarser grained, undulose or strongly cataclastic quartz. Several broken or bent albites lie in
these layers, and the quartz zones curve around them. Some layers are very rich in epidote-
the latter mmeral also occurs in masses, with here and there a little fibrous chlorite - It is
c ear that this rock must have been submitted to a great pressure, which caused the parallel
structure. May be, the original rock had the composition of a quartz-albitite.

teJdspar the latter takes up more room than the quartz. The quartz is white. The feldspar
has a white or „beige colour, and its crystals, orthoclase and albite, are very dusty
mi.nbsp;^^^f® ^ coarsegrained feldspar-quartz-rock, principally composed of big

m croclme crystals with a beautiful cross-hatching. The intergrowth of the feldspar and the
quartz is not a graphic one, but an irregularly granophyric one. The irregularly shaped
rnprf'nbsp;the microcline cause a rather curious appearance of this feldspar. The spotted

irregular way. Between those bigger crystals quot;nestsquot; of smaller ones occur here and there.
The quartz is very dusty. Its gas- or fluid-inclusions occur in a kind of network.

The rock A 101_D 12068 (belonging to the very long dike N of Spaansch Lagoen) is a
siliceous one with beautiful, reddishbrown and bright-green colours, alternately. It is a quartz

altered into limonite. A little ore. reddishbrown in reflected light and possibly cuprite is

zone farthest from the dionte consists only of quartz. Narrow quot;veinsquot; or zones of very smaH

quartz grains occur between and through rather big individuals, which show but here Id

there idiomorphism. The quartz is filled allover with fluid-inclusions, partly Lran^ed quot;n

planes. The second zone consists of an aggregate of finer grained quartz and a little chlorite,
in which bigger, more or less idiomorphic or fragmentary quartzes and some sericitized,
lamelled albites lie. The third zone nearest the diorite consists of big quartzes, here and there
idiomorphic, between which finer grained quartz occurs, and moreover of sericitized albites
and masses of chlorite. Ore is present in a few semi-limonitized magnetite grains. - The
albites and the chlorite must be altered diorite minerals, between which the quartz-liquid
must have penetrated and which must have been taken up in the quartz-dike. The albitiza-
tion and chloritization of the plagioclases and hornblendes are very probably due to the same
quartz-liquid injection and flooding.

Quartz-epidote-, epidote-quartz- and epidote-dike- and vein-rocks (A 72—
DD 12039, 12040; A98—D 12066; A 102—D 12069; A 103—D 12070; A 104—D 12071;
A 105—D 12072; A 106—D 12073; A 107—D 12074; A 109—D 12076; A 110—D 12077;
A 111—D 12078): Macroscopically these rocks are greenish, greenish-gray, yellow-greenish-
gray or brownish, more or less siliceous-looking ones, in some of which narrow quartz veins
clearly can be seen.

The rocks consist of varying quantities of quartz and epidote, irregularly distributed in
most of them. Where the epidotes are prisms or columns, they sometimes lie in a radial way.
In one place of D 12071 filiform microlites diverge from the epidote aggregate into one of
the quartzes. In D 12069, D 12071 and D 12073 both minerals occur in a banded structure.
Some chlorite here and there occurs between the epidotes; rarely sericite (D 12077). -Several
other minerals can be found which probably have been taken up from the country-rock:
distorted albites in D 12069; remnants of biotite, transformed into chlorite and titanite or
not, in D 12073 and D 12076; magnetites, apatites, titanites.

A 72 is a quartz-biotite-diorite with a fissure, in which green, filiform or needle-shaped
crystals clearly can be seen. In the DD the epidote-quartz-vein is bounded by the diorite in
a rather sharp wa}*-, except in the places where the quartzes of the two rocks touch each other
and seem to have fused.

D 12066 is a granite-pegmatite with a nest of epidote. Between the epidote individuals
some quartzes occur, which enclose irregularly shaped pieces of potashfeldspar. Epidote
crystals stick in the microcline of the pegmatite.

Quartz-talc-epidote dike-rock (A 434—D 12519): This rock is a dirty-grayish-
green-, brownish- and blackish-looking, schisty rock. It is composed of a finegrained
quartz aggregate, with epidote and talc, irregularly distributed. The epidote is
grainy, and here and there arranged in strings. The talc is present as stretched scales and
plates. Moreover there occur several enclosed plagioclase crystals, roundish and strongly-
pressed, and a few limonitic grains of magnetite.

It is a dike-rock in diorite of the Hooiberg. Both talc and epidote may have originated
from the Ca- and Al-bearing ferromagnesian minerals of the hooibergite. The enclosed
plagioclases may have been taken up from the hooibergite or from the diorite. - The dike
strikes N 30 E and dips 45 NW.

Chlorite-epidote-rock: The rock A 753—D 13060 probably occurs as a dike in the
diorite S of Kudawecha and can be described in addition to the epidote-dike-rocks. It is a
greenish rock with lustrous, greenish-black plates. The main mineral is slightly pleochroitic,
lightgreen, platy or radial-fibrous chlorite, undulose or broken (angle between the optic
axes 0°; optically positive; main zone negative; velvet-like, greenish-gray interference-col-
ours). Brownish, leucoxenic spots lie parallel or radial in these big chlorites, between which
a kind of groundmass of small epidote prisms and similar chlorite occurs. Moreover, some
quartz, a little calcite and brownish Pleucoxene are present.

The leucocratic rocktypes cannot be rigorously separated from each
other. Transition-rocks prove that they are differentiates of one and the same
magma, in so far as they are true magmatic rocktypes.

The aplitic and albititic rocks are normal, leucocratic differentiates of a
dioritic magma and are of an igneous nature. As to the pegmatitic and quartzose
rocks we probably cannot consider them differentiates of a merely igneous nature
They belong to the epimagmatic period of consohdation of the batholithic ma'-mas
According to J. E. Spurr (43) p. 70 we can call the pegmatite, quartz and
metalhferous quartz dikes and veins „veindikesquot;, the magma of these rocks
being intrusive, but differing from that typical of the usual igneous rocks- the
magma approaches the solutions from which veins are deposited, and represents
an extreme differentiate (an aqueo-igneous end-stage consolidation product) i)
The most important metal in the quartzose veindikes is free gold; most of these
auriferous quartz-rocks occur in tabular vein form, some of them in more lens-
shaped forms. According to Spurr (43) p. 85 these veindikes must not have been
formed at a great depth. According to W. Lindgren (28, pp 546—549) the
goldbearing quartz-dikes belong probably to the group „Metalliferous deposits
at intermediate depths by ascending thermal waters and in genetic connection
with intrusive rocks.quot; Here and there also a little pyrite, chalcopyrite and malachite
have been found. - It is questionable whether the quartz-epidote-, epidote-
quartz- and epidote-dikes and -veins are also,,veindikesquot; or are more hydrothermal
veins. Probably, there is a transition, so that the epidote-rocks rich in quartz
origmated from a liquid thinner and more aqueous than the true veindike magmas
whereas the epidote-rocks poor in quartz or without quartz are hydrothermal'
In addition herewith it must be mentioned, that most of the batholithic rocks
contain very narrow and small veins of epidote or of epidote and quartz, obviously
of hydrothermal origin and impregnated along fractures and fissures. These rocks
have been generally epidotized in the neighbourhood of these veins. The solutions
of the biper epidote- and epidote-quartz-dikes too attacked the country-rocks
whether belonging to the older formation or to the batholith. This can be clearlv
seen f.i. in the rock A 747-D 13055, which presents a dioritic rock gradually
merging into a quartz-dike-rock (p. 83).nbsp;0 .y

The leucocratic rocks, being widespread and occurring generally in dikes of
small dimensions, have not been indicated in the geological map

On the whole, they present themselves in normal dikes and veins; rarely
in pipe-shaped dikes, which have been preserved here and there by selective
erosion and which occur in the landscape as small tops and hills. Locally, a dike-

differentiates of a more basic magma. On the other hand, Ehdmannsoörfker (18) p. 225

and Bowen (7) p. 131 believe the (metalliferous) quartz-veins to be formed f om higljy
aqueous residuums, hence under hydrothermal conditions. According to Bowen Suc^
„hquids are m no sense magmas as the term is ordinarily used, for this usage implies a
^ TTnbsp;^nbsp;-th subsequent congelaTon is

or a pipe-shape cannot be distinguished, the leucocratic rock occurring as a small
massive in the diorite (f. i. an aplite massive just E of Zumbo). The aplitic dikes
rarely crop out as big, roundish blocks hke the diorite. ,,Salbandquot;-textures could
not be found.

The leucocratic dike-rocks are very probably the youngest in the bathohth.
They mainly occur in the diorite. In a few places they cross diorite-dikes. North of
Du Chef quartz-dikes seem to branch out from a porphyrite-dike.

The bulk of the dikes and veins have small dimensions. Yet, some very
long dikes have been found; f. i. a leucocratic dike of more than 200 meters long
in the gabbro-massive of the Matividiri, an 80 meters long granite-aplite dike
NNW of Arikok in the diabase near the contact with diorite, a leucocratic dike
more than 200 meters long S of Santa Cruz, a quartz-dike of about 1400 meters
long in the diorite N of Spaansch Lagoen; on the Arikok also a rather long quartz-
dike occurs. — The width is generally small, and varies from a few cm. to about
3 meters; the long dikes are rather wide (aplitic and quartz-dikes). The long
quartz-dike N of Spaansch Lagoen wedges out to the east. Thegabbro-aplitedike
SE of Canashito, is more than 5 meters wide; and a granite-aplite outcrop 800
m..E of Seroe Blanco (SE-Aruba) has a length of about 100 meters and a width of
about 40 meters (E-W stretched).

Varying strikes have been found (see diagram, fig. 24). Most of the dips are
vertical or almost vertical; some dikes are less steep, the dips lying for the greater
part between 45° and 90°; a single dike is about horizontal. —• Some dikes in the
southern part of the older formation lie conformably in the schists there; a dike
in the contactzone of NW-Aruba too shows the same strike as the amphibohtes. —
A dike near Druif (NW-Aruba) has been faulted once (orogenic movements).

The leucocratic dike-rocks are widespread in the batholith. It can be men-
tioned that the number of dikes found^ in the batholith is much greater than that
in the older formation; whereas the latter seem to be almost wanting in the

eastern parts (region of Dos Playa, Fontein, lower course of Rooi Prins), that is to
say, in those parts of the older formation which lie far from the batholith. In
distinction to the distribution of the porphyritic and lamprophyric rocks the
leucocratic dike-rocks are regularly distributed and their number does not in-
crease from SW to NE. The easternmost batholith outcrop contains several dikes,
but the outcrop N of Savaneta contains only very few. Numerous dikes and
veins especially occur in the contactzones between diorite and the older formation
and between diorite and hooibergite-rocks or gabbros.

The resorption phenomenon described on p. 40 where a more acid shell of
plagioclase shows a resorptive character with respect to the more basic core, can
be compared with the relation between the hypersthene and hornblende of the
gabbroic rocks. In both cases the remaining liquid must have reacted with and
must have partly resorbed the already crystallized substances during a phase
of slow cooling. These plagioclases do not form a true continuous reaction series
but can also be considered as a kind of discontinuous reaction series. The more
acid plagioclase shell has crystallized during a phase of rapid cooling, either from
a residual liquid originated on the spot, or from a residual liquid newly added.
In the latter case, there must have been a relative motion of liquid and crystals.
According to Bowen (7, p. 276) the total composition of this liquid is changed but
little by the partial solution of the older crystals. — Although the genesis of the
hornblende shell and that of the acid plagioclase shell in the hypersthene-gabbros
have the same character, the hornblende must have been formed in an earlier
period than this plagioclase and at about the same time as the more basic
plagioclase.

As to these resorption phenomena also O. H. Erdmannsdörffer (18, pp.
238—239) gives as his opinion that the resorption took place during the normal
course of magma consolidation in consequence of the faihng of equilibrium
between the already crystallized minerals and the remaining liquid. Besides
however, he remarks that resorption can be caused by ,,äussere Eingriffequot; as well:
,,Auch Wärmezufuhr, Druck- oder Konzentrationswechsel, z.B. durch Extrusion
,,oder plötzliche Entgasung, kann zu Gleichgewichtsverschiebungen mit ähn-
„lichen Ergebnissen (resorption) führen, ebenso Aufhebung von Uebersättigung
„und Ähnliches. Beispiele liefern die stark verrundeten Quarzdihexaeder in
„liparitischen Gesteinen, die zerfressenen Formen der früh ausgeschiedenen Kerne
„zonargeschichteter Mischkristalle, z.B. Plagioklase in dioritischen Gesteinen.quot;—
In order to understand the hmitation of the resorption of the older cores, see
Bowen (7, pp. 275—276).

Since the recognition of this plagioclase resorption phenomenon greatly depends
on the situation of the section it is very difficult to form an idea of its quantitative
occurrence. Possibly all the plagioclases show the phenomenon, partly
beside their normal zonal character; the latter must have come into exist-
ence in an earlier period during a rather quick cooling. Such a general occurrence

could be very well understood. On the other hand, it is also possible that only
locally in the batholith this resorption took place.

Considering now the later resorption of plagioclase and hornblende by a
SiOa-rich liquid, resulting in the occurrence of quartz in peripheric holes of these
older minerals, such a resorption must be due to the action of the end-stage
residual hquid, very rich in SiOa, alkali and volatiles, and with a great corrosive
power. In part and beside quartz also potashfeldspar must have crystallized from
this liquid, as found in some of the dioritic rocks. The residual liquid may be
newly added instead of a differentiation from the spot. Probably it had about the
properties of an eutectic mixture; at all events, it has been consohdated here
and there as granophyric or micropegmatitic, interstitial material.

In connection with this resorption and in general with the final consolidation
phenomena R. J. Colony (11) remarks that pyrogenetic effects produced within
the igneous rock itself are partly the result of quot;reactions due to adjustments of
quot;equihbrium between the extreme end-stage, highly concentrated quot;mother-
quot;hquorquot; which, by selective freezing, has been enriched with the more volatile
quot;gases usually termed quot;mineralizersquot;, among which water plays an important
quot;part, and the now almost wholly consolidated rock. These equilibrium ad-
quot;justments, and the changes produced by chemical attack, may be thought of
quot;as an extension of the reaction effects described by Bowen. At this stage much
quot;of the quartz and some of the alkalies, especially soda in such a form as to
quot;appear ultimately as albite, seem to be concentrated in the form of a liquid
quot;consoHdation-residuum, which, from such evidence as is presented in the rocks
quot;themselves, must possess an extremely low viscosity, great penetrating power,
quot;and considerable chemical activity. During the consoHdation of plutonic
quot;rocks especially, the mineralizers operate to effect changes in some of the already
quot;formed minerals, and in some cases cause profound changes in the rock itselfquot;.
The changes of equilibrium occur on account of the different conditions of tem-
perature and concentration, f.i. on account of the abohshment of undercoohng
(see also the remarks of Erdmannsdorffer as referred to above). Such changes
occur in many of the igneous rocks of Aruba and are in general the albitization,
sericitization and epidotization of plagioclase, the chloritization of hornblende,
the chloritization, titanitization and epidotization of biotite. the uralitization of
pyroxene (as far as not the contact uralitization), the zeolitization, the silicifi-
cation. Probably this alteration may be considered in part as a result of hydro-
thermal action, the latter being the continuation of the end-stage magmatic
processes.

