Volume II Part 59 (1/2)

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.