AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 31 



retreat to its former state. Tims the line of maximum aridity 

 during the glacial period was approximately 200 miles south of 

 Darwin, but at the Postglacial Optimum 400 miles north of 

 Adelaide. (Fig. 2). 



During the glacial period, only the higher altitudes of Australia 

 were beset with glacial conditions — the Margaret glaciation — 

 which were too restricted to affect to any extent the climate: any 

 reference here to glacial or intcrglacial in connection with the 

 mainland refers only to the periods when those stages prevailed 

 in other latitudes. The following were the climatic, and hence 

 the physical extremes, in the Australian region during the 

 Quaternary : 



Postglacial and inter- Glacial Period. 



glacial Periods. 



New Guinea. Tropical rain-forest. Savannah. 



Northern Australia. Savannah and tropical Arid belt. 



rain-forest. 



Lake Eyre Basin. Arid belt. Steppe. 



South-cast Australia. Steppe. Temperate rain- 

 forest, 



Tasmania. Temperate. Glaciated. 



The south-east, the coastal corridor, the orographic rainfall- 

 belt and the extreme south-west of Australia have always been 

 regions that have been more or less fertile ; the rest of it has been 

 at some time successively desert or on the borderline of complete 

 aridity, savannah, steppe, or partly in the fertile belt. In Europe, 

 the continental character of the climate during the retreat of the 

 ice-sheet that ushered in the dry period, although largely in- 

 fluenced by geographical distribution, was, to some extent, due 

 to astronomical causes, and assuredly had its equivalent in the 

 Southern Hemisphere. It concluded about 4,000 B.C., when 

 there was a period of submergence — the Atlantic stage. The 

 Postglacial Optimum is placed here ahout 2,000 B.C. — i.e., 4,000 

 years ago (cf. Brooks, 1922). A progressive change of climate 

 leading to the Postglacial Optimum has been assumed, although, 

 doubtless, there have been minor climatic fluctuations; the small 

 amount of geographical change that has occurred in Australia in 

 the Postglacial — it has occurred mainly in the north — has probably 

 made these less marked and infrequent. Glaciation ended in 

 lowland Europe about 7,000 years ago, but the climate became 

 appreciably warmer about 8,000 years ago. 



Glaciation on the Australian mainland was restricted during 

 the last glacial period to a small area on Mt. Kosciusko. In Tas- 



