Volume II Part 58 (1/2)
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.