president's address — SECTION D. 117 



Thus, whilst the struthious birds undoubtedly spread south- 

 wards from North-east Australia towards Tasmania, in all 

 probability the polyprotodont marsupials came down from the 

 north-west to the south-west then across to the east, bein^ 

 forced to travel further and further south by the encroaching 

 Cretaceous sea. There was in Cretaceous times little or 

 probably no hindrance to their spreading over the south-east 

 part formed by what is now Victoria and Tasmania, but 

 towards the north-east they could only pass along the com- 

 paratively narrow belt of high land which lay between the 

 inland Cretaceous sea and the open ocean. 



At some period during Tertiary times as indicated by the 

 deposits in South Victoria, in North Tasmania and on the 

 islands of Bass Straits, and comparatively early in this period, 

 Tasmania began to be gradually separated off from the main- 

 land. Previously, however, to this separation the genera and 

 species of existing polyprotodorits had largely been developed. 

 The Dividing Range was possibly higher then than it is now 

 — at all events, we find, in addition to widely-spread forms, a 

 set of species on the south and east not present on the north 

 and west and another on the north and west not present on 

 the south and east. 



When Tasmania became separated off it contained a series 

 of forms identical, so far as genera are concerned, with those 

 of what is now Victoria and in species almost identical with 

 those of South Victoria. 



Very early in the Tertiary Period, or soon after the 

 polyprotodonts had reached the future Euronotian Region, 

 variations arose in certain of the forms and the earUest 

 diprotodonts were gradually developed. There is, I think, 

 clear evidence that these appeared first in the Euronotian 

 Region — probably in its sub-tropical parts — and spread 

 thence northwards, southwards and then westwards. Pro- 

 fessor Tate has pointed out that at the close of the Cretaceous 

 Period physiographical changes occurred resulting in the 

 production at one time or another of barriers to migration to- 

 wards the west. Central Australia, previously covered by the 

 Cretaceous sea was now dry and possibly desert land offering a 

 cHmatic barrier ; to the south of this lacustrine beds indicate 

 the existence in Pliocene times of a great lacustrine area 

 centering round Lake Eyre and probably extending over 

 what is now the Murray Desert and the Riverina ; whilst 

 further south again marine tertiary deposits indicate a con- 

 siderable submergence of the south and south-eastern parts 



