Captain Flinders, in describing the position of the chains of islands on the north-west coast of Carpentaria, Wessel"s, the English Company"s, and Bromby"s Islands, remarks, that he had "frequently observed a great similarity both in the ground plans, and the elevations of hills, and of islands, in the vicinity of each other, but did not recollect another instance of such a likeness in the arrangement of cl.u.s.ters of islands."*
The appearances which called for this observation, from a voyager of so much sagacity and experience in physical geography, must probably have been very remarkable; and, combined with information derivable from the charts, and from the specimens for which we are indebted to Captain King and Mr. Brown, they would seem to point out the arrangement of the strata on the northern coasts of New Holland.
(*Footnote. The following are the proportions a.s.signed by Captain de Freycinet to the princ.i.p.al divisions of the globe. Voyage aux Terres Australes page 107.
COLUMN 1: DIVISION OF THE GLOBE.
COLUMN 2: AREA IN FRENCH LEAGUES SQUARE.
COLUMN 3: PROPORTION.
Asia : 2,200,000 : 17.
America : 2,100,000 : 17.
Africa : 1,560,000 : 12.
Europe : 501,875 : 4.
Australia : 384,375 : 3.
The most remote points from the coast of New South Wales, to which the late expeditions have penetrated (and the interior has never yet been examined in any other quarter) are not above 500 miles, in a direct line from the sea; the average width of the island from east to west being more than 2000 miles, and from north to south more than 1000 miles.)
(*Footnote. Flinders 5 2 page 246; and Charts, Plates 14 and 15. King"s Charts, Plate 4.)
Of the three ranges which attracted Captain Flinders" notice (see the Map) the first on the south-east (3, 4, 5, 6, 7) is that which includes the Red Cliffs, Mallison"s Island, a part of the coast of Arnhem"s Land, from Cape Newbold to Cape Wilberforce, and Bromby"s Isles; and its length, from the mainland (3) on the south-west of Mallison"s Island, to Bromby"s Isles (7) is more than fifty miles, in a direction nearly from south-west to north-east. The English Company"s Islands (2, 2, 2, 2) at a distance of about four miles, are of equal extent; and the general trending of them all, Captain Flinders states (page 233) is nearly North-East by East, parallel with the line of the main coast, and with Bromby"s Islands. Wessel"s Islands (1, 1, 1, 1) the third or most northern chain, at fourteen miles from the second range, stretch out to more than eighty miles from the mainland, likewise in the same direction.
It is also stated by Captain Flinders, that three of the English Company"s Islands which were examined, slope down nearly to the water on their west sides; but on the east, and more especially the south-east, they present steep cliffs; and the same conformation, he adds, seemed to prevail in the other islands.* If this structure occurred only in one or two instances, it might be considered as accidental; but as it obtains in so many cases, and is in harmony with the direction of the ranges, it is not improbably of still more extensive occurrence, and would intimate a general elevation of the strata towards the south-east.
(*Footnote. Flinders Volume 2 page 235.)
Now on examining the general map, it will be seen, that the lines of the coast on the mainland, west of the Gulf of Carpentaria, between Limmen"s Bight and Cape Arnhem--from the bottom of Castlereagh Bay to Point Dale--less distinctly from Point Pearce, lat.i.tude 14 degrees 23 minutes, longitude 129 degrees 18 minutes, to the western extremity of Cobourg Peninsula, and from Point Coulomb, lat.i.tude 17 degrees 20 minutes, longitude 123 degrees 11 minutes, to Cape Londonderry, have nearly the same direction; the first line being about one hundred and eighty geographical miles, the second more than three hundred, and the last more than four hundred miles, in length.* And these lines, though broken by numerous irregularities, especially on the north-west coast, are yet sufficiently distinct to indicate a probable connexion with the geological structure of the country; since the coincidence of similar ranges of coast with the direction of the strata, is a fact of very frequent occurrence in other parts of the globe.** And it is observable that considerable uniformity exists in the specimens, from the different places in this quarter of New Holland which have been hitherto examined; sandstone, like that of the older formations of Europe occurring generally on the north and north-west coasts, and appearing to be extensively diffused on the north-west of the Gulf of Carpentaria, where it reposes upon primitive rocks.***
(*Footnote. It is deserving of notice, that the coast of Timor, the nearest land on the north-west, at the distance of about 300 miles, is also nearly straight, and parallel to the Coast of New Holland in this quarter: part of the mountainous range, of which that island consists, being probably more than 9000 feet high; and its length, from the north-eastern extremity to the South-West of the adjoining island of Rottee, about 300 miles. But, unfortunately for the hypothesis, a chain of islands immediately on the north of Timor, is continued nearly in a right line for more than 1200 miles (from Sermatta Island to the south-eastern extremity of Java) in a direction FROM EAST TO WEST. This chain, however, contains several volcanoes, including those of Sumbawa, the eruption of which, in 1815, was of extraordinary violence. See Royal Inst. Journal volume 1 1816 page 248 etc.