The same end-stage hquid (aqueo-igneous matters) which attacked the older
minerals in the igneous rocks also acted on the country-rock which, according to
Colony (p. 177), quot;may be so flooded with quartz, or quartz and feldspar from
quot;igneous sources, as to profoundly change the character of the invaded rocks.quot;
In fact, where on Aruba younger dike-rocks are in contact with older rocks and
where the diorite borders on the older formation, these phenomena can be clearly
seen. The extent of this metasomatic alteration of the country-rock depends upon

the character of the latter and upon the quantity and quahty of the emanation
products themselves.

The younger crystallization products, chiefly the quartzes, show an undulose
or cataclastic character. Therefore, mechanical stresses must have acted during
or after the final consolidation.

In conclusion, there must have been several resorption phases in the con-
solidation of the Aruba bathohthic rocks: 1. that before the crystallization of
hornblende around the hypersthene of the gabbros, 2. that resulting in the
reversal of normal order of zoning with resorption effects of the plagioclases (see
BowEN(7)pp. 274, 275), 3. that before the crystallization of more acid shells in
some of the plagioclases, and 4. that before the final consolidation. The resorption
of (3) is different from that of (4), for the plagioclase shell is more basic than albite
and is older than the quartz.

As to the occurrence of small quartz-bubbles in some of the hornblendes of
the batholithic igneous rocks, reference can be made to B. Asklund (3), who on
p. 35 described the hornblende of certain quartz-diorites as follows: quot;The horn-
quot;blende usually presents a poecilitic character and contains small grains of quartz.
quot;It differs from common hornblende in its brownish-green colour.quot; An equal
texture has been found by Asklund in hornblende-bearing derivatives of noritic
gabbro (he calls it a quot;metamorphicquot; phase, an quot;amphibohtequot;): (p. 22) quot;The
quot;hornblende individuals are mainly studded with small quartz-grains or small
quot;vermicular quartz aggregates, often very thin. This intergrowing structure
quot;clearly recalls myrmekite (quot;hornblende-myrmekitequot;)quot;. — In fact there is a
striking resemblance between this quot;hornblende-myrmekitequot; and the textures
found in some of the Aruba hornblendes; the genesis, however, of the former
texture, as assumed by Asklund, cannot be taken for that of the latter, the
hornblende-myrmekite of Stavsjo being defined by the setting free of SiOg

In the diorites the formation of hornblende took place during the magmatic
stage and resulted in the setting free of quartz, this being (after Bowen (7)
p. 90) quot;a plain inference from the very basic nature of hornblendequot;. And according
to the same writer quot;the hornblende of the diorites has a tendency to include
quot;some of the quartz as small grainsquot;. In this way one may understand the genesis
of the Aruba quot;hornblende-myrmekitequot;. — There seems to be a connection, however
not a very clear one, between the occurrence of this quot;hornblende-myrmekitequot;
and a small amount of quartz in the diorite; that is to say, the quartz inclusions
especially occur in the hornblendes of diorites, more or less poor in or with a
normal quantity of quartz substance; whereas the diorites with rather much to
very much quartz do not show quartz inclusions in the hornblendes. Perhaps
one can understand this, in taking into consideration that, when part of the
diorite-magma-SiOa has been included in the hornblende during earher crystalli-
zation, less SiOa is able to consolidate as younger quartz. However, the youngest

SiOg residual consolidation liquid may have originated, in some cases, not from
the spot itself (being no true differentiation hquid); in that case, on account of the
newly added quartz material, the younger quartz may occur in a greater amount,
even when much quartz is included in the hornblende.

Nevertheless, a better explanation of the quot;homblende-myrmekitequot; puts the
occurrence of quartz-bubbles in hornblende with the autometamorphism in the
diorite magma (see above). That is to say, the residual consolidation liquid, rich
in SiOg, assimilated parts of the already crystalhzed hornblende and, at the same
time, impregnated some of the hornblendes with quartz, so that vermicular,quot;
myrmekite-like textures came into existence. In some rocks this connection
between hornblende resorption and the quartz-bubbles is very striking; see f.i.
the gabbroic quartz-hornblende-diorites A 423—D 12508 and A 448—D 12524.
Similar textures occur in contactzones, being there the result of contact-
metamorphic action (see the hornblendes of transformed hooibergites, gabbros,
diabases; compare with the reaction formulas on p. 95).

It must be mentioned, that in the described quartz-hornblende-biotite-diorites
with quot;homblende-myrmekitequot; no orthoclase was found.

The batholith on Aruba is a differentiated and composite one, which consists of
typical quartz-rich, calci-alkalic rocks. As Daly (12) writes (p. 413), quot;the Tertiary
quot;eruptives associated with the very extensive regions of normal faulting andquot;
quot;subsidence, in the West Indies, are chiefly or wholly of subalkaline, quot;Pacific types''.

The richness in quartz of the igneous rocks, especially of the diorite, must
be the result of fractional crystallization during the consohdation of the magma.
As Bowen (7) has pointed out, f.i. in Chapter VI, separation of early crystals
from hquid (of hornblende, pp. 85, 90; of biotite, pp. 81, S3; or through relative
movement of liquid and crystals) will be the cause of continual lowering of the
temperature ol final consolidation and offsetting in the composition of the
remaining hquid, f.i. towards free silica. Since the batholith may have more or
less a laccolith shape and since the examined rocks have been formed near the
chamber roof, we can accept that the magma has been submitted to a rather
quick coohng and crystallization. This quick cooling and also the orogenic, deform-
ative forces in the bathohth (intrusion during the orogenesis of the older
formation!) must have strongly promoted the mentioned fractional crystallization,
visible now in the zoning of plagioclases and the richness in quartz. As to the '
deformative forces, they acted during or after the late crystalhzation and caused
the undulose and cataclastic nature of the crystals, especially of the quartzes, and
also the faulting of some dikes.

Beside quartz, hornblende is a very important mineral in the Aruba diorites.
The fact that the latter rocks are trae hornblende-rocks, whereas the gabbros
and hooibergites contain much pyroxene, agrees very well with the fact that
hornblende minerals are genetically related to higher temperatures and pressures,
and monochnic pyroxene to lower temperatures and pressures, the gabbros and
hooibergites being roof-crystallizations.

It is a remarkable fact that the peripheric parts of the bathohth
do not show a diorite-porphyritic texture, no more an aberrant marginal texture.
The process of crystallization here was similar to that in the more central parts.
The strong contactmetamorphism of the older rocks also speaks in favour of a
considerable supply of heat to the country-rocks. — The dikes in the bathohth which
do not differ so much from the plutonic rocks, have no sharp borders or „Sal-
bänderquot;, and prove that the invasion took place at a time when these plutonic
rocks were still warm and semifluide; in some cases these dikes even show a
hypidiomorphic-granulose texture.

The sequence in intrusion and consolidation of the various differentiates of
the primary batholithic magma can be clearly distinguished in Aruba: the hooi-
bergites, the gabbroid rocks and the older dioritic rocks intruded and crystallized
before the diorites, the granodiorites and the granites. — The primary batholithic
magma, which was probably a basaltic magma shows a rather great differentiation,
probably because of an ascending of the magma up to a high level (wide range in
temperature and pressures).

According to Bowen (7) pp. 85—91, the quartzdiorite and the granite might
be the product of a fractional crystallization of a noritic gabbro magma (originally,
of primary basaltic magma). — The ideas of Daly (12) concerning the genesis
of norite, hornblende-gabbro, diorite, granodiorite, and granite, being syntectics
of primary basaltic magma and acid country-rock, or the differentiate of such
a syntectic (see f. i. p. 312), do clearly not hold good with regard to the
Aruba plutonic rocks, for the assimilated surface country-rocks present
here are no acid ones (diabases, diabase-tuffs). Probably however, these
acid country-rocks in the sense of Daly's theory are present under the rocks
of the older tormation and can be compared with the gneissose rocks of the
Venezuelan coastrange. — The value of the conception, that the quartzdiorite
is a syntectic of granite magma with diabase, or with gabbro magma, is also
doubtful. — Very probably, the granite can be considered as a differentiate from
dioritic magma; as Daly writes (p. 361) quot;Very commonly, diorite, quartz diorite,quot;
quot;granodiorite passes insensibly into granite in such a way as to suggest that the
quot;granitic magma was a late differentiate from the other magmaquot;. — About the
genesis of the hooibergites and gabbroic rocks, see the chapters in question.
Certainly the crystalhzation of these basic roof-phases must have influenced the
composition of the younger intrusive units.

The dike-rocks must be considered as solid dike-phases of magmas similar
to or differentiated from dioritic magma, that is to say, they bear an aschistic or
a diaschistic relation to the plutonic rocks. Referring to the idea of Daly (p. 384)
it would seem that the basic dike magmas, the melanocratic ones, are direct
differentiates from the primary basaltic magma. In this connection see also
Iddings (21, pp. 292—295) quot;Complementary Rocksquot;.

The predominant E-W strike of the dikes in the batholith rocks - which can
also be seen in the dikes occurring in the older formation - is connected with the
fact that the batholith intruded during the orogenesis of the older formation, the
strike of the axis of folding of the latter being E-W (in this connection, see' the
wrong conclusion of Martin (30) p. 63).

Since the diorite bathohth is younger than the diabase-tuff formation, the
latter has been metamorphosed at its border by the intruding magma. It has been
discussed already before that the uralitization of the diabases and the hornblen-
dization of the tuffs was closely connected with this intrusion. This kind of con-
tactmetamorphism must have acted over a distance of about 2 km from the
visible contact. We have also seen that the uralite-diabases near or in the true
contactzone show more distinct contact-phenomena than the rocks farther from
the contact: contactmetamorphic uralite-diabases. In several places the diabasic
rocks do not border directly on the diorite, but amphibolitic contactrocks (amphi-
bolites, amphibole-plagioclase-rocks), which have originated from the diabasic
rocks in consequence of the process of contactmetamorphism, he here between the
two former rocks. The schistose tuff-rocks too can show strong contact-phenomena
where they lie in the contactzone: contactmetamorphic hornblende-schists. In
other places in the contactzone these rocks only have been strongly invaded. —
Beside exomorphic contactmetamorphism, in some places also endomorphic
contactmetamorphism could be distinguished, and rocks transitional between
diorite and amphibolitic rocks have been found as well. Many of the contactrocks
have a hybrid character, that is to say, they have been strongly invaded by dioritic
material.

In order to prevent the forming of a wrong idea concerning the names con-
tactmetamorphic uralite-diabase and contactmetamorphic hornblende-schist it
must be mentioned once again that the strongly contactmetamorphic rocks in
the true contactzone and the slightly contactmetamorphic rocks farther from the
contact (to about 2 km from the contact) have undergone one and the same
process of contactmetamorphism at one and the same time.

A series of contactrocks has been sampled in the contactzone NW of Shete: A 554,
A 555—D 12581, A 556—D 12582, A 557—D 12583, A 558—D 12584, A 559—D 12585,
with mutual distances of 5 to 10 m. (total length about 30 m). The latter four rocks are
contactmetamorphic uralite-diabases, described above. The rocks A 554 and A 555—D 12581
are normal, orthoclase-bearing quartz-hornblende-biotite-diorites; the many times repeated
recurrence of the plagioclases and the local intergrowth of plagioclase and potashfeldspar in
D 12581 may be connected with the neighbourhood of the batholith roof. - In this contact
diorite and diabase border directly on each other, other contactrocks not having been found
here. It is also remarkable that in most of these contact-diabases pyroxene is still present. -If
we compare the four diabases, the rock D 12585, farthermost from the visible diorite,seems
to be most contactmetamorphic (see the deteriorated texture and the non-fibrous character

of all the hornblende). Yet, it still contains pyroxene, which may have been preserved
in consequence of a quick metamorphism; the latter however must have acted so strong-
ly that a part of the pyroxene could alter into non-fibrous hornblende. The alteration
of D12585 bemg strongest, proves that the contact plane is not vertical and that the
diorite is also present under the diabase. Therefore, no regular changing of properties
in the contact series occurs here.

TACTZONE QUARTZDIORITE-HORNBLENDESCHISTS (plate II, fig. 4)
^ These rocks occur in the contactzone Baranca Corra-Shidaharaka, in the schist-massives
E of Spaansch Lagoen, in the neighbourhood of the diorite-contact near Seroe Boonchi and
near Andicouri.nbsp;'

Macroscopically these rocks are grayish, finegrained and partly schisty. In several of
the samples many small hornblendes can be distinguished.

Microscopic description: The rocks consist of a very finegrained, plagioclase-rich horn-
blende aggregate, with many bigger hornblende crystals. The matrix is composed of a felt
of hornblende needles and prisms, in which small plagioclase grains occur, here and there
lamelled, and simply zonal. It is remarkable, that, in contrast with the normal metamorphic
tuffs, the hornblende aggregate in the DD perpendicular to the cleavage-planes of the schisty
rocks IS diverse and not parallel. - Beside a more or less regular distribution of hornblende
and plagioclase, the rocks D 12639, D 12652, D 12662, D 12670 and D 12676 show an irreg
ular alternation of both minerals, the plagioclase occurring as an aggregate in veins or in
more or less parallel quot;lensesquot; (magmatic invasion). The transition between plagioclase mass
and hornblende felt is rather abrupt or gradual. At all events, many hornblende needles stick
and he in the plagioclase aggregate. The latter moreover contains in D 12652 some chlorite
and epidote, in D 12662 big Pepidote flocks. The composition of the plagioclase is about
ohgoclase-andesine to andesine. Beside the plagioclase D 12649 locally contains some quartz
Ore is abundant in most of the rocks: magnetite and titanomagnetite. Some rocks contain
nests of epidote

A few tuff relic-crystals of andesine occur in the matrix of D 12639, D 12649, D 12662
D 12663 and D 12676. They are partly idiomorphic, here and there twinned or zonal and
rarely altered (Popalized in D 12663). The hornblende needles of the matrix stick in many of
them. If we compare these rocks with the normal metamorphic tuffs, we see that in the
former the number of plagioclase relic-crystals is smaller than in the latter, and also that
the plagioclases of the former have been more hornblendized than those of the latter So it
seems, that a number of relic-crystals in the contactmetamorphic rocks have quite disappeared
during the strong contactmetamorphism. In D 12639 a few roundish parts are greener than
the rest of the matrix and consist of a coarser hornblende felt plus ore. May be these parts
originated from rock inclusions.nbsp;'

The clear exomorphic contact-phenomenon in these rocks is the occurrence of many
rather big, new-made hornblende crystals, which are generally idiomorphic prisms and
needles, with the normal hornblende-cleavage. Yet, many of the prisms and needles show
fryed ends. The hornblendes are Hght-greenishbrown, light-brownishgreen to almost
colourless m D 12652 and D 12663; green to lightgreen in the other rocks Part of the crystals

Pquartz-bubbles. The arrangement of the hornblendes
in D 12662 is here and there as in amphibohtes. The hornblende felt takes up more room
than these hornblende crystals. Generally, the quantity of the hornblende crystals decreases
with increasing distance from the contact. - The big hornblendes occur in too large a number
for them to have originated from pyroxene crystals of the original tuffoid rocks At the
utmost, only a few of them originated from such pyroxenes. The greater number of them
is new-made, perhaps totally out of tuff material, perhaps also by supply of magmatic
material out of the dionte magma (compare with the invasion of plagioclase material) -
Hence, may be this contactmetamorphism is not only a thermal one but also a hydrothermal-
pneumatolytic and injection metamorphism.

