74 



AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 



mum, while during the greater part of the Postglacial, it slowly 

 moved southwards and contracted to its minimum at the Post- 

 glacial Optimum. The fertility of eastern Australia has been 

 influenced by the fact that the Great Dividing Range skirts its 

 eastern coastline and is responsible for the coastal corridor and 

 the orographic rainfall belt; on the other hand, the fertility of 

 the coastal belt of western Australia has been complicated by 

 conditions not found in the east. 



In connection with migration, climatic conditions are discussed 

 25,000 years ago during the glacial period; 15,000 years ago or 

 thereabouts when the tropical rain-forest advanced into the Cape 

 York Peninsula; 8,000 years ago when Torres Strait separated 

 New Guinea from the mainland, and 4,000 years ago at the Post- 

 glacial Optimum. The fertile tracts at these times are best con- 

 sidered by grouping the rivers into basins in respect to the 

 sources, intake, and outlets of the drainage channels of the con- 

 tracting rainfall-reliability belt and the advance southwards of 

 the arid belt. This grouping is tabulated. 



Basins 



Rivers 



Source 



Outlet 



Rainfall 



I Carpentaria Roper, McArthur, Selwyn High- Gulf of Carpen- 



(western part) Gregory, Lcich- lands taria. 

 hardt, Clon- 

 icurry. 



II Carpentaria Mitchell, Gilbert, Great Dividing Gulf of Carpen- 



( eastern part) Flinders. Range taria. 



III Diamantina 



IV Cooper 

 V Darling 



VI Murray 



Diamantina, 

 Georgina, Hay. 



Cooper, Thom- 

 son, Barcoo. 



Darling, Barwon, 

 Paroo, Warrego, 

 Condamine, 

 Macintyre, 

 Gwydir, Namoi, 

 Castlereagh, 

 Macquarie, 

 Bogan. 



Murray, Lachlan, 

 Murrumbidgee, 

 Goulburn. 



Selwyn High- Lake Eyre 

 lands, Macdon- 

 nell Ranges 



Great Dividing Lake Eyre 



Range 

 Great Dividing Murray River 



Range 



Tropical 



Tropical 



orographic, 



monsoonal. 



Tropical 



Tropical 

 orographic 



Orographic 



Great Dividing Southern Ocean 

 Range 



Orographic 



In the glacial period, the rainfall-reliability belt extended on 

 the west side of the Main Coast Range as far north as the Ather- 

 ton Plateau, and west from the Great Dividing Range beyond 

 Lake Eyre covering most of the Diamantina Basin (III) and the 

 Cooper Basin (IV) ; west of it to the western coastal belt. Central 

 Australia and a large part of Western Australia was in the arid 

 belt and steppe region. The whole of south-eastern Australia, 