At Lacrosse Island, in the mouth of Cambridge Gulf, on the north-west coast of New Holland, the beds rise to the North-West: their direction consequently is from South-West to North-East; and the rise towards the high land of Timor. The intervening sea is very shallow.)
(**Footnote. A remarkable case of this kind, which has not, I believe, been noticed, occurs in the Mediterranean; and is conspicuous in the new chart of that sea, by Captain W.H. Smyth. The eastern coast of Corsica and Sardinia, for a s.p.a.ce of more than two hundred geographical miles being nearly rectilinear, in a direction from north to south; and, Captain Smyth has informed me, consisting almost entirely of granite, or, at least, of primitive rocks. The coast of Norway affords another instance of the same description; and the details of the ranges in the interior of England furnish several examples of the same kind, on a smaller scale.)
(***Footnote. The coastlines nearly at rightangles to those above-mentioned--from the South-East of the Gulf of Carpentaria to Limmen"s Bight, from Cape Arnhem to Cape Croker, and from Cape Domett to Cape Londonderry--have also a certain degree of linearity; but much less remarkable, than those which run from South-West to North-East.)
The horn-like projection of the land, on the east of the Gulf of Carpentaria, is a very prominent feature in the general map of Australia, and may possibly have some connexion with the structure just pointed out.
The western sh.o.r.e of this horn, from the bottom of the gulf to Endeavour Straits, being very low; while the land on the east coast rises in proceeding towards the south, and after pa.s.sing Cape Weymouth, lat.i.tude 12 degrees 30 minutes, is in general mountainous and abrupt; and Captain King"s specimens from the north-east coast show that granite is found in so many places along this line as to make it probable that primitive rocks may form the general basis of the country in that quarter; since a lofty chain of mountains is continued on the south of Cape Tribulation, not far from the sh.o.r.e, throughout a s.p.a.ce of more than five hundred miles. It would carry this hypothesis too far to infer that these primitive ranges are connected with the mountains on the west of the English settlements near Port Jackson, etc., where Mr. Scott has described the coal-measures as occupying the coast from Port Stevens, about lat.i.tude 33 degrees to Cape Howe, lat.i.tude 37 degrees, and as succeeded, on the eastern ascent of the Blue Mountains, by sandstone, and this again by primitive strata:* But it may be noticed that Wilson"s Promontory, the most southern point of New South Wales, and the princ.i.p.al islands in Ba.s.s Strait, contain granite; and that primitive rocks occur extensively in Van Diemen"s Land.
(*Footnote. Annals of Philosophy June 1824.)
The uniformity of the coastlines is remarkable also in some other quarters of Australia; and their direction, as well as that of the princ.i.p.al openings, has a general tendency to a course from the west of south to the east of north. This, for example, is the general range of the south-east coast, from Cape Howe, about lat.i.tude 37 degrees, to Cape Byron, lat.i.tude 29 degrees, or even to Sandy Cape, lat.i.tude 25 degrees; and of the western coast, from the south of the islands which enclose Shark"s Bay, lat.i.tude 26 degrees, to North-west Cape, about lat.i.tude 22 degrees. From Cape Hamelin, lat.i.tude 34 degrees 12 minutes, to Cape Naturaliste, lat.i.tude 33 degrees 26 minutes, the coast runs nearly on the meridian. The two great fissures of the south coast, Spencer"s, and St.
Vincent"s Gulfs, as well as the great northern chasm of the Gulf of Carpentaria, have a corresponding direction; and Captain Flinders (Chart 4) represents a high ridge of rocky and barren mountains, on the east of Spencer"s Gulf, as continued, nearly from north to south, through a s.p.a.ce of more than one hundred geographical miles, between lat.i.tude 32 degrees 7 minutes and 34 degrees. Mount Brown, one of the summits of this ridge, about lat.i.tude 32 degrees 30 minutes, being visible at the distance of twenty leagues.