As to the invasion of plagioclase material, these rocks must have been invaded and
soaked with magmatic or hydrothermal solutions during the intrusion of the diorite batholith;
these solutions must have intruded along fissures, formed by orogenesis, and must havé
resorbed the rocks locally. The fact that hornblende needles lie in the plagioclase veins means
- as we have seen already above - that the process of hornblendization proceeded still after
the intrusion of the veins.

A 652—D 12652: E of Baranca Corra; A 662—D 12662: just N of Baranca Corra; A 663
—D 12663: between Baranca Corra and Shidaharaka; A 670—D 12670: just N of Shidaharaka;
A 639—D 12639: E of Spaansch Lagoen, W of Shidaharaka; A 649—D 12649: Seroe Boonchi'
A 676—D 12676: Andicouri.

Professor J. A. Grutterink sampled a pebble in Rooi Taki, E of Spaansch Lagoen,
which proved to be a contactmetamorphic, variolitic hornblende-schist (metamorphic
variolitic tuff). This rock (no. 3285—D 2337) is a normal contactmetamorphic hornblende-
schist, the variolitic character of which manifests itself because of the fact that the number
of new-made, secondary-idiomorphic hornblende crystals is much smaller m the varioles
than in the interjacent mass. So, there must have been a primary difference between the
composition or texture of the varioles and that of the interjacent mass.

SOME CONTACTROCKS BETWEEN QUARTZ-DIORITE AND HORNBLENDE-
SCHISTS (METAMORPHIC TUFFS)

A series of rocks has been sampled in the contactzone N of Seroe Blanco (near Spaansch
Lagoen), where diorite and metamorphic tuffs border on each other: The samples have been
taken in a direction perpendicular to the contact line, over a distance of about 40 me

A 717—D 12685 is a normal quartz-hornblende-biotite-diorite with a many times
repeated recurrence in the plagioclases and with normal alteration and distortion of the
minerals.

A718—D 12686 is an altered quartz-diorite. Macroscopically the rock looks strongly
altered; the dark minerals occur more as stretched masses than as crystals. Under the microsco-
pe it shows a slightly parallel structure, and an oppressed hypidiomorphic-granulose texture.
Its dark minerals have been totally chloritized. The plagioclases intensively work in with
quartz in several places, and are strongly bent or undulose. They are quite albitized. strongly
epidotized and less sericitized. The quartz is present as bigger grains, strongly undulose to
cataclastic; .and as finegrained aggregates as well; narrow chlorite layers are woven between
the stretched grains of these aggregates. The chlorite occurs with epidote and titanite as
more or less stretched masses, and has velvet-like greenishbrown and steelblue interference-
colours. or is isotropic. It originated partly, perhaps wholly, from hornblende (hornblende-
cleavage); may be, part of it originated from biotite (chlorite together with titanite).

It is questionable whether the above-described alteration is due to contactmetamor-
phism. In fact, other diorites, sampled far from the contact, show the same alteration minerals
and also, to a certain extent, effects of stress. On the other hand, the distortion in this
contact-diorite is so strong that it seems to have had its origin in the quot;collisionquot; between the
optrusive and intrusive diorite and the solid tuff (and diabase) mass.

A 719—D 12687, A 722 and A 723 are quartz-plagioclase-epidote-chlorite-rocks; greeny,
schisty and breccious. D 12687 shows a kind of banded structure, that is to say, plicated
layers of epidote with some quartz lie between breccious layers, of unequal thickness, of
plagioclase and quartz. These breccious layers contain many fragments of strongly squeezed,
undulose and bent albites; narrow layers of strongly undulose, stretched quartz grains aré
woven between these plagioclase fragments. The latter lie in an any-given way with regard
to the parallel structure of the rock. The narrow quartz layers contain epidote and chlorite,
the latter with greenishbrown interference-colours and occurring as stretched, fibrous masses,'
which follow the curves of the quartz layers. Magnetite is rare. - These rocks represent né

compressed and altered diorites, but probably are the product of solutions (quartz-epidote,
which took up diorite plagioclases and crystallized under pressure to a banded-structured

A 720-D 12688 is a quartz-epidote-vein-rock with a kind of banded structure- layers
of undulose and dusty quartz alternate with quartz-epidote and epidote-quartz aTers The
epidote IS brownyellow. Locally, bundles and felt-like aggregates oïtiny hornblendrneelles
occur enclosed in the quartz aggregates. - This rock is also a magmatic or hXtherma
produc , crystalhzed under pressure to a banded-structured quar'tz-epidote-roS

banded structure; lenses and layers of albite-oligoclase, with many hornblende needles oLr

J hornblendes occur which are long- and thin-prismatic, non-fibrous and cleaCedquot; tS

contactmetamorphism. Parallel strings of epidote and titanite are also present. - This rock
he co^n act' Itquot;' quot;nbsp;described on p. 23. which have been sampled farther from

hornblende-schists on p. 99; that is to say. the bigger new-made hornblendes, so abundant in
the above-mentioned rocks, are present in but a very small number here

It must have intruded even during the process of folding and must have consolidated under
pressure (see the structure). The hornblende needles, chloritized or not, which occur in the
veins, may have come into existence in consequence of the hornblendization process which
was not yet fmished at the time of the vein intrusion, or may have loosened frL the W
blendematrixofthemvadedmetamorphictuff-rock and enclosed in the veinmaterial- in the

in sh^r! , veinmaterial must have intruded after the process of hornblendization had
tinished (see also the discussion on p. 100).

Hence, this series of contactrocks does not show strong contact-phenomena
At best, the contactmetamorphism was an endomorphic (?) and exomorphic
pneumatolytic-hydrothermal Contactmetamorphism, whereby the original tuff-
rocks were partly replaced by magmatic or hydrothermal material As has been
manifested above, even the hornblende-schist A 721—D 12689 shows no strong
contact-phenomena.nbsp;^

In connection with the above-described contactrocks, some other contactrocks will be

tuffoid rocks) have been metamorphosed by a quartz intrusion. A 673-D 12673 occurs

about 30 cm. from the dike. A 174 is an epidote-bearing quartz-rock and lies between the
quartz dike and A 672. The rocks merge gradually into each other. - D 12673 cons strmaiii;

grains epidote aggregates and some hornblende and oligoclase relic-crystals The rock is
somewhat banded-structured because of some layers and lenses of undulose qua;tz with some
chlorite and hornblende fibres enclosed. - D 12672 shows a kind of banld strTctu rof
brownish epidote and undulose. parallel-granular quartz. The epidote layers local
a parallel-structured hornblende aggregate and also bigger hornblendes

N of^Snat ^J^'^^j^^-^P^^^^-^^blende-s^^ A 628-D 12628, sampled near the contact and
N of Spaansch Lagoen. Quartz dikes occur in a great number here. The structure of this
schisty rock is a little banded. SpheroHtic chlorite with brownishgreen! TTZXe,

interference-colours and grainy epidote occur alternately (banded) or mixed. Moreover, small
prismatic hornblendes, locally in a great number, some quartz and rare magnetite are present.
— In the close neighbourhood of these rocks also invaded chlorite-epidote-schists (A 686)
and invaded hornblende-schists (A 685) occur.

3.nbsp;A quartz-chlorite-schist A 675—D 12675 has been sampled as the country-rock
of gold-quartz-dikes on the Mira la Mar, near the diorite contact. The rock feels fat and is
lustrous, schisty and green; it shows a minute folding. It is a finegrained quartz mass with
much chlorite and calcite, which occur as quot;flamesquot; through the rock (in the sample the
darkgreen spots). Moreover some magnetite and brownish leucoxene are present; the rock
has been invaded by quartz-calcite.

4.nbsp;In a place NNE of Spaansch Lagoen too contactrocks have been sampled; A 180
and A 181 are strongly altered diorites which merge gradually via quartz-albite-chlorite-
epidote-rocks (A 185, A 186) into invaded hornblende-schists.

5.nbsp;From the contactzone WNW of Mira la Mar two rocks are known which occur but a
few m. from each other: A 709 is an altered quartz-hornblende-diorite, A 708 a chloritized
hornblende-schist.

6.nbsp;In the diorite NNW and N of Spaansch Lagoen rocks transitional between diorite
and hornblende-schists have been found in several places. These rocks have different strikes
f.i. N 65 E, N 85 E, N 120 E and have a very steep dip. They are quartz-albite-chlorite-epido-
te-rocks (A 173, A 183, A 724, A 725) and border on diorite or on quartz dikes. This diorite
is altered in the close neighbourhood of the schisty rocks and is greeny there.

1. Rocks transitional between contactmetamorphic uralite-diabase and amphibole-
plagioclase-rock.

Contactmetamorphic uralite-diabases have been described before. In connection here-
with two rocks will be described from the hill E of Malmok (NW-Aruba) which are still more
metamorphic: A 486—D 12550 and 3394—D 2444 (Delft collection). The rocks consist for the
greater part of hornblende. An ophitic texture can be recognized but here and there, although
the bulk of the laths do no more exist as such and are composed of a grainy anorthite aggre-
gate. These plagioclase aggregates lie also as irregularly shaped masses between the horn-
blendes and contain big flocks of Pepidote. The hornblende is mainly developed as rather big,
irregularly shaped crystals, non-fibrous and partly cleaved or twinned. The crystals are
frayed, and numberless diminutive hornblende needles and prisms occur in the bigger
crystals and in the plagioclase aggregates. A few small hornblendes are secondary, idiomor-
phic and occur especially in the bigger crystals. The common accessory minerals are present.

In A 778—D 13076 (Mira la Mar) we see quartz-hornblende-biotite-diorite with an
inclusion of strongly contactmetamorphic uralite-diabase, transitional into amphibole-
plagioclase-rock. The diorite forms a dike in diabase and partly resorbed the inclusion.
Microscopically the rocks are not sharply bordered. In the diabase an ophitic texture can be
recognized with difficulty. The plagioclases have been totally albitized (the diorite plagioclases
are also albite!) and strongly sericitized and epidotized. The many new-made hornblendes
lie locally so close together that the diabase has an amphibolitic character in such places. The
hornblende is here and there chloritized. Titanomagnetite is present in grainy groups. Some
quartz and totally chloritized biotite may be diorite material.

No. 3376—D 2426 (Delft collection), sampled on the beach between Bushiribana and
Rooi Fluit, probably at Andicouri, is an amphibole-plagioclase-rock, transitional between
diabase and amphibolite. It is a massive, granoblastic rock with hornblende and plagioclase
in about the same amount, regularly distributed. The hornblende occurs, alternating, as
well-cleaved amphibolitic hornblende and as lightgreen, fibrous and partly chloritized
hornblende. The basic plagioclase, locally simply zonal, is granular or more lath-shaped, and
is in many places diablastically intergrown with the hornblende. The texture has still here

So. in this series of rocks the texture changes gradually from a diabasic into an amnhi
bohtic one; here and there together with an increase in hornblende amount ^

Some of the contactmetamorphic uralite-diabases, described together with the uralite

D 2290 (Delft collection; NW of Rincon) also contains pyroxene, however in a se^ndary phase

a most totally deteriorated ophitic texture. There is less plagioclase than hornblende The
plagioclase is present for a small part as laths, and mainly as a finegrained ag^r ga e beL^^^^^

features. The structure is massive to slightly parallel. Hornblende and plagioclase occur in
the same way as in 3376-D 2426 (see above). The diopsidic pyroxene is tL thTrd m la)

The amphibohtes are no normal amphibohtes as have been described f i
byGRUBENMANNfl9),but-as we shall see below - must be considered as
contactmetamorphic rocks. It is better therefore to add the name amphibole-
plagioclase-rocks, some of the here-described rocks being rather different from
true amphibohtes and looking more like real contactmetamorphic rocks. Although
he rocks show certain points of distinction, they can, nevertheless, be brou/ht
together m this chapter.nbsp;^

D 12601; A 588-D 12602; A 589-D I2603; A 590-D 12604; A 591-D iS A
D 12606; A 603-D 12607; A 604-D 12608; A605-D 12609: ASLS S-' A 6n ~
D 12613; A615-D12615; A616-D12616; A617-D12617; A 61LS 2618: t
D 12625; A 626-D 12626; A 627-D 12627; P 79-D 6545.nbsp;'

Macroscopic description: The amphibolitic rocks are fineeraineri tn r ■ ^
generally darkcoloured (grayish, greenish, brownish). The col^ Spe^^^^^^^^
the degree of alteration (quot;imbibitionquot;). Most of the samples show a more orts scSty haWt
The rocks A 550, A 566. A 576. A 589. A 590. A 592 and A 618 hnwXlt ^
gramnar^ The rock A 587 shows moreover a banded and also spotted^^^^^^^^^^^^^
a spotted structure; small black spots are lenses of quot;unaltered'' .Z JTvTnbsp;has

Microscopic description: The structure is parallel in most of the rocks- the parallellism
however, differs for each of them. The hornblende crystals lie rou^hlv ^I'l 1
D 12600 and D 12608 show a rather good parallelliSx a kin^of baS
seen in D 12601 and D 12605. That in D 12601 is chamcttquot; Ih K 1
to long-lens-shaped, darker and lighter green isses t^^^^^^^^^^^^^^^nbsp;quot;

The texture is crystalloblastic. Moreover, it is granoblastic in most of the rocks (also in
the rocks with massive structure). Exceptions are D 12600, D 12601 (granoblastic with a
tendency towards nematoblastic), D 12608, D 12625 and D 6545 (granoblastic to
nematoblastic).

Main constituent minerals: The amphibolites consist mainly of hornblende and plagio-
clase. The hornblende takes up more room than, about as much room as and rarely less
room than plagioclase. The rocks with very much plagioclase and also those with a certain
amount of quartz have been secondary enriched with plagioclase and quartz material, very
probably (see p. 105). The crystals are, in general, regularly distributed. The hornblendes in
D 12577 are much bigger than the plagioclase crystals. D 12602 and D 12616 contain in a few
places groups of bigger hornblendes. D 12617 shows more or less lens-shaped parts, which
consist mainly of hornblende; these parts lie in an amphibolitic mass, that contains a little
more plagioclase than hornblende and that seems to be enriched. There is no fundamental
difference, however, between both kinds of amphibolite, which merge. Ore can be found in
by far the most of the rocks.

The hornblende is the common green hornblende. In some rocks this mineral is light-
green to very lightgreen; brownish-green and almost colourless crystals are not widespread.
In most of the rocks the crystals are grainy and short-prismatic. D 126C0, D 126 8 nd
D 6545 contain prismoid-granular to columnar crystals (long prisms). Beside the common
hornblendes very small hornblende needles are present in some rocks; they lie and stick in
the plagioclase. - The prismatic crystals are but for a small part quite idiomorphic. The
cleavage of the hornblendes is the normal one and their crystal borders are non-frayed.
Several of them show twinning. Many of the hornblendes contain diminutive quartz-bubbles,
which seem to be connected with the presence of foreign quartz material in many of these
rocks (see p. 105).

The plagioclases are in general fresh. In some rocks they contain some epidote and
sericite, in connection with the neighbourhood of narrow epidote veins. The plagioclases are
granular, rarely prismatic. They occur between the hornblende crystals and do not show own
forms. The plagioclase in D 12589 locally occurs in aggregates. The same rock also contains
a few laths. In D 12600, D 12601, D 12602, D 12605 and D 12609 plagioclases are somewhat
diablastically intergrown with hornblendes, or show a tendency towards such an intergrowth.
This kind of texture may be considered as being connected with the ophitic diabase texture
(see also p. 102). Only a few crystals show twins or lamels. A few plagioclases show a zonal
extinction. The composition of most of the plagioclases is oligoclase-andesine; others are
andesine, andesine to labrador, labrador. The plagioclase of D 12589 is bytownite. D 6545,
D 12610 and D 12616 contain albite-oligoclases, D 12595 and D 12618 albites. There is a
close connection between the composition of the amphibolite plagioclase and that of the
plagioclase of intruded material (see below). - D 12605 and D 12617 contain a few bigger
crystals, which may be relic-minerals; those of D 12617 enclose hornblende needles.

