In all probability, Australia was severed into two or more great continental islands lying to the east and west of a large Mediterranean sea. In this latter, and in the ocean waters beyond the islands, were laid down marine beds. Those of the Mediterranean sea, widely developed in Queensland, Northern Territory, and South Australia, and to a smaller extent in New South Wales and Western Australia, supply vast quantities of artesian water. In early Tertiary time the whole continent was subjected to a tilting movement, rising on the north and subsiding on the south. The former portion became dry land, but the sea transgressed extensively over Tasmania, Victoria, South Australia, and Western Australia, and laid down thick beds of limestone.
Climatic conditions appear to have been quite mild.
Extensive volcanic eruptions occurred along the borders of the old cretaceous sea. In later Tertiary time came the gradual uplift, expelling the sea from the continental surface, and causing the formation of extensive plateau surfaces. Volcanic action on a large scale was widespread, and, in Western Victoria and South-eastern South Australia, continued to a very recent date. That the climate of Australia was much moister during this period than it is at the present day is shown by evidences of former great extension of lake basins now dry or much shrunken, and by the remains of gigantic extinct animals, including crocodiles and turtles, in the now desert areas of Central Australia. A third great glacial epoch occurred during late Tertiary time.