What lapse of time is represented during this period of erosion is a matter of speculation, but it seems certain that the mollusca of the present creeks were also the inhabitants of the waters during the whole period of denudation since the last volcanic eruption.
From the Gulf of Carpentaria in the north, to Darling Downs in the south, however, the fossil remains of extinct mammalia have been found in breccias and indurated muds, which are the representatives of the beds of old watercourses through which the present creeks cut their channels. At Maryvale Creek, in latitude 19 deg. 30 sec. S., good sections of these old brecciated alluvia occur. The fossils from this section, as determined by Professor Owen, are “Diprotodon Australis, Macropus titan, Thylacoles, Phascolomys, Nototherium,” crocodile teeth, etc.
Imbedded in the same matrix occur several genera of mollusca undistinguishable from those inhabiting Maryvale Creek.
The fact of these older alluvia forming both the bed and the banks of the present watercourse, goes to prove that Diprotodon and its allies inhabited the Queensland valleys when they presented little difference in physical aspect or elevation from that of the present time. The crocodile (Crocodilus Australis), however, had then a greater range inland than it has now. A study of these Diprotodon breccias leads to the conclusion that the remains are chiefly entombed in what were the most permanent waterholes in seasons of excessive drought, and that the animals came there in a weak and exhausted state to drink and die, just as bullocks do under similar conditions at the present time.
No human bones, flint flakes, or any kind of native weapons have yet been discovered with the extinct mammalia of Queensland.
CAINOZOIC.
Desert Sandstone.—On the eastern branches of the Upper Flinders and elsewhere, fine sections are exposed of lava resting on horizontal beds of coarse grit and conglomerate, which lie in turn unconformably on olive-coloured and gray shales with interstratified bands and nodules of argillaceous limestone containing fossils of cretaceous affinities. I have called this upper conglomerate series “Desert Sandstone,” from the sandy barren character of its disintegrated soil, which makes the term particularly applicable.
Without doubt, it is the most recent widely-spread stratified deposit developed in Queensland. The denudation of the “Desert Sandstone” since it became dry land has been excessive, but there still remains a large tract “in situ,” and all the available evidence tends to show that this “Desert Sandstone” did at one time cover nearly, if not quite, the whole of Australia. The journals of the two Gregory’s description of the new settlement of Port Darwin, all bear evidence to the continuity of this so-called “Desert Sandstone” over all the extended areas investigated by them.
Augustus Gregory’s description of the sandstones of the Victoria River agrees with those of the “Desert Sandstone” of Queensland, the specimens from either locality being undistinguishable the one from the other, while the same barren soil, the same hostile spinifex, the same fatal poison plant, mark its presence from Perth to Cape York.
In Queensland, the upper beds are ferruginous, white and mottled sandy clays, the lower being coarse alternating grits and conglomerates; the extreme observed thickness has not exceeded 400 feet. A characteristic view of the upper “Desert Sandstone” beds is shown in Betts’ Creek, on the Upper Flinders. Whether these are marine, lacustrine, or estuarine deposits, there is hardly sufficient evidence to show.