Page:A sketch of the physical structure of Australia.djvu/103

91 events have ever since remained above the level of the sea. During some tertiary period, however, it is clear that it was again partially submerged, that a sea of no great depth extended over by far the greater portion of Australia, in which sea was deposited the beds of limestone and ferruginous sandstone, and the loose and incoherent sands that form the great plains of which we know so large and I believe so much larger a part of the country is composed. During this tertiary period we should have one long island, or chain of islands, running along what is now the great eastern chain of Australia; a similar island, or islands, but of much less extent, formed of the chain of South Australia, with many smaller groups between the two in what is now Australia Felix. These latter were probably added to at this period by a number of volcanic cones, that probably arose above the level of the sea from the volcanic foci that certainly found vent in its bed. There would probably be another group of islands formed of the high lands of Western Australia, and again another running probably east and west where we now have high land on the north-west coast, and in the interior, south of Port Essington. After this partial submergence of the country, it has again been elevated above the sea, and left in its present condition. This geological history would account for the present physical features of the country, and likewise for the specific differences which may be