Narrative of a Survey of the Intertropical and Western Coasts of Australia Volume II Part 59

GROOTE EYLANDT is composed of sandstone, of which two different varieties occur among the specimens. A quartzose reddish sandstone, of moderately fine grain; and a coa.r.s.e reddish compound, consisting almost exclusively of worn pebbles of quartz, some of which are more than half an inch in diameter, with a few rounded pebbles of chalcedony. The latter rock is nearly identical with that of Simms' Island, near Goulburn's Island on the north coast.

CHASM ISLAND, WINCHELSEA ISLAND, and BURNEY'S ISLAND, are of the same materials as Groote Eylandt: and sandstone was found also on the western sh.o.r.e of BLUE-MUD BAY.

On the sh.o.r.e of the mainland, opposite to Groote Eylandt, a little north of lat.i.tude 14 degrees, Mr. Brown observed the common sandy calcareous stone, projecting here and there in ragged fragments.

MORGAN'S ISLAND, in Blue-Mud Bay, north-west of Groote Eylandt, is composed princ.i.p.ally of clink-stone, sometimes indistinctly columnar. But among the specimens are also a coa.r.s.e conglomerate of a dull purplish colour, including pebbles of granular quartz and a fragment of a slaty rock like potstone: the hue and aspect of the compound being precisely those of the oldest sandstones. Reddish quartzose sandstone, of uniform and fine grain. A concretion of rounded quartz pebbles, cemented by ferruginous matter, apparently of recent formation.

ROUND HILL, near Cape Grindall, a prominence east of north from Blue-Mud Bay, was found by Captain Flinders to consist, at the upper part, of sandstone. The specimens of the rocks in its vicinity are, dark grey granite, somewhat approaching to gneiss, with a few specks of garnet; and a calcareous, probably concretional stone, enclosing the remains of sh.e.l.ls, with cavities lined with crystals of calcareous spar.

MOUNT CALEDON, on the mainland, west of Caledon Bay, consists of grey granite, with dark brown mica in small quant.i.ty; and on the sides and top of the hill large loose blocks of that rock were observed, resting upon other blocks.

A small island, near Cape Arnhem, is also composed of granite, in which the felspar has a bluish hue.

Smaller of the MELVILLE ISLANDS, north-east of Melville Bay.* A botryoidal ma.s.s of ferruginous oxide of manganese, approaching to hemat.i.te; the fissures in some places occupied by carbonate of lime.

(*Footnote. The relative position of the islands and bays on this part of the coast is represented in the enlarged Map.)

MELVILLE BAY. Granite, composed of grey and somewhat bluish felspar, dark brown mica, and a little quartz; containing minute disseminated specks of molybdena, and indistinct crystals of pale red garnet.

RED CLIFFS, south-west of Arnhem Bay; on the line of the first chain of islands mentioned by Captain Flinders. (See the Map, figure 3.) Friable conglomerate, of a full brick-red colour, consisting of minute grains of quartz, with a large proportion of ochreous matter.

MALLISON'S ISLAND. (Map, figure 4.) The cliffs of this island are composed of a fissile primitive rock, on which sandstone reposes in regular beds. The specimen of the former resembles gneiss, or mica slate, near the contact with granite: the sandstone is thick-slaty, quartzose, of a reddish hue, with mica disseminated on the surfaces of the joints; and one face of the specimen is incrusted with quartz crystals, thinly coated with botryoidal hemat.i.te. Light grey quartzose sandstone of a fine grain, with a thin coating of brown hemat.i.te, was also found in this island: And a breccia, consisting of angular fragments of sandstone, cemented by thin, vein-like, coatings of dark brown hemat.i.te, was found there, in loose blocks at the bottom of perpendicular cliffs. The specimen of this breccia is attached to a plate of granular quartz, and may possibly have been part of a vein.

The sh.o.r.e of INGLIS' ISLAND, the largest of the ENGLISH COMPANY'S RANGE (2. 2. 2. in the Map) is formed of flat beds, of a slaty argillaceous rock, which breaks into rhomboidal fragments; but the specimen is indistinct. Ferruginous ma.s.ses, probably consisting of brown hemat.i.te, come also from this island.

ASTELL'S ISLAND, north-east of Inglis' Isle. Very fine-grained greyish-white quartzose sandstone; identical with that of Mallison's Island, and very closely resembling some of the specimens from Prince Regent's and Hunter's Rivers.

