The north of Blue-Mud Bay has furnished also specimens of ancient sandstone; with columnar rocks, probably of clink-stone. Round Hill, near Point Grindall, a promontory on the north of Morgan's Island, is composed, at the base, of granite; and Mount Caledon, on the west side of Caledon Bay, seems likewise to consist of that rock, as does also Melville Island. This part of the coast has afforded the ferruginous oxide of manganese: and brown hematite is found hereabouts in considerable quantity, on the shore at the base of the cliffs; forming the cement of a breccia, which contains fragments of sandstone, and in which the ferruginous matter appears to be of very recent production; resembling, perhaps, the hematite observed at Edinburgh by Professor Jameson, around cast-iron pipes which had lain for some time in sand.*
(*Footnote. Edinburgh Philosophical Journal, July 1825 page 193.)
The general range of the coast, it will be observed, from Limmen's Bight to Cape Arnhem, is from south-west to north-east; and three conspicuous ranges of islands on the north-western entrance of the Gulf of Carpentaria, the appearance of which is so remarkable as to have attracted the attention of Captain Flinders,* have the same general direction: a fact which is probably not unconnected with the general structure of the country. The prevailing rock in all these islands appears to be sandstone.
(Flinders Volume 2 page 158. See hereafter.)
The line of the main coast from Point Dale to the bottom of Castlereagh Bay, where Captain King's survey was resumed, has also a direction from south-west to north-east, parallel to that of the ranges of islands just mentioned. The low land near the north coast in Castlereagh Bay, and from thence to Goulburn Islands, is intersected by one of the few rivers yet discovered in this part of Australia, a tortuous and shallow stream, named Liverpool River, which has been traced inland to about forty miles from the coast, through a country not more than three feet in general elevation above high-water mark; the banks being low and muddy, and thickly wooded: And this description is applicable also to the Alligator Rivers on the south-east of Van Diemen's Gulf, and to the surrounding country. The outline of the Wellington Hills, however, on the mainland between the Liverpool and Alligator Rivers, is jagged and irregular; this range being thus remarkably contrasted with the flat summits which appear to be very numerous on the north-western coast.
The specimens from Goulburn Islands consist of reddish sandstone, not to be distinguished from that which occurs beneath the coal formation in England. On the west of these islands the coast is more broken, and the outline is irregular: but the elevation is inconsiderable; the general height in Cobourg Peninsula not being above one hundred and fifty feet above the sea, and that of the hills not more than from three to four hundred feet.
On this part of the coast, several hills are remarkable for the flatness of their tops; and the general outline of many of the islands, as seen on the horizon, is very striking and peculiar. Thus Mount Bedwell and Mount Roe, on the south of Cobourg Peninsula; Luxmoore Head, at the west end of Melville Island; the Barthelemy Hills, south of Cape Ford; Mount Goodwin, south of Port Keats; Mount Cockburn, and several of the hills adjacent to Cambridge Gulf, the names given to which during the progress of the survey sufficiently indicate their form, as House-roofed, Bastion, Flat-top, and Square-top Hills; Mount Casuarina, about forty miles north-west of Cambridge Gulf; a hill near Cape Voltaire; Steep-Head, Port Warrender; and several of the islands off that port, York Sound, and Prince Regent's River; Cape Cuvier, about latitude 24 degrees; and, still further south, the whole of Moresby's flat-topped Range, are all distinguished by their linear and nearly horizontal outlines: and except in a few instances, as Mount Cockburn, Steep-Head, Mounts Trafalgar and Waterloo (which look more like hills of floetz-trap) they have very much the aspect of the summits in the coal formation.*
(*Footnote. Captain King, however, has informed me, that in some of these cases, the shape of the hill is really that of a roof, or hayrick; the transverse section being angular, and the horizontal top an edge.)
Sketch 1 of some of the islands off Admiralty Gulf (looking southward from the north-east end of Cassini Island, about latitude 13 degrees 50 minutes, East longitude 125 degrees 50 minutes) has some resemblance to one of the views in Peron's Atlas (plate 6 figure 7): and the outline of the Iles Forbin (plate 8 figure 5, of the same series) also exhibits remarkably the peculiar form represented in several of Captain King's drawings (Sketch 2).