In some rocks apatite occurs as small needles, especially in the plagioclase. - Magnetite
is of a non-frequent occurrence or of a very minor importance in the greater part of the
rocks. Other rocks contain much ore as bigger and as many diminutive grains. The ore rarely
contains leucoxene (titanomagnetite).

A few and small plates of biotite can be found in D 12617. Chlorite in D 12605 may be
newly added or may have originated from hornblende. - D 12600 shows a curious and narrow
quot;Quetschquot;-zone, perpendicular to the parallellism; the hornblende crystals in this zone show
a very good cleavage.

These amphibolitic rocks always occur in the neighbourhood of the contact, in the NW-
corner of the island, in the surroundings of Andicouri and of the Santa Lucia, and — for a
small part - in the Seroe Pretoe, N of Savaneta. A 566 occurs on Mira la Mar, A 550 near
Baranca Corra and A 576 NW of Rincon i).

1) Kloos (25) described some amphibolites. The rock 106* is an amphibole-plagioclase-
rock enriched with diorite material. The rock 144 has been abusively called by him a fine-
grained diorite variety; it is an invaded and enriched amphiboUte.

Except A 550, A 590 and A 617, the above-called amphibolitic rocks have been enriched
with quartz and/or have been invaded by dioritic material.

The rocks are more or less strongly invaded by magmatic and hydrothermal veins, which
are leucocratic. The veins do not only lie parallel to the schistosity. Some rocks have been
invaded very strongly so that lenses and layers of the amphibolite lie enclosed in a mass of
invasion material.

Except in the rocks D 12600, D 12603, D 12605, D 12615, D 12618 and D 6545, quartz
as non-undulose grains between the amphibolitic minerals is present in a smaller or greater
amount. The quartzes of D 12601 are partly intensely intergrown with plagioclase and
hornblende; the quartz-bubbles in the hornblende are clearly connected herewith.

Some rocks only contain veins of epidote, with or without quartz and chlorite. Most of
the rocks, however, also show aplitic veins (dikes). The latter are not sharply bordered on
the amphibolitic rock, but merge gradually or more abruptly into this rock. Hence, there is
a difference in composition between the central and peripheric parts of such veins. The veins
in the various rocks also show differences in composition. - The plagioclase of the true
diorite-aplitic veins (dikes) varies in composition from albite to andesine, and is rarely zonal.
The quartz is here and there slightly undulose. The hornblende, if present, is irregularly
distributed and looks as if it had been taken up from the amphibolitic rock; if the hornblende
really does not belong to the aplitic invasion material, it must have been taken up during the
genesis of the amphibolite. It occurs as prisms, needles or grains, many of which contain
quartz-bubbles and some of which have been partly chloritized. — The vein of D 12613 con-
tains several very big hornblendes which enclose many small plagioclase and quartz grains
(sieve texture), and also contains a diverse-fibrous hornblende aggregate. — The vein in
D 12626 shows parallel layers of accumulated hornblende crystals, obviously parts of the
amphibolitic rock. Accessory minerals in the veins can be magnetite and apatite, possibly
also amphibolitic minerals. - The vein in D 12600 contains the same minerals as the amphi-
bolite, but relatively much more plagioclase; some curious, irregularly shaped apatite grains
are also present. - The vein in D 12603 consists of grainy plagioclase which is oligoclase-
andesine at the borders of the vein (the same composition as in the amphibolite) and albite-
oligoclase in the centre. - The veins in D 12608 are plagioclase veins with some hornblende,
green biotite and magnetite. The part of the amphibolite which borders on the vein, contains
more and bigger hornblendes than the normal amphibolite farther from the vein; in this
part the structure is not so clearly parallel, and the hornblendes contain Pquartz-bubbles. -
In D 12618 we can see spots with more plagioclase than in the normal rock, and with small
hornblende needles and ore. They form the transition into veins of grainy and dusty albite. -
Some hornblendes near and in the quartz veins of D 6545 have been chloritized. - D 12616
contains, amongst others, a quartz vein, part of the grains of which show quot;Streifen.quot; These
quot;Streifenquot; and also the planes of fluid-inclusions occur mainly perpendicular or parallel to
the vein borders. - The veins here and there manifest faults in the amphibolitic rock f i
in D 12605.nbsp;' quot; '

STRONGLY ALTERED AND INVADED, PARTLY ABERRANT AMPHIBOLITIC
ROCKS (AMPHIBOLE-PLAGIOCLASE-QUARTZ-ROCKS)

Under this title rocks will be described which still show much affinity to the described
amphibohtes, but which have been strongly enriched and partly have a different texture.

, A 624—D 12624 (near Santa Lucia) is a pink rock with darkcoloured. parallel layers of
small hornblende crystals and magnetite in a granoblastic mass of plagioclase (oligoclase-
andesine) and quartz. The grainy hornblende, green to colourless, with many quartz-bubbles
occurs also outside the mentioned layers and between the other minerals. Apatite. Limonite
occurs between the crystals (pink colour).

A620-D 12620 (just S of Tibusji Goudmijn) is an amphibolite with a hardly parallel
structure and which has been strongly enriched with quartz and plagioclase (labrador).
In a fine-granoblastic mass of palegreen hornblende, plagioclase, quartz and a few small

partly chloritized biotites many bigger, irregularly shaped, green hornblendes occur which
are more t^vmned and contain more quartz-bubbles than the smaller ones (see also the dark
spots m the sample).

A 548—D 12575 (NW of Annaboei) is a massive-structured, granoblastic rock rich in
ore and enriched with quartz and albite. The hornblende is almost colourless to palegreen
and partly limonitized. Small aggregates of brown-green biotite occur in the neighbourhood
o the hornblendes. The rock has been invaded by quartz-albite material with some horn-
blende and magnetite; the latter two minerals probably belong to the amphibolite

A 623-D 12623 (E-slope of the Santa Lucia) is a massive, granoblastic amphibolite, the
hornblende of which is partly normal and partly irregularly shaped, lighter green, fibrous
or chloritized. These two kinds of hornblende have the same distribution. The plagioclase
(labrador) partly occurs as some bigger, non-idiomorphic, strongly altered crystals

A 577-D 12596 (between Rincon and Quadirikiri) looks in the sample like a dark
diorite; the dark parts are very finegrained amphibolite and hornblende crystals In the
slide we see parts of massive, granoblastic amphibolite which gradually merge into the rest
of the rock. The plagioclases of the amphibolite are simply zonal oligoclase-andesines- the
hornblendes of the borders of the amphibolitic parts contain small plagioclase grains For
the rest, the rock consists of an aggregate of zonal andesines with many, rather big and irregu-
larly shaped hornblendes, which enclose many plagioclase grains (sieve texture) These
hornblendes are light-to browngreen, partly chloritized. Locally, big quartzes occur, which
also enclose small plagioclase crystals. Moreover, much ore and a little titanite are accessory
A 573-D 12592 (NW of Rincon) looks a little dioritic and is locally almost exclusively
a coarse hornblende aggregate. A narrow aplitic dike merges into the lightcoloured parts of
the rock. In the slide, very big, normal hornblendes enclose numerous small plagioclase
grains with a varying orientation (sieve texture). Between these hornblendes a finegrained
albite aggregate occurs, with secondary minerals and locally with quartz. On the side of the
mtrusion the rock looks more dioritic: normal, prismatic hornblende, idiomorphic albites
and allotriomorphic quartz. Ore is rather abundant.

These rocks must be considered as dioritized amphibolitic rocks, that is to say, these
rocks must have been flooded in such a way by magmatic material that they have lost
their amphibolitic character.

The rocks A 612—D 12614. A 621—D 12621 (E of Plantage Westpunt). A 619—D 12619
(near Druif, NW Aruba), A 549-D 12576 (NW of Annaboei) are darkcoloured, finegrained
rocks, invaded by dioritic material; they are allotriomorphic-granulose. The plagioclase is about
the same as diorite-plagioclase, and its composition varies from oligoclase to labrador- some
of the crystals are clearly bent. Some plagioclases in D 12614 and D 12619 contain microlitic
inclusions in the core. The hornblendes are granular to short-prismatic, rarely idiomorphic
and part of them contain quartz-bubbles. They lie here and there in groups, and as very
small crystals in the plagioclase. Except in D 12621, quartz is present in a smaller or greater
amount. D 12614 contains a few very small grains of diopsidic pyroxene and a single crystal
which seems to have been uralitized along the borders and fissures. Apatite, magnetite and
titanite are accessory. - The rock in D 12621 merges into dioritic dike material of plagioclase

A 607—D 12611 (E of Plantage Westpunt) is an orthoclase-bearing quartz-hornblende-
biotite-diorite merging into a finegrained, dioritized amphibolitic rock. The diorite is rather
rich in quartz and rather poor in dark minerals; the altered amphibolitic rock is poor in
quartz and rich in hornblende and does not contain orthoclase. Both rocks have a hypidio-
morphic-granulose texture. The hornblende in the altered amphibolitic rock is partly present
in groups of small crystals; quartz quot;dropsquot; occur in and between the grains of these groups
The same rock also contains a very little biotite.

A 563-D 12586 (Sabanilla Abau, SE of Santa Lucia) shows short plagioclase prisms

with microhtes and recurrence-zones in a finegrained quartz-plagioclase aggregate. This
aggregate also contains irregularly shaped hornblendes and more aggregates of hornblendes
with numberless quartz-bubbles. In some of these aggregates pyroxene cores can be seen.
Chlorite may have originated from hornblende and from biotite. Ore is rather abundant.

Appendix: A 779—D 13077 is an aberrant amphibolite S of Seroe Boonchi, near the
contact. The aberrant characters are 1) nematoblastic texture, 2) richness in ore, 3) acidity
of the plagioclase (oligoclase) and 4) the presence of several bigger relic-crystals of strongly
altered plagioclase and hornblende, around which the small hornblende crystals curve.

Dependent on the smaller or greater amount of plagioclase, the following rocks belong
to the former or to the latter group. The rocks are greenish-gray, finegrained and more or
less schisty.

A 754—D 13061 (Salinja Druif) and A 755—D 13062 (near Andicouri) are hornblende-
gedrite-schists, massive and nematoblastic. They consist for by far the greatest part of
common green hornblende and gedrite, and contain but very little grainy plagioclase and
quartz. The amphiboles are palegreen to almost colourless prisms, needles and columns of
a varying size, which lie in diverse-fibrous aggregates or in radial bundles. The crystals are
sound-bordered or frayed. Some of the common hornblendes are twinned. Chlorite occurs here
and there between the amphiboles. Magnetite is present as a few grains and crystals.

A 758, A757—D 13064 (Salinja Druif) and A610—D 12612 (E of Plantage Westpunt,
NW-Aruba) are rocks, transitional between hornblende-gedrite-schist and hornblendite-ge-
dritite.They are massive and roughly parallel-structured, grano- to nematoblastic, and consist
for the greater part of common hornblende and gedrite with a little plagioclase and quartz.
The common hornblende is green to lightgreen, granular to prismatic, well-cleaved and
partly twinned. The gedrite is almost colourless to very palegreen, long-prismatic to colum-
nar. The amphiboles are sound-bordered and contain many quartz-bubbles. The plagioclase
is granular and contains many hornblende needles; it is partly-lamelled oligoclase-andesine
(D 13064) and labrador (D 12612). A few small biotite plates and magnetite grains are also
present. Quartz is a secondary, added mineral (see also the quartz-bubbles in the hornblende)
and occurs in D 13064 as grains, in D 12612 in nests. The latter rock contains vein material,
merging into the amphibole aggregate; it is an allotriomorphic-granulose quartz mass with
plagioclase, some hornblende and ore.

A 756—D 13063 (near Salinja Druif) is a rock transitional between gedrite-schist and
gedritite. It is a roughly parallel- and slightly banded structured, nematoblastic rock with
much more gedrite than plagioclase. The gedrites are very palegreen, sound-bordered prisms
columns and needles, with Pquartz-bubbles. The plagioclase grains contain many gedrité
needles, and are partly-zonal andesines. Some biotite and magnetite.

These rocks too must be considered as contactrocks, occurring in the contactzone of the
diabase.

The rocks A 575-D 12594, A 584-D 12599 and A 622-D 12622 are darkcoloured,
finegrained, massive-structured and granoblastic, in general amphibolitic.

D 12594 (NW of Rincon) consists of normally amphibolitic hornblende and plagioclase
(oligoclase-andesine), many grains and short prisms of palegreen, diopsidic pyroxene, irregu-
larly distributed and locally accumulated, and a little magnetite. Veins of plagioclase.

D 12622 (Seroe Pretoe, N of Savaneta) contains hornblendes of a varying size a little
plagioclase (labrador-bytownite), apatite and magnetite. The diopsidic pyroxenes' have a
varying size, and are colourless to very palegreen grains and prisms, rarely twinned They
occur especially in intergrowth with hornblende (partly urahtized?). The rock merges into

invasion material which is an aggregate of plagioclase grains (labrador-bytownite), working
in with each other; the latter show a quot;Schachbrettquot; texture and contain quartz quot;dropsquot;
(sieve texture). Locally, bigger quartzes occur between the plagioclases. Flocky epidote is
present. The transition part between the two rocks contains normally grainy plagioclase,
small prisms and needles of hornblende and grainy pyroxene.

In D 12599 (NW of Arikok) the amphibohte, consisting of hornblende, less diopsidic
pyroxene, plagioclase and a little ore, merges gradually into a grainy pyroxene aggregate
with ore. At the same time the size of the grains decreases. The amphibolitic rock contains
a little more hornblende and pyroxene than plagioclase (andesine). The two former minerals
contain bubbles of ? Veins merge rather abruptly in the described rock and consist of plagio-
clase with or without epidote, sericite, quartz.

A 574—D 12593 (NW of Rincon) is a reddishbrown weathered, darkcoloured, crystalline
rock. Big, green hornblendes, big, colourless to very palegreen, diopsidic pyroxenes and big
quartzes contain numerous small grains and crystals of labrador, several of which are simply
zonal (sieve texture). In several places the plagioclases occur in aggregates, and also a few
bigger prisms are present. Magnetite is abundant. The pyroxene shows limonitization and
here and there a fibrous alteration.

Thedarkpartof A 582—D 12597 (SW-foot Seroe Boonchi) contains big hornblendes, with
many plagioclase crystals enclosed. The small hornblendes and plagioclases constitute an
allotriomorphic-granulose texture. Locally, between and in the hornblendes small diopsidic
grains occur, with a narrow hornblende rim. Magnetite is widespread. This rock gradually
merges into a quartz-rich, aberrant diorite-rock. The hornblendes of this diorite are big,
irregularly shaped and contain many roundish to prismatic plagioclases and a very few
grainy quartzes (a single quartz is idiomorphic). This hornblende also contains a little chlorite.
A single hornblende in the transitional zone contains quartz-bubbles.

