But, for this to have been the case, the physical conditions must have been very different from what they are now.

Nearly three hundred miles of open sea now separate Australia from Timor, which island is connected with Java by a chain of broken land divided by straits which are nowhere more than about twenty miles wide.

Evidently there are now great facilities for the natural productions of Java to spread over and occupy the whole of these islands, while those of Australia would find very great difficulty in getting across.

To account for the present state of things, we should naturally suppose that Australia was once much more closely connected with Timor than it is at present; and that this was the case is rendered highly probable by the fact of a submarine bank extending along all the north and west coast of Australia, and at one place approaching within twenty miles of the coast of Timor.

This indicates a recent subsidence of North Australia, which probably once extended as far as the edge of this bank, between which and Timor there is an unfathomed depth of ocean.
I do not think that Timor was ever actually connected with Australia, because such a large number of very abundant and characteristic groups of Australian birds are quite absent, and not a single Australian mammal has entered Timor--which would certainly not have been the case had the lands been actually united.