Among the remaining islands of this range, BOSANQUET'S, COTTON'S, and POBa.s.sOO's Isles, were found by Mr. Brown to consist, in a great measure, of sandstone, of the same character with the specimens above-mentioned.

POBa.s.sOO'S ISLAND, a small islet south-east of Astell's Isle.

Fine-grained, somewhat reddish, sandstone. Another specimen of sandstone is friable, of a light flesh-red colour, and apparently composed of the debris of granite. A crystalline rock, consisting of greenish-grey hornblende, with a very small proportion of felspar (Hornblende rock ?).

Fragment, apparently from a columnar ma.s.s, of a stone intermediate between clink-stone and compact felspar.

Such of the English Company's Islands as were examined by Captain Flinders, are stated by him to consist, in the upper part, of a grit, or sandstone, of a close texture; the lower part being argillaceous, and stratified, and separating into pieces of a reddish colour, resembling flat tiles. The strata-dip to the west, at an angle of about 15 degrees.

South-west bay of GOULBURN'S SOUTH ISLAND, two hundred and fifty miles west of the Gulf of Carpentaria (Narrative 1). Coa.r.s.e-grained reddish quartzose conglomerate and sandstone; resembling the older sandstones of England and Wales, and especially the mill-stone grit beneath the coal formation. Fine greyish-white pipe-clay; of which about thirty feet in thickness were visible, apparently above the sandstone last mentioned.

Coa.r.s.e-grained, ferruginous sandstone, containing fragments of quartz, from above the pipe-clay. The appearance of the cliff from which these specimens were taken, is represented in the view of the bay on the south of Goulburn Island (volume 1); and a distant head in the view consists of the same materials.

SIMMS ISLAND, on the west of Goulburn's south Island (Narrative 1) is composed of a reddish conglomerate, nearly identical with some of the specimens above-mentioned.

The western side of LETHBRIDGE BAY, on the north of MELVILLE ISLAND, consists of a range of cliffs like those at Goulburn's Island; the upper part being red, the lower white and composed of pipe-clay. The western extremity of BATHURST ISLAND, between CAPE HELVETIUS and CAPE FOURCROY, is also formed of cliffs of a very dark red colour.

LACROSSE ISLAND, at the mouth of CAMBRIDGE GULF, about one hundred miles from Port Keats. Reddish, very quartzose sandstone; from a stratum which dips to the south-east, at an angle of about ten or fifteen degrees.

Micaceous and argillaceous fissile sandstone, of purplish and greenish hues, in patches, or occasionally intermixed; precisely resembling the rock of Brecon, in South Wales, and, generally, the old red sandstone of the vicinity of Bristol and the confines of England and Wales.

Fine-grained thin-slaty sandstone, resembling certain beds of the coal formation, or of the millstone grit, is found in large ma.s.ses, under an argillaceous cliff, on the north side of Lacrosse Island.

The specimens from the interior of Cambridge Gulf are from ADOLPHUS ISLAND, and consist of reddish and grey sandstone, more or less decomposed.

VANSITTART BAY, about one hundred and forty miles north-west of Cambridge Gulf. Reddish quartzose sandstone, or quartz-rock. Indistinct specimens of greenstone, with adhering quartz; apparently a primitive rock.

PORT WARRENDER, at the bottom of Admiralty Gulf, about forty miles south-west of Vansittart Bay (Narrative volume 1). Epidote and quartz, in small crystals confusedly interlaced; apparently from veins, or nests, but unaccompanied by any portion of the adjacent rock. The structure in one of these specimens approaches to the amygdaloidal. A compact greenish stone, with disseminated crystalline spots of epidote, and of quartz, and apparently consisting of an intimate mixture of those minerals, is also among the specimens from Port Warrender.

All these specimens are from detached water-worn ma.s.ses at the foot of Crystal Head, on the south-west of the port. The summit of the head is flat and tabular, and the rocks in the vicinity are described by Captain King as consisting of siliceous sandstone. Chalcedony, apparently from amygdaloid of the trap formation, was also found at Port Warrender.

The epidote of this place is in general of a pale-greenish colour, but is mixed with, and sometimes appears to pa.s.s into, spots of a rich purplish-brown. The specimens resemble generally the epidote of Dauphiny and Siberia; but Mr. Levy, who has been so good as to examine them, informs me that the crystals exhibit some modifications not described either by Hauy, or by Mr. Haidinger in his paper on this mineral, and which are probably peculiar to this locality.