J. H. Kloos (25, p. 28) abusively described the rock 141, sampled by Martin near Arashi
(NW-Aruba), as an augite-diorite. It is a quartz-plagioclase-diopside-hornblende-ore-rock
with a dike of diorite. The pyroxene is granular. The few hornblendes occur as irregularly
shaped individuals and also as grainy crystals.

Appendix: Locally in the contactzone of NW-Aruba aphanitic to finegrained rocks have
been sampled, which are very rich in quartz and epidote, but which do not occur as dikes or
veins. Probably they must be considered as contactrocks.

J. H. Kloos (25) abusively described on p. 27 the rock 140 (near Arashi) as an augite-
diorite. It is a quartz-chlorite-epidote-hornblende-ore-rock with here and there amphibolitic
parts. The hornblende occurs as small, idiomorphic or frayed prisms, locally with quartz-
bubbles. Many very big ore individuals have a grainy titanite rim. Apatites.

A 108—D 12075 (E of Malmok) is an epidote-quartz-ore-rock with some chlorite, apatites
and narrow quartz veins.

Similar rocks have been found, probably as inclusions, in the diorite. A 749—D 13056
(ESE of Turibana) is a quartz-epidote-hornblende-biotite-chlorite-rock with a little ore. In
one part of the rock hornblende occurs (as small, frayed prisms), in the other part greenish-
brown biotite and yellowish chlorite. A 776—D 13074 (in the quot;rooiquot; S of Seroe Sumpina.
near Seroe Crystall) is a quartz-epidote-albite-hornblende-rock with magnetite, apatite,
titanite, and epidote veins. The albite is here and there intensely intergrown with quartz.
The hornblende occurs as many long, twinned prisms, green and cleaved, locally accumulated.

In several places in the contactzone between diabase and diorite the transition
diabase diorite has been studied. Since the contact plane is not vertical,
but in many places slowly dips in the direction of the diabase, and since in conse-
quence hereof the diorite underlies the diabases, which are the roof of the

batholith^), the contactzone crops out here and there as a very wide zone. So f.i.
in NW-Aruba and S of Andicouri the great distribution of amphibohtic rocks
proves that not far down there the diorite is present and that the contact plane
in general must lie about horizontal. In many places too, the contact plane is
very irregular, and the diorite sticks in many big tongues in the diabase. Therefore,
many of the contacts do not show a regular transition from diabase to diorite in
the samples.

1.nbsp;Contact amphibolitic rocks and diorite E of Plantage Westpunt, NW-
Aruba. The samples have been taken here over a distance of about 285 meters
in a direction N 160 E. From N to S: a amphibolite (A 603, D) f30m.) b en-
riched and invaded amphibolite (A 604, D) (30m) c the same (A 605, D)
—^ (30m) d the same (A 606, D) (6m) e small outcrop of quartz-hornblende-
biotite-diorite with inclusions of dioritized amphibohte (A 607, D; A 608; A 609)

(65m) / invaded hornblendite-gedritite (A 610, D) (30m) g strongly
invaded amphibohte (A 611, D)(55m) Ä rock transitional between amphibo-
hte and diorite (A 612, Dj (15m) «a leucocratic dike, a few m. wide (25m)
ƒ quartz-hornblende-diorite (A 613).

2.nbsp;Contact diabase and diorite NW of Annaboei, NW-Aruba. The following
rocks have been sampled here: a contactmetamorphic uralite-diabase (A 547, D)-
b enriched and invaded amphibolite (A 548, D); c rock transitional between amphi-
bolite and diorite (A 549, D); d strongly altered diorite (A 546—D 12573). The
plagioclases of the latter rock work in with the quartz here and there or are gran-
ular in groups, and contain ore and numerous quartz quot;dropsquot;. Its hornblende
mainly occurs in groups of small crystals with quartz-bubbles and as many
needles and grains in the plagioclase.

3.nbsp;ContactdiabaseanddioriteNWof Arikok: a invaded, contactmetamorphic
uralite-diabase (A 583, D); b invaded amphibole-diopside-plagioclase-rock (A 584
D); c dike of quartz-hornblende-diorite in diabase (A 424—D 12509). The alteration
the ophitic texture and the presence of a little, partly uralitized pyroxene
in the latter ropk are probably connected with the neighbourhood of the contact.

4.nbsp;Contact diabase and diorite near Baranca Corra. The samples have been
taken over a distance of about 25 m: ö contactmetamorphic uralite-diabase
(A 551, D); b ditto, invaded (A 552, D); c contactmetamorphic uralite-diabase,
rich in quartz and invaded by dioritic aplite (A 560); amphibole-plagioclase-rock
(A 550, D); e quartz-hornblende-biotite-diorite (A 553—D 12580).

5.nbsp;The Seroe Pretoe, N of Savaneta, consists for a great part of contact-
rocks: contactmetamorphic uralite-gabbrodiabases, amphibole-plagioclase-rocks,
amphibole-diopside-plagioclase-rocks, more or less invaded by dioritic material

6.nbsp;The samples taken from the contactzone NW of Rincon are the following
ones: amphibole-diopside-plagioclase-rocks, with quartz or invaded (A 574, D;

1) Martin (30) p. 53 did not consider the diabase the roof of the bathohth. From his
fieldobservations he concluded, quot;dass der Diabas das Liegende des Diorits ist, welcher
quot;deckenartig sich über die Gehänge der westlichen Kuppen und Hügel ausbreitete und durch
quot;die Verwitterung weit zerfallen ist, so dass er die unterlagernde Formation nur noch unvoll-
quot;ständig verhüllt.quot;

A575, D); invaded amphibolitic rocks (f.i. A576, D); amphibole-plagioclase-
quartz-rocks (f.i. A 571; A 573, D; A 577, D; A 578); quartz-hornblende-biotite-
diorite, a httle altered (A 572—D 12591). The occurrence of aggregates of normal
browngreen hornblende, parallel- and radial-fibrous hornblende, chlorite, ore and
titanite in the latter rock is connected with the close neighbourhood of the
contact.

The amphibolitic rocks merge gradually into the diabasic rocks, and in the
field can be distinguished from the latter only with difficulty. Both are strongly
invaded. The diorite and the contactrocks, however, can be clearly distinguished.
Yet, here and there the dark diorite near the contact merges into the strongly
invaded and hybrid amphibolitic rocks (transition rocks). A small amphibolite
outcrop E of Malmok contains conformable dikes of diorite.

In general, the strikes in the large amphibohte region of NW-Aruba lie
between N80E and NIOOE with locally a dip towards the South. Only a few
strikes N50E, N65E and N165E have been found. The strikes in the region NE
of Santa Lucia and in the surroundings of Andicouri are about N25E, with local
dips towards the East. It must be mentioned that also the hornblende-schists in
these regions have aberrant strikes.

Martin (30) mentioned amphibolitic rocks only from the surroundings of
the Santa Lucia and of Rincon. Similar rocks from NW-Aruba have been con-
sidered by him as finegrained to aphanitic quartzdiorite, quot;als lokale Ausbildung
,,des normalen Quarzdioritsquot; (p. 46). He considers the amphibohtes rocks,
,,welche ohne Schwierigkeit mit den Grünschiefern zusammengefasst werden
,,können,quot; ,,und der archaeischen Schichtenreihe angehörenquot; (p. 56). — J. H.
Kloos (25) considered the amphibohtes a local variety of the diorite, as ,,eine
,,amphibolreiche Ausscheidung im grobkörnigen Quarzdioritquot; (p. 68); and remark-
ed moreover: ,,Möglicherweise müssen die schieferigen Amphibolgesteine auf
,.ältere dioritische Ergüsse zurückgeführt werdenquot; (p. 69).

If we take into consideration the transition of diabase into amphibolitic
rocks and the occurrence of the amphibolitic rocks between the diabase massives
and the diorite batholith, we must come to the conclusion that the amphibolitic
rocks represent the very strongly contactmetamorphic diabases. Possibly, the
diabase tuffs too have been altered locally into amphibohtic rocks, but no rocks
transitional between contactmetamorphic hornblende-schists and the latter
rocks have been found. — The amphibolitic rocks between the Santa Lucia and
Andicouri border westwards on the gabbro massive of the Matividiri, and more
southwards on the diorite. The gabbroic magma of the batholith too must have
metamorphosed the diabasic rocks.

The amphibolitic rocks over large distances show a schisty habit with clear
strikes which do not differ much from the E-W direction. Therefore, they must
have been submitted to the same folding process as that which acted in the diabase-

tuff massive. This process must have taken place during and after the metamor-
phism of these older rocks and, consequently, during the intrusion of the bathohth.
— There are, however, also amphibohtic rocks which do not show a schisty struc-
ture. May be, these rocks came into existence after the process of folding, or they

did not react upon this process no more than did the diabases and little altered
diabases.

Although the diorite and the diabase are rocks different in age and consti-
tution, the intruding batholith and its contact-action upon the country-rock
caused a secondary, gradual transition between both rocks: diabase urahte-
diabase contactmetamorphic uralite-diabase transitionrock between
diabase and amphibolitic rock amphibolitic rock hybrid amphibolitic
rock transitionrock between amphibolitic rock and diorite altered

diorite -gt; diorite. A suchlike transition occurs between the diabase-tuff and the
diorite: tuff httle hornblendized tuff hornblende-schist transition-
rock between hornblende-schist and diorite diorite; or hornblende-schist
contactmetamorphic hornblende-schist amphibolitic rock).

It is remarkable that this contact series does not occur everywhere in the
contactzone. So f.i., the diorite locaUy borders directly on contactmetamorphic
urahte-diabase (see p. 98), whereas in other places different kinds of amphi-
bolitic rocks have developed between these rocks. The dioritic magma can have
caused the alteration of the tuffs into contactmetamorphic hornblende-schists or
borders on invaded hornblende-schists without strong contactmetamorphism.
So, the contactmetamorphism must have been different from place to
place.

Since the amphibolitic rocks must be considered as altered diabases and not
as a marginal texture of the diorite batholith, it is clear that the contactmetamor-
phism in Aruba has chiefly been a process of exomorphism. Endomorphism was
not quite wanting but must have been of a minor importance. As we have seen
the contactzone has the character of a mutual contactzone, in the sense of Lahee
(26), in several places.

The diorite and the amphibolitic rocks have a different texture and structure
but are not so much different in mineralogical composition. This agrees with
the Ideas of N. L. Bowen (7), embodied on pp. 197-201 Effects of magma upon
inclusions of igneous origin). The dioritic magma comes into contact with the
country-rocks and attacks these rocks, according to Bowen quot;reacting with
^^them in such a manner as to convert them into the crystals with which it is
saturatedquot;; consequently, into hornblende and plagioclase. quot;at the same time
precipitating a further amount of this hornblende and plagioclase from its own
substance . In this way the diabasic rocks and the diabase tuffs too must have
been altered into the different described contactrocks; dependent on the distance
from the bathohth, this conversion was greater or smaller. Also quartz and biotite
which occur in several of the contactrocks must have come into existence in
consequence of interaction with the dioritic magma, the latter containing quartz
and mica substance. It must be remarked, however, that in some places of the
contactzone the conversion of the country-rocks into the crystals with which the

dioritic magma is saturated, is not quite carried through; that is to say, in those
rocks which occur very near the diorite and still contain primary pyroxene (see
f.i. the diabases of the contactzone NW of Shete), and in those amphibolitic
rocks with a certain amount of, probably secondary, diopsidic pyroxene. All
these pyroxene-bearing contactrocks border on normal quartz-diorite with horn-
blende and biotite, but without pyroxene. The pyroxene of the amphibohtic
rocks, therefore, cannot be the product of a conversion of the diabase into the
crystals with which the dioritic magma is saturated.

It can be mentioned here, that the contactmetamorphism of the pyroxene-
bearing rocks of the older formation, that of the gabbroid rocks and that of the
pyroxene-hooibergites show the same characteristics as to the conversion of their
pyroxene into the hornblende with which the intruding dioritic magma is
saturated.

Similar contactrocks, as known from Aruba, occur in the Odenwald (Ger-
many) and have been described by Viktor Leinz (27). The amphibohtes of the
southern Odenwald too must have originated from diabases, ,,Schalsteinequot; or
diabase tuffs, although texture relics are wanting. The original rocks must have
been metamorphosed by an intruding diorite. According to Leinz not only the
diabasic rocks have been altered into amphibohte, but also the marginal parts
of the intruding dioritic magma have crystallized into pseudo-amphibohtic rocks
because of the quick cooling and crystallization (see p. 112). Therefore, these
marginal diorites and the true amphibohtic rocks resemble each other very much
and show ,,Konvergenzerscheinungenquot;. As far as we can see, nothing points to
the probabJity that the Aruba diorites did crystallize into amphibolitic rocks;
they do show, however, a little alteration here and there in the contactzone. The
transition rocks on Aruba can all be considered as country-rocks, very strongly
altered and flooded by dioritic magma.

Amphibolitic rocks, occurring as rather big inclusions in the diorite massive:
In several places in the batholith outcrop, especially in the northern parts, we meet small
outcrops of darkcoloured or greeny, schisty rocks with a varying strike. These outcrops are
a few meters long and wide, and must be considered as rocks of the contactzone taken up by
the dioritic magma. Nevertheless, they are a little different from the described amphibolitic
rocks. - A 782—D 13080 (W of Jaburibari), A 783—D 13081 (N of Zumbo), A 784—
D 13082 (W of Turibana), A 785—D 13083 (N of Kudawecha), A 786—D 13084 (Jaburibari)
and A 787 (W of Turibana) are extremely finegrained, parallel- and partly somewhat banded
structured, grano-to nematoblastic rocks. They are chiefly different from the above-described
amphibohtes in their granularity and in the occurrence of several bigger relic-crystals of
hornblende, plagioclase, quartz, and rarely of biotite. These relic-crystals generally do not
lie parallel to the schistosity, and the small crystals curve around them. The hornblende relic-
crystals are the only ones which occur in all of the rocks, whereas the others only occur in
some of them. The relic-hornblendes are non-idiomorphic prisms, partly fibrous or twinned.
The relic-plagioclases are zonal labradors (D^13082). The quartzes are roundish nr eggshaped
grains. D 13084 also contains epidote individuals. A few fibrous biotites and grains of titanite
occur in D 13083; the same rock contains parallel strings of biotite and ore between the

hornblendes. Oblong quartz nests are present in several rocks. It must be mentioned too
that many of the small plagioclase crystals are prismatic, and that several of the small
hornblendes of D 13082 have a darker, brown-green core. Some of the rocks contain narrow
veins of quartz and epidote. - A 430-D 12515 (NE of Seroe Janchi) is a finegrained schistv
malchitic-looking rock with a slightly parallel structure, and with several bigger parallel
stretched, non-idiomorphic hornblendes. Besides, hornblende occurs as small prisms and
grams, partly fibrous. Plagioclase is present as partly zonal laths and prisms of labrador not
quite Idiomorphic with regard to the hornblende (ophitic relic-texture?). Biotite is the serand
dark mineral and occurs as very small plates. Quartz mainly occurs in some roundish and
eggshaped nests. Apatite, some magnetite and titanite are accessory.

