PRESIDENT’S ADDRESS. 730 
An alternative line of migration would be by way of Torres 
Straits. 
The position of the Great Barrier Reef as to North-eastern 
Australia strongly suggests a submerged shore Jine of the conti- 
nent ; 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. 
Mr. Robert L. 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 100 feet below the present sea level, and 
no river could possibly have excavated a channel to this depth 
while the land stcod at its present level. This submergence, in 
all probability, took place after the period to which the extinct 
mammalia belonged.* 
Mr. Jack has also pointed: out to me orally that bays and 
estuaries into which rivers flow on the east coast indicate sub- 
merged valleys, and he has suggested that this comparatively 
recent submergence of the eastern part of Australia gave rise to 
Sydney Harbour on the one hand and Torres Straits on the other. + 
An inspection of the Admiralty chart of Torres Straits between 
Cape York and the nearest part of New Guinea shows, not only 
a number of islands of some size, but innumerable islets and 
reefs studding a sea so shallow that it is only exceptionally that 
in the channels there isa depth of 10 fathoms. Therefore a move- 
ment of elevation of 60 feet would connect Australia and New 
Guinea by land. The 80 to 100 feet of subsidence which Mr. 
Jack assigns to the north-east coast in comparatively recent times 
would do more than merely connect the two lands. 
So far as is yet known, the extinct mammalia to which Myr. 
Jack refers did not extend into New Guinea, and the absence of 
the platypus and the feeble development of the polyprotodont 
fauna in north-eastern Australia is considered by Professor 
Spencer to indicate that they spread northwards rather than 
southwards, { thus negativing the existence of an upraised Torres 
Strait at that time. 
This suggests that, although there had been a land communica~- 
tion which admitted of a certain migration of Australian forms, it 
had ceased before the giant extinct marsupials spread into the 
extreme of Northern Queensland, and according to Mr. Jack that 
would probably have been in Post-Tertiary times.§ It seems 
therefore evident that there was a land communication between 
New Guinea and Australia at a comparatively recent period by 
which the Tasmanians, and subsequently the Australians, might 
* xxxI, vol. 1, pp. 618, 614. fT XXXI. } LII, p. 180. § XXXI, 