The tendency of all this evidence is somewhat in favour of a general parallelism in the range of the strata, and perhaps of the existence of primary ranges of mountains on the east of Australia in general, from the coast about Cape Weymouth* to the sh.o.r.e between Spencer"s Gulf and Cape Howe. But it must not be forgotten, that the distance between these sh.o.r.es is more than a thousand miles in a direct line; about as far as from the west coast of Ireland to the Adriatic, or double the distance between the Baltic and the Mediterranean. If, however, future researches should confirm the indications above mentioned, a new case will be supplied in support of the principle long since advanced by Mr.
Mich.e.l.l,** which appears (whatever theory be formed to explain it) to be established by geological observation in so many other parts of the world, that the outcrop of the inclined beds, throughout the stratified portion of the globe, is everywhere parallel to the longer ridges of mountains, towards which, also, the elevation of the strata is directed.
But in the present state of our information respecting Australia, all such general views are so very little more than mere conjecture, that the desire to furnish ground for new inquiry, is, perhaps, the best excuse that can be offered for having proposed them.
(*Footnote. The possible correspondence of the great Australian Bight, the coast of which in general is of no great elevation, with the deeply-indented Gulf of Carpentaria, tending, as it were, to a division of this great island into two, accords with this hypothesis of mountain ranges: but the distance between these recesses, over the land at the nearest points, is not less than a thousand English miles. The granite, on the south coast, at Investigator"s Islands, and westward, at Middle Island, Cape Le Grand, King George"s Sound, and Cape Naturaliste, is very wide of the line above-mentioned, and nothing is yet known of its relations.)
(**Footnote. On the Cause of Earthquakes. Philosophical Transactions 1760 volume 51 page 566 to 585, 586.)
DETAILED LIST OF SPECIMENS.
The specimens mentioned in the following list have been compared with some of those of England and other countries, princ.i.p.ally in the cabinets of the Geological Society, and of Mr. Greenough; and with a collection from part of the confines of the primitive tracts of England and North Wales, formed by Mr. Arthur Aikin, and now in his own possession. Captain King"s collection has been presented to the Geological Society; and duplicates of Mr. Brown"s specimens are deposited in the British Museum.
RODD"S BAY, on the East Coast, discovered by Captain King, about sixty miles south of Cape Capricorn.* Reddish sandstone, of moderately-fine grain, resembling that which in England occurs in the coal formation, and beneath it (mill-stone grit). A sienitic compound, consisting of a large proportion of reddish felspar, with specks of a green substance, probably mica; resembling a rock from Shap in c.u.mberland.
(*Footnote. In Captain King"s collection are also specimens found on the beach at Port Macquarie, and in the bed of the Hastings River, of common serpentine, and of botryoidal magnesite, from veins in serpentine. The magnesite agrees nearly with that of Baudissero, in Piedmont. (See Cleaveland"s Mineralogy 1st edition page 345.)
CAPE CLINTON, between Rodd"s Bay and the Percy Islands. Porphyritic conglomerate, with a base of decomposed felspar, enclosing grains of quartz and common felspar, and some fragments of what appears to be compact epidote; very nearly resembling specimens from the trap rocks* of the Wrekin and Breeden Hills in Shropshire. Reddish and yellowish sandy clay, coloured by oxide of iron, and used as pigments by the natives.
(*Footnote. By the terms Trap, and Trap-formation, which I am aware are extremely vague, I intend merely to signify a cla.s.s of rocks, including several members, which differ from each other considerably in mineralogical character, but agree in some of their princ.i.p.al geological relations; and the origin of which very numerous phenomena concur in referring to some modification of volcanic agency. The term Greenstone also is of very loose application, and includes rocks that exhibit a wide range of characters; the predominant colour being some shade of green, the structure more or less crystalline, and the chief ingredients supposed to be hornblende and felspar, but the components, if they could be accurately determined, probably more numerous and varied, than systematic lists imply.)
PERCY ISLANDS, about one hundred and forty miles north of Cape Capricorn.
Compact felspar of a flesh-red hue, enclosing a few small crystals of reddish felspar and of quartz. This specimen is marked "general character of the rocks at Percy Island," and very much resembles the compact felspar of the Pentland Hills near Edinburgh, and of Saxony. Coa.r.s.e porphyritic conglomerate, of a reddish hue. Serpentine. A trap-like compound, with somewhat the aspect of serpentine, but yielding with difficulty to the knife. This specimen has, at first sight, the appearance of a conglomerate, made up of portions of different hues, purplish, brown, and green; but the coloured parts are not otherwise distinguishable in the fracture: It very strongly resembles a rock which occurs in the trap-formation, near Lyd-Hole, at Pont-y-Pool, in Shropshire. Slaty clay, with particles of mica, like that which frequently occurs immediately beneath beds of coal.