Small Exogenous Inclusions in the Diorite: In several places the diorite contains
finegrained, darkcoloured inclusions, roundish, eggshaped or irregularly shaped and of
a size froir about 1 cm. to 10 cm. These inclusions can be easily loosened out of the enclosing
rock or are firmly grown together with the diorite. - A 777-D 13075 (N of Spaansch Lagoen)
is an inclusion of contactmetamorphic uralite-diabase with a narrow diorite-aplitic dike It
IS curious that this rock has not been totally changed into an amphibolitic rock A 770—D
13068 (N of Seroe Pretoe, NW of the Hooiberg) is an invaded hornblende-chlorite-schist
roughly-parallel-structured and with a kind of banded structure. The invasion material is al'
bite-oligoclase with some epidote and apatites. A 771—D 13069 (Seroe Janchi) is a quartz-
hornblende-diorite with a parallel-structured streak of normal amphibolite. The two rocks
do not sharply border on each other. A 772—D 13070 (WNW of the Hooiberg) is an amphi-
bole-plagioclase-quartz-rock with a grano- to diablastic texture and here and there with
plagioclase quot;dropsquot; in the quartz. A 773—D 13071, A 774—D 13072 and A 775—D 13073
found W of the Hooiberg, are dioritized amphibolitic rocks in quartz-diorite. The former are
richer in hornblende and ore and do not contain quartz. They are not sharply bordered on
the diorite and possess an idiomorphic-allotriomorphic-granulose texture A slightly parallel
structure can only be seen in D 13073. Several bigger, non-phenocrystic plagioclaL and
hornblendes occur in D 13072. The composition of the plagioclases varies from oligoclase to
andesine. The inclusions in D 13071 and D 13072, which lie in quartz-hornblende-biotite
diorite, also contain biotite. That in D 13073, in quartz-hornblende-diorite, does not contain
biotite. This mineral occurs in D 13071 as small crystals and as some big, irregularly shaped
crystals which wholly or partly enclose non-idiomorphic plagioclases, hornblendes and more
over apatites, titanite and rutile needles (sagenite texture). For the rest thev consist nf
diorite minerals with normally dioritic properties.nbsp;'nbsp;■ ■ u ot

These exogenous inclusions occur in the whole batholithic outcrop and are obviouslv
small stoped blocks from the contactzone of the batholith roof. Just as the rocks of the
contactzone the inclusions show here and there a more or less strong dioritization The enrlo
sing diorites in D 13069 and D 13071 show contact alteration. Tlteir hornblende occurs t
aggregates o small crystals. In the former rock quartz occurs abundant in and between the
crystals of these aggregates.

Appendix: A 22-D 13085 (Seroe Gerard) is a hornblende-biotite-granodiorite with a
darkcoloured segregation, roundish and not sharply bordered. The diorite and the segregation
consist of the same minerals and their crystals work in with and between each other -
The segregation consists mainly of very Hg microperthite individuals (undulose), between
which some less big quarts individuals undulose) occur, the latter allotriomo pluc with
egard to the potashfeldspar. These crystals contain as oikocrysts a great many smL chada-
crysts 1) very small and bigger plagioclase prisms, zonal and of an average cLposition; 2)
hornblende pnsms, co umns and needles; 3) biotites, several of which hate been totally o
partly altered into chlorite, titanite and epidote; many of the biotites enclose verv sLll
plagioclase pnsms; 4 magnetite; 5) apatites. Locally, the chadacrysts lie very close together,
so that the oikocrysts cannot be distinguished as such, but still occur between them

The hmestone is found on Aruba mainly as normal limestone and less as
phosphorite-limestone.

The surface of the normal limestone is hard and then shows a quot;Lapiesquot; or
quot;Karrenquot; habit, or the rock has a more grainy and softly tuffoid character. The
rock has been weathered here and there into a reddishbrown substance, or is
covered by limestone fragments and blocks.

At the basis of the limestone beds the rock is strongly conglomeratic and
contains fragments (pebbles) and minerals of the underlying older rocks, that is
to say, of diorite, diabase, schists, tuffs, and so on. In the upper parts of the
limestone covering only the minerals of the older rocks, chiefly the diorite quartzes,
can be found. In some places, where the limestone is hardly or no longer present,
a covering with pebbles can still be seen; f.i. here and there in the northern regions
of the older formation (diabase and porphyrite pebbles) and on the diorite N of
Sabana Lodo (aplite pebbles).

Although the limestone occurs in a varying way, the samples can be described
together because of the similar composition. The rock is splintery or granular,
rarely crystalline, partly porous. The colour varies from white and gray to pink-
ish, cream- and beige-coloured, yellowish and brownish. Except the limestones
found near the uppercourse of Rooi Hundoe, the rocks contain sharply angular,
less roundish, quartz fragments in a greater or smaller amount, here and there
in a very small amount. Moreover, several rocks also contain some plagioclases,
partly chloritized or limonitized hornblendes, pyroxenes, biotites, ore and epidote.
Many of the rocks are Lithothamnia limestones. For the rest, their fossil-content
is rather varying. The following organisms have been found: Amphistegina,
Operculina, Rotalidae, Miliohdae, Textularidae, Globigerinae, Lamellibranchiata,
Gastropoda, Hexacoralla, Echinoidea, Algae. Especially the limestones at the
uppercourse of Rooi Hundoe, at Sabana Lodo, .and near Seroe Blanco (SE)
contain many remnants of, partly quot;big-belliedquot;, Amphistegina.

See also the considerations by Martin (30) on the quot;Aeltere quartäre Korallenkalkequot;
(p. 79), quot;Phosphoritequot; (p 88), quot;Jungquartäre Bildungenquot; (p. 125).

The list contains the Mollusks sampled by us (1930) and by I. Boldingh \1909—
1910). The specimens have been classified with the kind help of Dr. C. G. T. H. Bayer,
custodian of the Rijksmuseum voor Natuurlijke Historie te Leiden (Holland). They have
been determined through comparison with the recent Mollusks kept in the mentioned
museum, and with the material of Martin in the Geologisch-Mineralogisch Museum te
Leiden (described by J. LoRiii (29); see also the list of determinations by Schepman in
Martin's book, pp. 125—127, M. M. SChepman (41), L. M. R. Rutten (38)). - New species
do not occur in the list.

Avca deshayesii Hanley - lower terrace SE of Oranjestad; Salinj a NW of Oraniestad-
left bank of Rooi Taki.

Area aff. zebra (Swainson) - lower terrace SE of Oranjestad. The specimen differs from
A. zebra in having less strongly developed big ribs, between which about three narrow
ribs occur; the central rib of these three ones is the stronger one.
Isocardia - left bank of Rooi Taki. Internal cast.

Lucina tigerina L. - lower terrace SE of Oranjestad. The specimen is aberrant in having a

relatively high hinge, and a curved lower part of the posterior border of the ligamental
groove.

ICardiiim muricatum L. - left bank of Rooi Taki. The specimen may be too flat to belong
to the genus Cardium.

ICardium {Laevicardium) serratum L. - Salinja Druif. Lorié determined similar specimens
as C. laevigatum (Lam.)

Tellina ?cf fausta Donovan - Seroe Colorado phosphate. Internal casts. The palliai line is
a little aberrant, but still lies within the range of variation of T. fausta

Pecten [Chlamys) [Plagioctenium) concinnatus Woodr. 1925 - left bank of Rooi Taki- E
of Oranjestad; Boegoeroei. The specimens show concentric lamellae also on the lower
part of the ribs. In the description by W. P. Woodring (quot;Mioc. mollusks from
Bowden, Jamaicaquot; - Contr. to the Geol. and Pal. of the W.I., Publ of the Cam
Inst, of Wash. 366-1925, p. 70) the specimen (a left valve) lacks the mentioned
lamellae, although the figure shows them clearly on the lower part of the ribs - The
right valve (not known to Woodr.) is a little more inflated than the left one.

Isophyllastrea rigida (Dana). - Ree. Although the specimen is somewhat rounded-off the
toothed septal margins still can be clearly distinguished. Calice 7—11 (15?) „im
(properly speaking 7-24 mm). Septa 10—14 (15?) per cm. Septa in calice 29—
50. More or less hemispherical (diameter 7 mm, height 4 mm). Corallites generally
polygonal.nbsp;^

Antiguastrea cellulosa (Duncan) Vaughan. - Seroe Colorado. Vaughan 1901 determined the
specimen, sampled by Martin, as Orbicella tenuis (Duncan). According to Vaughan this
species points to Ohgocene. Since both Martin and Boldingh sampled this species in
the Seroe Colorado phosphate, it is very probable that the fossils occur here in situ and

that they are no derived fossils. If the sp. is really Oligocene, part of the Seroe Colorado
limestone must be Tertiary, i)
Colpophyllia nutans (Müller).
Agaricia agaricites (L.).
Siderastrea siderea (E. and S.).

Pocillopora of. guantanamensis Vaugh. 1919. - Near Dos Playa. According to Vaughan (1919
p. 343 and p. 344) this sp. is of the age of the Antiguan Oligocene (Cuba). The Aruba
specimens, however, occur in the lower terrace, which consists of quaternary limestone.
Stylophora sp. - Seroe Blanco (NE of Oranjestad). According to Vaughan (1919 p. 334) the
stratigraphie range of the genus in America is from the upper Eocene to Miocene. The
Seroe Blanco limestone, however, is very probably of a quaternary age. The calices of
the Aruba specimen are maximum 1 mm, mostly mm. The distances between the
calices are maximum about V4 mm, mostly very small, 6 Septa. Here and there hardly
an indication of a second cycle.
Stephanocoenia inter septa (Esper).
Dichocoenia sp.
Acropora muricata (L.).
Acropora palniata (Lam.).
Porites astreoides Lam.
Pontes pontes (Pallas).

Agassizia coriradi {Hemiaster Bouvé 1851). - Left bank of Rooi Taki. in the West-Indies

this species is only known from the Eocene.
Clypeaster antillanim Cotteau 1875. - Left bank of Rooi Taki. This species is known from
Eocene, Oligocene and Miocene (also recent?).

As to the Molhisks Martin, Lorié and Schepman accept a quaternary age
for the Aruba specimens: 48 species. Pecten concinnatusis the only fossil Mollusk
which is miocene (Bowden, Jamaica), as far as is known. It occurs in the left
bank of Rooi Taki, in the beds of Boegoeroei and in the terrace E of Oranjestad,
probably in quaternary lime.stones. The two Echini are eocene to oligo-miocene, as
far as is known, and occur in the beds of the left bank of Rooi Taki, as well as the
Pmiocene Pecten concinnatiis. These beds contain quaternary fossils (Mollusks)
as well. —.Most of the corals of Aruba are c^uaternary or even recent: 16 .species.
(Among th(^se species also Favia jraguni Esper. anà Maeandra strigosa (Dana),
sampled by Martin, are reckoned). Antiguastrea celliilosa from the Seroe Colorado
may be oligocene. Goniopora regidaris (Duncan) Vaughan 1919 (= Alveopom
regtdaris Duncan, in Vaughan 1901), from the Seroe Colorado and sampled
by Martin is oligocene too, according to Vaughan. Pocillopora cf. guantana-
mensis may be Antiguan oligocene. Siylophora sp. may be eocene to miocene.
The two latter species, however, occur in the lower terrace limestone, which
is quaternary, all but certailnly.

These fossils and the absence of Orbitoid Foraminifera make it obvious that
at least by far the greatest part of the hmestone is of a Quarternary age. However,
Tertiary formations are not entirely wanting on Aruba, in view of the fossils. One

Other corals and also mollusks occurring in the Seroe Colorado limestone and phos-
phate are, however, of quaternary age.

sample (D 13254), froiii Butucoe (see the map quot;Tquot;), must be certainly Older or
Middle Tertiary. This limestone is a beige-coloured, somewhat splintery limestone
without quartz fragments or other minerals. It contains, beside Globigerinae,
Textularidae, Miliolidae, Lamellibranchiata and Lithothamnia two species of
Lepidocyclma. Hence, this rock can be Upper Eocene to Lower Miocene.

Phosphatized limestones occur mainly in the SE-corner of Aruba: Culebra,
Seroe Colorado. Near Butucoe, near Pedro Mosa and elsewhere small phosphate
spots occur among the normal limestone. The phosphates look breccious; thev
may contain a certain amount of calcite and grains of quartz. Organisms cannot
be recognized except corals. The rocks 3206—D 2262 to 3210-1) 2267 (Delft
collection) and P 209—D 6563 from the Culebra show the phosphate sharply
bordered on and as rounded-off fragments in white or brownish limestone. The
phosphates are conglomeratic where they lie just above the older rocks
(diorite).

The limestone lies unconformably on the two older rockformations which
must have been denuded for a great part already before the deposition of tliis
younger formation. Since in almost all of the examined limestone samples - taken
from places a few dm. to more than 10m. above the older rocks - quartz occurs
as acute-angular, rarely as rounded-off fragments, we can accept all but for
certain that only part of the island was under sealevel during the deposition of
the Ouarternary limestone. Such quartz fragments have been found in the lime-
stone of the higlier situated and dipping beds as well as in the rocks of the surround-
ing low terrace. It must be mentioned that the Tertiary limestone from Butucoe
does not contain quartz fragments. May be, the Tertiary sea covered the whole

The limestone covering lias been partly denuded and today it is found
especially in the Southeastern part, further as a zone, about 2km wide, along the
S- and W-coast, and as a narrow, frequently interrupted border along the N'-coast.
Only in a few places the limestone occurs as isolated and small coverings on the
older rocks, f.i. those in NW-Aruba, Seroe Pela, Seroe Plat, near Andicouri,
near Dos Playa.

If we accept that already during the deposition of the younger limestone the
NE to E tradewinds existed, it is evident that the varying development of these
younger limestones along the S- and W-coast and along the N^ and NE-coast
may be sought in the different conditions on these« coasts.

The higher situated limestone beds have a thicknessM'hich varies from Im. to
more than 15m.; they show a varying strike and dip:

On the inner side (land side) of the wide zone along the SW- and S-coast, from Ponton
o Seroe Colorado: N 90 E to N 140 E with dips towards the S and SW; the latter are on the
whole slight, but vary from 0° to about 40°. - Exceptions: San Barbola N 60 E, 25 S; a
small outcrop W^ of Seroe Bientoe, near Plantersrust, N 60 E, 30 N and N 120 E, 30 S (double
plunging anticHne?); part of the Culebra (SE-Ar) with eastward dipping beds,'

The large limestone plateau between Seroe Blanco, Fontein and Baranca Corra is about
horizontal; the part N of Seroe Blanco may dip slightly eastward.

The small higher limestone plateaus in NW-Aruba about horizontal or slightly dipping
eastward.

The younger and lower limestone terrace, the thickness of which varies from
Im. to more than 15m., and the altitude of which on the coast varies to max.
10m. (Nanki, near St. Nicolaas, see topographic map), shows a varying width and
its surface lies about horizontal or dips very slightly towards the neighbouring sea.
There are the following particularities. A slight quot;anticlinequot; with an E—W axis
occurs just W of Noordkaap. — S of Rincon the terrace occurs as two terraces
(elevated beaches), separated by an escarpment which lies between the 5m and
10m contour Hne; more southwards this escarpment is absent and there the lower
terrace dips slowly towards the E.—N of the Seroe Grandi (N-Ar.) two levels,
separated by an escarpment or a steep slope, can be found lower than the 5m.
contour.

The higher situated limestones (altitude 10m. to about 135m.) are bordered
by the lower terrace limestone on the seaside (altitude to about 10m., maximum
to 20 m.). In many places the higher and the lower limestone merge or seem to
merge gradually. In the surroundings of Fontein and Rincon the higher and lower
terrace are sharply separated by a vertical escarpment. This escarpment hes
on the 20m. contour line or there abouts and is also present in some places along
the S-coast (see the topographic map).

