between Timor and Australia, twenty miles in width.[1] The former, which is only fifteen miles wide, has sufficed to stop the advance of the larger mammals from the Asiatic to the Austral region, and the latter strait has similarly prevented the Australian mammals from entering Timor.
If this was the line of migration of the early Tasmanians and Australians, we should have to assume either that they were able to cross the deep sea straits on rafts or in bark canoes, or that these sea straits were at such a comparatively recent geological time much narrower than the soundings suggest.
An alternative line of migration would be by way of Torres Strait.
The position of the Great Barrier Reef as to north-eastern Australia strongly suggests a submerged shore line of the continent; and if so, the numerous islands, islets, and reefs between Cape York Peninsula and New Guinea also suggest the former existence of a land connection now broken by subsidence.
Dr. Jack points out that from Cape Palmerston to the Herbert River the coast is fringed by a strip of alluvial flat, composed of alternating beds of clay, sand, and gravel, the latter probably belonging to river beds. The old land surface, as proved by boring, is from 80 to l00 feet below the present sea-level, and no river could possibly have excavated a channel to this depth while the land stood at its present level. This submergence, in all probability, took place after the period to which the extinct mammalia belonged.[2]
Dr. Jack has also pointed out to me orally, that bays and estuaries into which rivers flow on the east coast indicate submerged valleys, and suggested that this comparatively recent submergence of the eastern part of Australia gave rise to Sydney Harbour on the one hand and Torres Strait on the other.
An inspection of the Admiralty Chart of Torres Strait