WATER ISLAND, on the west side of CAPE VOLTAIRE, at the south-west entrance of Port Warrender, is described (volume 1) as consisting of quartzose sandstone; as is also KATER ISLAND, in Montagu Sound. And the same rock appears to occur throughout the islands on this part of the coast. (Narrative 1.)

MONTAGU SOUND, about five-and-twenty miles south-west of ADMIRALTY GULF (Narrative 1). Greyish granular quartz; like that of the Lickey Hill, in Worcestershire. Fine-grained quartzose sandstone, of a purplish hue, resembling a rock on the banks of the Severn, near Bridgenorth. Grey and reddish sandstone; apparently composed of the debris of granite, and very nearly resembling that of Simms Island above-mentioned.

HUNTER'S RIVER, falling into YORK SOUND, on the north-east side. Somewhat coa.r.s.e reddish-white sandstone; like that of the coal formation, and some varieties of millstone grit. Fine-grained, reddish-grey quartzose sandstone, having the appearance of stratification, and resembling the rocks of Cambridge Gulf.

ROE'S RIVER, at the eastern termination of York Sound (Narrative 1) runs between precipitous banks of sandstone, in nearly horizontal strata, which rise to the height of three hundred feet.

CAREENING BAY, between York Sound and Prince Regent's River (Narrative volume 1. See the plate volume 1). Crystalline epidote, and whitish quartz, apparently from a vein. Purplish-brown epidote, with small nests or concretions of green epidote and quartz; forming a sort of amygdaloid.

Conglomerate, containing angular fragments of yellowish-grey quartz-rock, in a base of compact epidote. A nearly uniform greenish compound of epidote intimately mixed with quartz, also occurs at this place. Flat lamellar chalcedony. Very fine-grained reddish-grey quartzose sandstone, with traces of a slaty structure, resembling that of York Sound, and Cambridge Gulf, was found in the north-east end of this bay; and fine-grained greenstone, on the summit of the adjacent hills.

Several of these specimens are almost identical with those of Port Warrender; from which place Careening Bay is distant about sixty miles.

BAT ISLAND (Narrative volume 1) western entrance of Careening Bay. Quartz from thin veins, with particles of an adhering rock, probably chlorite-slate. Quartz, containing disseminated hemat.i.tic iron-ore and copper pyrites. Quartz crystals, with chalcedony, from nodules in amygdaloid. Quartz with specular iron ore. Greenstone, with chalcedony and copper pyrites. A decomposed stone, probably consisting of wacke. The specimens of trap-rocks from this place are from a cavern.

GREVILLE ISLAND, near the entrance of Prince Regent's River. Reddish, coa.r.s.ely granular, siliceous sandstone; in horizontal strata, intersected by veins of crystallized quartz.*

(*Footnote. Narrative volume 2.)

HALF-WAY BAY, within Prince Regent's River on the west of the entrance, near Greville Island. Hornblende rock ? nearly agreeing with that of Poba.s.soo's Island, on the north-west of the Gulf of Carpentaria (see above). Calcedony, apparently from nodules in amygdaloid. Greenish quartz, approaching to heliotrope. Red, somewhat slaty jasper, mixed with quartz and chalcedony, and containing specular iron ore.

The specimens from this place much resemble some of those from Sotto i Sa.s.si, in the Val di Fa.s.sa in the Tyrol, which I have seen in the collection of Mr. Herschel; and which consist of reddish jasper with chalcedony, and a greenish flinty stone, like heliotrope, the whole belonging to the trap-formation.

POINT CUNNINGHAM, east of south from Cape Leveque, and about one hundred and fifty miles south-west of Prince Regent's River. Very compact and fine-grained reddish granular quartz, with a glistening l.u.s.tre, and flat conchoidal fracture. This stone, though so compact in the recent fracture, has distinct traces of stratification on the decomposed surface, which is of a dull reddish hue. Bright red ferruginous granular quartz (Eisen-kiesel ?) with a glistening l.u.s.tre, and a somewhat porous texture. A specimen of the soil of the hills at Cygnet Bay, consists of very fine reddish-yellow quartzose sand. A large rounded pebble, consisting of ferruginous granular quartz, of a dark purplish-brown colour, and considerable density, was found here; near a fireplace of the natives, by whom it is used for making their hatchets; with a fragment of a calcareous incrustation, like that of the west coast hereafter mentioned.