Comparing the dips of the higher situated beds we must come to the con-
clusion that, before the denudation, the Hmestone must have been present as a
slightly arched cap over a great part of the island. The culmination of this brachy-
antichne lies nowadays along the NE-coast. Very probably the dips of this anticline
are no primary dips and are due to slight orogenic movements. A result of these
orogenic movements may be also a hmestone troughfault of 10m. wide, 100m.
long, in the direction N 100 E, on the plateau of Baranca Kasioenti.

The phosphorites on the Seroe Culebra and the Seroe Colorado are altered,
higher situated limestones. The phosphatization has occurred after and during
the deposition of excrements of seabirds (guano); see Martin (30) p. 93. It is
curious that just E of the top of the Culebra, in an old phosphate working, the
phosphate beds dip towards the E and are covered by organic limestone with
Serpulae (P 209—D 6563) which contains at its basis rounded-off fragments of
the phosphorite; the thickness of this bed is 1—-2m (This profile was already known
to Ir. G. Duyfjes; see also Martin (30, p. 94)). Consequently, after the phos-
phatization different changes in level must have taken place.

Very young limestone deposits occur f.i. in Rooi Prins (with fragments of
hornblende-schists, diabase and quartz), in the Boca W of Noordkaap (cemented

the quot;rooiquot; S of Seroe Largo a rock occurs which is very probably a quot;rooiquot; deposit
with a limestone cement (N 60 E, slightly dipping towards the S.).

Before and about parallel to the S-coast a long, frequently interrupted
shore-coralreef rises for the greater part above sealevel. As we can see on the map
the lagoon has a varying width and here and there the reef meets the coast. The
reef hes on the seaside of a plain of abrasion, and has been partly brought above
sealevel by a subrecent descent of the sealevel (see the chapter geological history).
— It is clear, that in consequence of the tradewinds and a rapidly increasing
depth a coralreef could not grow along the E- and NE-coast. In front of the W-
coast only separate coralstocks are met with. The growth of a reef may have been
prevented here on account of the strongly sandy character of the covering of the
plain of abrasion. — The very low peninsula of Taratata probably must be reckoned
too among this very young reef-formation. Between Punta Braboe and Oranjestad,
just NE of the lagoon, an abrasion escarpment, 1,5—2m high, separates the lower
terrace — which has an altitude of less than 5m here — and the abrasion plain
upon which the reef came into being. Along the S-coast similar escarpments occur
here and there.

Especially along the S- and W-coast large deposits of detritus occur, mainly
of diorite detritus (sandy detritus). These deposits are typical quot;rooiquot; deposits and
originated from the hills in the central parts of Aruba. The detritus hes on the
younger terrace limestone or on the older rocks. In many places the younger
limestone must have been removed and replaced by detritus. In some spots the
limestone lies on diorite detritus, which must be older; the upper part of this
detritus has been cemented by limestone. Here and there along the S-coast the
detritus occurs as a delta-formation. quot;Rooienquot; occur in the deposits to a few
meters deep. Two areas of diorite detritus SE of the Hooiberg, which he in the
midst of diorite and which are some meters thick, have probably been deposited
during a period in which the base-level of erosion of the island was a little higher;
these deposits have been dissected by the present quot;rooienquot;. In some places the
detritus is in the depth a hard, loamy rock, rich in sand and small gravel frag-
ments 1). - (plate I, fig. 2).

The coastdunes, partially composed of limestone-sand, partially of quartz-
sand (depending on the place of occurrence) occur on the E-, NE-, N- and W-coast.
They lie on the detritus deposits or on the terrace limestone. South of Rincon they
partly cover the three terraces. — On the terrace along the N-coast we find here
and there heaps of limestone and coral fragments, thrown up by the waves.

Small peat deposits were found in the subsoil of the quot;rooiquot;-mouth just SE of
Oranjestad, during the foundation working of a bridge. It seems that they also
occur in the quot;rooiquot; just SE of the Canashito(?).

As in Curacao (f.i. Schottegat) some handshaped inlandbays with a junction-
canal to the sea occur on Aruba on the S-, W- and N-coast. in distinction from
the Schottegat they are entirely dry, except the Spaansch Lagoen junctioncanal.
As to their genesis, see G. J. H. Molengraaff (31, pp. 8—12), and Martin (30
pp. 119—124).

The E-, NE- and N-coast show many undercuts, wavecut chasms and coves
in the rocks, the socalled quot;boca'squot;, which owe their existence to the tradewinds.

1) Martin near Santa Cruz sampled finegrained, lightgrayish to yellowish sandstones
with only very little cement. He described them briefly on p. 60 (30) as quot;Geschiebequot; in the
chapter quot;Kreide formation?quot;. This rock proved to be cemented diorite-quartz detritus,
psammitic, porous and with a slightly stratified structure. The cement is brownish and
siliceous with here and there accumulated muscovites. The allogenic constituents are by
far the greatest part acute-angular, less rounded-off, diorite-quartzes. Also a few muscovites,
hornblende grains, microclines, tourmalines and ore grains are present

In distinction herewith the S- and W-coast show large deposits of detritus and a
gentle course of the young shoreline. — Where no older rocks form the coast and
no terrace coast exists, a sandy beach can be found.

In the large diorite plain of W-Aruba many typical coves occur in the big
diorite blocks (plate I, fig. 3). These coves must have been formed during a trans-
gression period. They occur to an altitude of about 70m. and have their openings
almost exclusively on the W-, SW- and S- side of the monoliths. A very few coves
have their opening on the NW- or N-side; a single one has been found on the
SSE-side of a block i). The same transgression caused the forming of coves in
the higher situated limestones. These can be very well seen f. i. in the escarp-
ment near and SE of Fontein (20m. contour line). The large caves in these
higher limestones are for the greater part the result of quot;Karstquot; phenomena
(sinter deposits). The bottom of many of these caves is covered with excreta of
bats. — See also Martin( 30, p. 106) quot;Erosion durch das Meerquot;.

1) In connection with the distribution of these diorite coves Martin indicated in his
map the quot;alte Meeresbuchtquot; (see also Martin p. 48). In view of the small number of obser-
vations by Martin and of the only partial exactness of his map, this line indicating the quot;alte
Meeresbuchtquot; is only right to a certain extent.

In the nineteenth and in the beginning of the twentieth century Aruba ex-
ported some gold. The latter was won partly from the many goldbearing quartz-
dikes in the batholith and in the older formation, especially in central, NE- and
N-Aruba, and partly from the placers (alluvial detritus deposits). Since about
1914 the exploitation has been stopped. Also the phosphateworking in Seroe
Colorado came to an end. Traces of this gold and phosphate mining can be found
in several places of the island (see also the topographic map). For further details
concerning the occurrence, the mining in the course of years and the economy of
these two minerals, see the older literature of Aruba (f.i. Martin (30) pp. 60—67
and pp. 88—101).

Instead of the gold- and phosphateworking other exploitations have been
started, a short time ago. They are the mining of quartz for highway construction
(the quartz was used in the foundation of the new road between Oranjestad and
Sint Nicolaas) and the digging away of socalled quot;fresh sandquot; (diorite sand) for
the fabrication of concrete and cement (C. P. I. M.). These exploitations too have
been put an end to after the quart/, and the quot;fresh sandquot; were no more in demand.

The oldest rocks known in Aruba are very probably of a Cretaceous age. They
are volcanic products, partly deposited in a shallow sea. Probably in that time
Curasao and Aruba must have formed one country, for diabase pebbles on Aruba
very much resemble the diabase rocks of Cura9ao. At the end of the Mesozoic
time or at the beginning of the Tertiary period this volcanic rockseries was folded
in the depth i) (E-W strikes) and at the same time intruded and metamorphosed
by a diorite bathoHth magma with its various differentiates. After that, a strong
denudation i) must have taken place, which removed the greater part of the batho-
lith roof and the highest parts of the batholith itself. — Tertiary limestone has
been found only in one place with certainty. Its age could not be exactly deter-
mined and lies between Upper Eocene and Lower Miocene. - As far as we can see,
by far the greatest part of the Aruba limestone is Quaternary. Except during
the deposition of the mentioned Tertiary limestone Aruba must have been above
sealevel in Tertiary time and must have been subdued to denudation; at all
events, no other Tertiary rocks have been found (only some possibly Tertiary
fossils). In older Quarternary time a positive change in level, by which the
greater part of the island came under sealevel, caused the deposition of limestone
upon the denuded and abraded older rocks and partly upon their detritus. After
that, a slight, ?asymmetrical upwarping of the limestone beds must have taken
place, for the higher situated limestones occur today as a slightly arched cap with
a pitching axis about NW-SE (main axis of Aruba), partly removed. In conse-
quence of this upwarping and a negative change in level (probably in connection
with the beginning of the Glacial Period)'the older rocks and the hmestone in-the
central parts have been eroded, and their detritus has been partly deposited upon
the plain of abrasion which has been formed at the same time at the border of the
island. The positive change in level after the Glacial Period may have caused
the deposition of younger limestone on the plain of abrasion, the forming of coves
in the older limestone and also of the coves in the big diorite blocks. The latter
coves occur today to about an altitude of 70m, and have their opening in general
on the W- and SW-side of the blocks. So. the higher parts of the island have not
been under sealevel during that time. An upheaval of the island followed on this

1) Probably, younger Cretaceous rocks (compare with Cura9ao) have been present
above the volcanic series, but have been removed without .leaving traces. Only one, rounded-
off, Cretaceous Ammonite, found in the Quaternary Seroe Colorado phosphate, may
have originated from younger Cretaceous beds which occurred on or in the close neighbour-
hood of Aruba (see Martin (30, p. 60); this fossil very much xesemblesAmrnonites Treffry anus
Karst., known from Cretaceous beds near Bogota).

transgression. A plain of abrasion was formed on the younger limestone (still
present today), together with the escarpment in the older limestones (today on the
20m. contour hne). A second and very small upheaval caused the genesis of a
second plain of abrasion in the younger limestone here and there (f.i. S of Rincon)
separated from the former by an escarpment and a little lower. On the seaside of
a submarme plain of detritus or of a plain of abrasion fin the latter case another
pai^r of changes in level must be accepted) along the SW-coast, a coralreef grew
and persisted (shore-coralreef along the SW-coast). The subrecent descent of the
sealevel of some meters (5-6m.; R. A. Daly (13) p. 174) brought the younger
limestone and also this coralreef above the sealevel for a great part i). The recent
denudation of the island began, and big masses of detritus, especially of diorite
detritus, were deposited on the terrace limestone and in the lagoon. Dunes came
uito being along the W-, N- and E-coast, quot;boca'squot; along the N- and E-coast The
handshaped inlandbays with a junctioncanal to the .sea, which are a quot;rooiquot;-
•system and which are almost (Spaansch Lagoen) or quite dry (f.i. Druif, N-Aruba)
may have been formed already during the Glacial Period. The two areas of
diorite detritus SE of the Hooiberg, which lie in the midst of diorite, have originated
from a time before the subrecent descent of the sealevel, when Aruba had a higher
base-level of erosion; today these detritus deposits are dissected by the quot;rooienquot;
— The valleys in the older formation contain here and there very young limestone
just as the quot;boca'squot;. The rare peat deposits also must be very young.

It must be remarked that the younger history of Aruba and the occurrence
of the limestones agree very much with those of Curagao (see G. J. H xMolen-
graaff (31, pp. 6—12), and (32, pp. 683-687)). Molengraaff called the older
hmestone Pleistocene and the younger limestone Holocene.

1) The given history of the younger movements is the most simple one. It goes without
saying that the geological data can be interpreted in a more complicated way too, in accept-
ing more changes in level.

As far as we can see, the occurrence of the relevant terraces does not plead against their
genesis m consequence of an upheaval or descent of the island. Indeed, the occurrence of the
terraces is defined mainly by the mentioned subrecent descent of the sealevel, and by the
following erosion. The upheaval and descent of the island must have occurred in a somewhat
vertical direction.nbsp;lt;

CORRELATION OFTHE TWO OLDER FORMATIONS ON ARUBA
WITH THOSE ON OTHER ANTILLEAN ISLANDS^).

Aruba lies tectonically much higher than Curasao and Bonaire because of
the Iiigher upwarping of the xMesozoic rocks, and therefore shows a much deeper
denudation 2). In this way it can be understood that today only the deeper parts
of the Cretaceous formation are still present on Aruba, and that a very big part of
the quartzdiorite batholith crops out there. Rocks, however, older than Cretaceous
and lying under the diabases and tuffs, do not crop out, as far as we know.

Diabase-Diabasetuff formation: This formation can be compared with the
diabase formation and the lower beds of the Knip formation on Cura9ao (Molen-
graaff (31)). The great resemblance between some of the Aruba and the Cura9ao
diabases, and the occurrence of a conglomerate with Curacao diabase-pebbles
on Aruba point to similarity. — The older formation can also be compared with
the lower parts of the Washikemba formation on Bonaire, in which diabases and
diabase-tuffs predominate. The diabases on the two islands resemble each other
more or less (Kloos (25), Pijpers (34)). — As far as we know, diabasic rocks do
not occur on the Venezuelan islands between Bonaire and Trinidad. The amphi-
bolite, the different kinds of green schists with hornblende, epidote, chlorite and
albite, and the metamorphosed porphyrites on Orchila (see L. Rutten (39) pp.
1106—1108) may be compared with the strongly contactmetamorphic and dyna-
mometamorphic rocks in the older formation of Aruba. — Although only the
lower parts of the older formation on Aruba have been preserved, this formation
as a whole must be the same as the late-Cretaceous volcanic series in the West-
Indian islands .?Cuba, Haiti, San Domingo, Jamaica, Porto Rico, the Virgin
Islands, St. Croix, St. Barts, St. Martin, PAnguilla, ?St. Kitts, Antigua — W
sievers (42) mentions the occurrence of diabase on the peninsula of Paraguana,
the part of Venezuela which lies nearest Aruba.

Quartzdiorite batholith with differentiates: Rocks similar to the batholithic
and dike-rocks on Aruba occur in NW-, central and E-Curafao, but do not take
up much room there (Molengraaff (31, pp. 49, 57-58), Vermunt-M Rutten
(50), Pijpers (35)). In Bonaire the bathohth must lie still deeper than in Cura9ao
Only one outcrop of a porphyritic quartz-hornblende-diorite dike has been
found in the diabase near Seroe Grita Kabai (Pijpers (34)). - In many of the

60-61) and L Rutten (39, p. 1105). Concerning a comparison between the three Dutch
Leeward Antilles and the adjacent regions, see L. Rutten (40 pp 439—440)

J) In this connection it is worth to mention that Aruba lies nearest the South American
continent.

islands between Bonaire and Trinidad rocks occur which are comparable with
the plutonic and dike-rocks of Aruba, being of about the same constitution and
Page. These islands are El Roque, POrchila, Blanquilla, Los Hermanos Los

Testigos (L. Rutten (39)). —Intrusions of youngest mesozoic or eocene quartz-
diorite in mesozoic rocks, folded in the same time, occur in Mexico, PJamaica
Cuba, PHaiti, PSanto Domingo, Porto Rico, the Virgin Islands, St. Croix, St.
Martin, PSt. Barts. — About the occurrence of igneous rocks in NW-Venezuela
consanguineous with the intrusive rocks on Aruba or not, and of about the same
age or not, see L. Rutten (39, pp. 1108-1110). As to a general view concerning
the Igneous rocks of the Western Cordillera of South America, see f i Iddings
(22, pp. 489—491).