REPULSE ISLAND, in Repulse Bay, about one hundred and twenty miles north-west of the Percy Islands. Indistinct specimens, apparently consisting of decomposed compact felspar. A compound of quartz, mica, and felspar, having the appearance of re-composed granite.
CAPE CLEVELAND, about one hundred and twenty miles north of Repulse Island. Yellowish-grey granite, with brown mica; "from the summit of the hill." Reddish granite, of very fine grain; with the aspect of sandstone.
Dark grey porphyritic hornstone, approaching to compact felspar, with imbedded crystals of felspar.
CAPE GRAFTON, about one hundred and eighty miles west of north from Cape Cleveland. Close-grained grey and yellowish-grey granite, with brown mica. A reddish granitic stone, composed of quartz, felspar, and tourmaline.
ENDEAVOUR RIVER, about one hundred miles west of north from Cape Grafton.
Grey granite of several varieties; from a peaked hill under Mount Cook and its vicinity. Granular quartz-rock of several varieties: and indistinct specimens of a rock approaching to talc-slate.
LIZARD ISLAND, about fifty miles east of north from Endeavour River. Grey granite, consisting of brown and white mica, quartz, and a large proportion of felspar somewhat decomposed.
CLACK ISLAND, near Cape Flinders, on the north-west of Cape Melville, about ninety miles north-west of Lizard Island. Smoke-grey micaceous slaty-clay, much like certain beds of the old red sandstone, where it graduates into grey wacke. This specimen was taken from a horizontal bed about ten feet in thickness, reposing upon a ma.s.s of pudding-stone, which included large pebbles of quartz and jasper; and above it was a ma.s.s of sandstone, more than sixty feet thick. (Narrative volume 2.)
SUNDAY ISLAND, near Cape Grenville, about one hundred and seventy miles west of north from Cape Melville. Compact felspar, of a flesh-red colour; very nearly resembling that of the Percy Islands, above-mentioned.
GOOD"S ISLAND, one of the Prince of Wales group, about lat.i.tude 10 degrees, thirty-four miles north-west of Cape York. The specimens, in Mr.
Brown"s collection from this place, consist of coa.r.s.e-slaty porphyritic conglomerate, with a base of greenish-grey compact felspar, containing crystals of reddish felspar and quartz. This rock has some resemblance to that of Clack Island above-mentioned.
SWEER"S ISLAND, south of Wellesley"s group, at the bottom of the Gulf of Carpentaria. A stalact.i.tic concretion of quartzose sand, and fine gravel, cemented by reddish carbonate of lime; apparently of the same nature with the stem-like concretions of King George"s Sound: (See hereafter.) In this specimen the tubular cavity of the stalact.i.te is still open.
The sh.o.r.e, in various parts of this island, was found to consist of red ferruginous matter (Bog-iron-ore ?) sometimes unmixed, but not unfrequently mingled with a sandy calcareous stone; and in some places rounded portions of the ferruginous matter were enveloped in a calcareous cement.
BENTINCK ISLAND, near Sweer"s Island. A granular compound, like sandstone recomposed from the debris of granite. Brown hemat.i.te, enclosing quartzose sand.
PISONIA ISLAND, on the east of Mornington"s Island, is composed of calcareous breccia and pudding-stone, which consist of a sandy calcareous cement, including water-worn portions of reddish ferruginous matter, with fragments of sh.e.l.ls.
NORTH ISLAND, one of Sir Edward Pellew"s group. Coa.r.s.e siliceous sand, concreted by ferruginous matter; which, in some places, is in the state of brown hemat.i.te. Calcareous incrustations, including fragments of madrepores, and of sh.e.l.ls, cemented by splintery carbonate of lime.
CAPE-MARIA ISLAND, in Limmen"s Bight, was found by Mr. Brown to be composed princ.i.p.ally of sandstone. The specimens from this place, however, consist of grey splintery hornstone, with traces of a slaty structure; and of yellowish-grey flint, approaching to chalcedony; with a coa.r.s.e variety of cacholong, containing small nests of quartz crystals.