The next specimens in Captain King's collection--a s.p.a.ce of more than three hundred miles on this coast not having been examined by him--are from MALUS ISLAND, in Dampier's Archipelago (see Narrative volume 1) they consist of fine-grained greenstone, and what appears to be a basaltic rock, of amygdaloidal structure.

DIRK HARTOG'S ISLAND, west of Shark's Bay. A compound of rather fine-grained translucent quartzose sand, cemented by carbonate of lime, of various shades of reddish and yellowish grey. This stone has in some places the structure of a breccia; the angles of the imbedded fragments, which are from half an inch to two inches in diameter, being very distinct--but in other parts, the fracture exhibits the appearance of roundish nodules, composed of concentric sh.e.l.ls--or bags as it were, of calcareous matter, which vary in colour, and are filled with a mixture of the same substance and quartzose sand: and the s.p.a.ces between these nodules are likewise occupied by a similar compound.*

(*Footnote. The following description given by the French naturalists of the rocks at Bernier's Islands, was probably taken from a large suite of specimens; and M. Peron states (1 page 204) that it is strictly applicable to all the adjacent parts of the continent, and of the islands that were examined by the French voyagers:

Le sable du rivage (de l'ile Bernier) est quartzeux, mele d'une grande proportion de debris calcaires fortement attenues. La substance de l'ile meme se compose, dans ses couches inferieures, d'un gres calcaire coquillier, tantot blanchatre, tantot rougeatre, depose par couches horizontales, dont l'epaisseur varie de 2 a 8 decimetres (7 a 11 pouces) et qui toutes etant tres uniformes dans leur prolongement, pourroient offrir a la maconnerie des pierres de construction naturellement taillees.

Les coquilles incrustees dans ces ma.s.sifs des roches sont presque toutes univalves; elles apartiennent plus particulierement au genre Natice de M.

de Lamarck, et ont les plus grands rapports avec l'espece de Natice qui se trouve vivante au pied de ces rochers. Elles sont sans doute petrifiees depuis bien des siecles, car, outre qu'il est tres difficile de les retirer intactes du milieu de ces gres, tant leur adhesion avec eux est intime, on les observe encore a plus de 50 metres (150 pieds) au dessus du niveau actuel de la mer.

Quelque regularite que ces bancs puissent affecter dans leur disposition generale, ils ne sont cependant pas tous h.o.m.ogenes dans leur substance; il est sur-tout une variete de ces roches plus remarquable par sa structure. Ce sont des galets calcaires, agreges dans une terre sablonneuse ocracee, qui leur est tellement adherente, qu'on ne sauroit detruire cette espece de gangue sans les briser eux memes. Tous ces galets affectent la forme globlueuse, et se composent d'un grand nombre de zones concentriques, qui se developpent autour d'un noyau central d'un gres scintillant et brunatre. Ces diverses couches ont a peine quelques millimitres d'epaisseur, et affectent des nuances agreables, qui varient depuis le rouge-fonce jusqu'au jaune-clair. La disposition generale de cette breche lui donne donc quelques rapports grossiers avec le granit globuleux de l'ile de Corse; et, par ses couches rubanees, concentriques, elle a quelque chose de l'aspect des Agathes-Onyx...Les bancs de gres divers dont je viens de parler, const.i.tuent, a bien dire, la ma.s.se entiere du pays qui nous occupe, etc. (Volume 1 page 110. See also Freycinet page 187.)

The cementing limestone in the rock of this island, is very like some of the more compact portions of the stone of Guadaloupe, which contains the human skeletons, the hardness and fracture being nearly the same in both.

The chief difference of these rocks seems to arise from the nature of the cemented substances; which, in the Guadaloupe stone, being themselves calcareous, are incorporated, or melted as it were, into the cement, by insensible gradation;* while the quartzose sand, in that of Dirk Hartog's Island, is strongly contrasted with the calcareous matter that surrounds it.** But, wherever the imbedded fragments in the latter consist of limestone, their union with the cement is complete.

(*Footnote. See Mr. Koenig's Paper. Philosophical Transactions volume 104 1814 page 107 etc.)