Since the underground of Aruba consists by far the greatest part of igneous
rocks, rather deeply weathered, that is to say of diabasic and dioritic rocks, it
is clear that this underground must act as a rather good water reservoir.

The hilly older formation, poor in vegetation, is not suitable for the purpose
of winning water, except in the lower course and the mouth of the big quot;rooienquot;,
f.i. of Rooi Prins. The quot;rooienquot; with a bed of metamorphic tuffrocks — the latter
may be looked upon as not permeable for water — might receive consideration
in view to a contingent damming up, f.i. the mentioned Rooi Prins. — The spring
of Fontein occurs on the boundary (plain of abrasion) between the limestone cover-
ing and the underlying older formation. The plain of abrasion of the older
formation must dip slightly to the N here.

The detritus of the batholithic outcrop, and - to a certain extent - also the
limestone prevent much rainwater from flowing off, and retain it. Since the
higher diorite hills lie along the N- and NE-coast, and the large and flat
detritus plains and limestone areas lie on the S- and W-side of the island, water
may be won best in W- and S-Aruba. The wells can be made in the lower
limestone terrace along the W- and S-coast as well, the limestone covering here
being only a few meters thick and overlying diorite and detritus. Still, as some
wells prove, water can also be won in the higher diorite hills — Since the land-
scape is very flat in the mentioned S- and W-parts of the island, it will be difficult
to dam up the quot;rooienquot; here. Such damming up will effect inundation over large
areas in times of strong rainfall.

It must be remarked that already many wells have been constructed in the
mentioned regions suitable for the purpose of water-winning. For the greater
part they contain fresh or almost fresh water.

About the geohydrology see further: Martin (30, pp. 113—118); Molen-
graaff (31, deel 2, p. 97); Ir. G. Duyfjes (17).

1) Martin remarks on p. 118, quot;dass das Östliche Kalkplateau für die Wasserfrage
quot;bedeutungslos ist, da die Schichten sich hier in schwebender Lage als Hangendes der Felsen-
quot;meere von Diorit und nur in geringer Höhe über dem Meeresspiegel befinden,quot;

1.nbsp;Anonymus. quot;Mijnbouwkundige en Geologische onderzoekingen.in de kolonie Curaçaoquot;
- Tijdschr. Kon. Nederl. Aardr. Genootsch. 1910, 27, pp. 1239—1241.

2.nbsp;Anonymus. quot;Phosphaatquot; - Encycl. voor West-Indië, 1914—1917, pp. 558—561.

3.nbsp;Asklund, B. quot;Petrological Studies in the neighbourhood of Stavsjö at Kolmardenquot; -
Sveriges Geologiska Undersökning Ârsbok 17, 1923.

4.nbsp;Becke, F. quot;Ueber Quarzfremdlinge in Lamprophyrenquot; - Tschermak's Mineralogische
und Petrographische Mitth., Band 11, 1890.

5.nbsp;Benthem Juttink, Tera van quot;Marine Molluscs of the island of Curaçaoquot; - Bijdragen
tot de Dierkunde, uitg. Zoöl. Gen. Natura Artis Magistra, Amsterdam, 25, 1927, pp.
1—36.

8.nbsp;Burrington Baker, H. quot;Land and freshwater molluscs of the Dutch Leeward Is-
landsquot; - Univ. of Michigan. Occasional papers of the museum of zoology 21. 1924.

10.nbsp;Cloos, H. quot;Das Batholithenproblemquot; - Fortschritte der Geologie und Palaeontologie.
Heft 1, Berlin 1923.

11.nbsp;Colony, R. J. quot;The final consolidation phenomena in the crystallization of igneous
rockquot; - Journ. of Geol. vol. 31, no. 3, 1923, p. 170.

14.nbsp;Duyfjes, G. quot;De mijnen van Arubaquot; - Neerlandia 15, 1911, pp. 277—280.

15.nbsp;Duyfjes, G. quot;Het landschap van Arubaquot; - Neerlandia 15, 1911, pp. 272—274.

16.nbsp;Duyfjes, G. quot;Goudindustriequot; - Encycl. voor West Indie, 1914—1917, pp. 318—320.

17.nbsp;Duyfjes, G. quot;De watervoorziening van de Benedenwindsche Eilanden van de kolonie
Curaçaoquot; - De Ingenieur 1914, no. 12.

20.nbsp;Hobbs, W. H. quot;The unstable middle section of the Island Arcsquot; - Verhandel. Geol.
Mijnb. Genootschap voor Nederland en koloniën, Geol. Serie, deel 8, pp. 219—262, Juli
1925 (Gedenkboek Verbeek).

24.nbsp;Jesurun, A. quot;De phosphaten van Aruba en Klein-Curaçaoquot; - Neerlandia 15, 1911, pp.
282—285.

25.nbsp;Kloos, J. H. quot;Untersuchungen über Gesteine und Mineralien aus West-Indienquot; -
Samml. des Geol. Reichsmuseums in Leiden, Ute Serie, Beitr. z. Geol. v. Niederl. West
Indien u. angrenzender Gebiete, Band I-Heft 1. 1887—1889.

27.nbsp;Leinz, V. quot;Die Amphibohte des südlichen Odenwaldes und ihre Beziehungen zu Dioriten
und Granitenquot; -Tschermaks Mineralogische und Petrographische Mitteilungen, Band
42, Heft 2, 1931 - pp. 82—134.

29.nbsp;LoRié, J. quot;Fossile Mollusken von Cura9ao, Aruba und der Küste von Venezuelaquot;
Samml. Geol. Reichsmuseums in Leiden, Ute Serie, Beitr. z, Geol. v. Niederl West
Indien u. angrenzender Gebiete, Band I — Heft 1, 1887_1889.

30.nbsp;Martin, K. Bericht über eine Reise nach Niederländisch West Indien und darauf
gegründete Studien, 2, Geologie, 1888, Leiden.

31.nbsp;Molengraaff, G. J. H. Geologie en Geohydrologie van het eiland Curagao 1929 —
Delft.

32.nbsp;Molengraaff, G. J. H. quot;Curagaoquot; - Leidsche Geol. Mededeelingen deel 5, 1931,
(Feestbundel Prof. Martin).

33.nbsp;Oort, E. D. van quot;Ueber einen Sirenenwirbel aus dem Serro Colorado auf Arubaquot; -
Samml. Geol. Reichsmuseums Leiden, Ute Serie, Beitr. z. Geol. v. Niederl. West
Indien etc.. Band II — Heft 2, pp. 164—168, 1902.

34.nbsp;Pijpers, P. J. Geology and Palaeontology of Bonaire - Diss, in press (Geographische en
Geologische Mededeelingen. Publicaties uit het Geographisch en uit het Mineral-Geol.
Institüut der Rijksuniversiteit te Utrecht. Physiographisch-Geologische Reeks no. 8).

35.nbsp;Pijpers, P. J. quot;Some Remarks on the Geology of the Surroundings of quot;Ronde
Klipquot; (East Curafoa)quot; Proc. Kon. Ac. v. Wetensch. te Amsterdam 34 no 7 1931
pp. 1023—1027.

36.nbsp;Rosenbusch, H. Mikroskopische Physiographic der Massigen Gesteine. Erste Hälfte:
Tiefengesteine und Ganggesteine - 1907.

38.nbsp;Rutten, L. quot;Our palaeontological knowledge of the Netherlands West Indies in 1930quot;

-nbsp;Leidsche Geologische Mededeelingen, deel 5, 1931 (Feestbundel Prof. Martin).

39.nbsp;Rutten, L. quot;On rocks from the Venezuelan islands between Bonaire and Trinidad
and on some rocks from Northwestern Venezuelaquot; - Proc. Kon. Acad. v. Wetenschappen
te Amsterdam, vol. 34, no. 8, 1931.

40.nbsp;Rutten, L. quot;De geologische geschiedenis der drie Nederl. Benedenwindsche Eilandenquot;

41.nbsp;Schepman, M. M. quot;Molluscaquot; - Encyclop. van West-Indië, 1914_1918, pp. 477_482

42.nbsp;Sievers, W. quot;Richard Ludwig's Reisen auf Paraguanaquot; - Globus 73 1898 pp 303—
309.

44.nbsp;Stelzner, A. quot;Ueber Kalkstein und Kalkphosphate von Curaçaoquot; - Neues Jahrbuch
1877, pp. 415—416.

45.nbsp;SuEsz, E. Das Antlitz der Erde, 1908-1909 (and French translation La face de la
Terre, 1913.),

46.nbsp;Vaughan, T. W. quot;Some fossil corals from the elevated reefs of Curagao, Aruba and
Bonairequot; - Samml. Geol. Reichsmus. Leiden, lite Serie, Beitr. z. Geol). v. Niederl.
West Indien u. angr. Gebiete, Band II —• Heft 1, pp 1_91 1901

47.nbsp;Vaughan, T. W. quot;Résumé of the present status of geologic correlation of the Creta-
ceous and Tertiary formations of the Antillesquot; - Journ. Acad. Wash. 5, p. 489, 1915.
Vaughan, T. W. quot;Geological mapping in the western part of the U.S., Centr. America
and the West Indiesquot; - Proc. First Pan Pacific Scientific Conf. Honolulu 3, pp. 695—705,
1921.nbsp;^^

Vaughan, T. W. quot;Correlation of the Tertiary formations of Central America and the
West Indiesquot; - Proc. First Pan Pac. Sc. Conf. Honolulu, 3, pp. 819—845 1921.
Vermunt, L. W. J. and Rutten, M. G. quot;Geol. of Central-Cura9aoquot; and quot;Geology
of the Surroundings of quot;St. Marthaquot; and quot;St. Kruisquot; (Curasao)quot;, Proc. Kon. Ac.
V. Wetensch. te Amsterdam, 34, 1931, resp. no. 2, pp. 271-276 and no. 4, pp. 55 8-563.

52.nbsp;Westermann, J. H. quot;Over de Geologie van Arubaquot; - Handelingen 23 Nederl. Nat.
Geneesk. Congres, 1931.

53.nbsp;Westermann, J. H. quot;Over de Geologie van Arubaquot; - Verslag Geol. sectie Geol.
Mijnb. Gen., Geologie en Mijnbouw no. 14, jrg. 10, 16 Oct. 1931.

54.nbsp;Westermann, J. H. quot;Arubaquot; - Leidsche Geol. Mededeelingen deel 5, Nov. 1931 pp
709—714 (Feestbundel Prof. Martin)

8
11
11
11
13
16
16

18
20
20
20
25

33
33
35

OCCURRENCE, DISTRIBUTION, GEOLOGY AND GENESIS OF THE BRECCIAS 36
OCCURRENCE, DISTRIBUTION, GEOLOGY AND GENESIS OF THE DIABASE-

CONGLOMERATES .......................................36

SHORT OUTLINE OF THE GEOLOGY AND THE GEOMORPHOLOGY
OF ARUBA ........................

Uralite-diabases and Contactmetamorphic Uralite-diabases
Distribution of the Contactmetamorphic Uralite-diabases
Aberrant, Microporphyritic Diabases

occurrence, distribution and geology of the diabasic rocks .
schistose and tuffojd rocks

More or less metamorphic (hornblendized) Diabase-tuffs . .
Non-hornblendized Tuffoid Rocks, little or hardly altered . .
Schisty, Porphyritic Rocks ...............

relation between the not and little hornblendized tuffoid
rocks and the strongly metamorphic tuffs (hornblende

OCCURRENCE, DISTRIBUTION AND GEOLOGY OF THE QUARTZDIORITESnbsp;44
DIORITIC ROCKS CONSOLIDATED BEFORE THE MAIN PART OF THE DIORITES

geology of the contactzones with amphibolitic rocks ....nbsp;108
genesis of the contactrocks, especially of the amphibolitic

Plate I. — Fig. 1. View from the slope of the Hooiberg towards the NE (Diorite
plain, and the hills of the Older formation and of the gabbro massive in the
background), — photo P. Wagenaar Hummelinck. — Fig. 2. Diorite detritus,
diorite monoliths and the cony Hooiberg. — photo L. W. J. Vermunt. — Fig. 3*.
Cove in a diorite monolith, NE of the Hooiberg. — photo M. G. Rutten.

• ■ gt; ■ ' )

1'Î

p, , ,TT _ i^ig 1 Pyroxene-hooibergite (10 x, //nic.). — Fig. 2. Pyroxene-hooibergite, rich in pyroxene and poor in plagioclase-quartz

nq V //nic^ „'pig. 3. Hornblende-vintlite (30 X, //nic.). — Fig. 4. Quartz-hornblende-vintlite; resorbed quartz phenocrysts with
1nbsp;rpnctionrims (30 X, //nic.). — Fig. 5. Porphyritic malchite in contact with quartz-hornblende-biotite-diorite; malchite

inn'^wpr^r. the diorite, and diorite plagioclases partly resorbed (25 X, //nic.). — Fig. 6. Gabbro-aplite (27 x, //nic.). — Fig. 7. Hooibergite
apophyses m tne anbsp;^^ ^nbsp;X, macr.). — Fig. 8. Pyroxene-hooibergite (y, x, macr.).

'Â

' .1

GEOLOGICAL MAP
OF ARUBA

Neth. West-Indies
1 :50.000

• lt;/( A^aorc/

a Chi At ^oe

Het Heraklea kolenbekken (Noord Klein-Azië) en het Donetz kolenbekken
(Rusland) vertoonen zeer groote verwantschap, en vormden resp. de Z. en N.
randslenk van het Boven-Carbonische „Pontische schiereilandquot; (J. L. Wilser —
Geol. Rundsch. 18—1927).

A. Born heeft voor het Rijnsche Leisteengebergte waarschijnlijk kunnen
maken, dat de metamorphose, behalve door plooiingsdruk, voor een zeer belangrijk
deel veroorzaakt is door belastingsdruk (Senckenbergiana 9 —5, 1927).

Thüringer Woud), waarlangs von Seidlitz tertiaire of post-tertiaire blad ver-
schuiving in de Thüringer Horst aanneemt, reeds prae-varistisch is aangelegd
(Centralbl. f. Min. etc. B., 7 — 1928).

Een oude kristallijne kern is op Aruba niet gevonden. De opvattingen
over het bestaan ervan zijn onjuist en berusten op een foutieve interpretatie
van de contactmetamorfe diabaastuffen.

De theorie van R. T. Chamberlin en T. A. Link betreffende de quot;laterally
spreading batholithsquot; en de laccolieth-achtige vorm van de bathohethen is aan-
nemelijk (Joum. of Geol. 35 — 1927).

De groepeering van strand-rolsteenen langs de Westkust van Lake Michigan
(Wisconsin, Illinois) naar grootte en vorm, als beschreven door R. E. Landon
(Journ. of Geol. 38 — 1930), is het gevolg van de afslijting en van het selectief
transport, in ouderlingen samenhang.

Het bestaan van fraaie ,,Karrenfelderquot; in de kalken van de Benedenwindsche
eilanden geeft steun aan de gewijzigde opvatting van W. Salomon betreffende
het voorkomen van ,,Karrenfelderquot; in landen met warm klimaat (Centralbl. f.
Min. etc. B., 15 — 1926).

De opvattingen van O. Jaekel over de morphologische beoordeeling van
de eerste halswervels, steunende op palaeontologische gronden, zijn van waarde
(Anat. Anz. 40 — 1912).

Het probleem van beplanting van buitenwegen in Nederland met boomrijen
verdient nadere bestudeering in verband met natuurbescherming, verkeer en
techniek.

r, '1

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