36 AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 



the effect of raising the mean annual temperature. The increased 

 temperature prevented rain falling on the advanced side of a 

 barometric depression and limited it to the departing quadrant. 

 These, he maintained, are the typical conditions of the rainfall 

 of South Australia at the present time. He also attributes aridity 

 to physiographical changes, but the writer has reason to believe 

 that his conclusions are not supported by current research. 



In the Lake Eyre Basin, the sub-surface deposits contain the 

 remains of Viprotodon, crocodiles, chelonians and other forms 

 implying wetter, moister conditions. The surface deposits 

 accumulated during the warmer period of the Postglacial 

 Optimum and have been transported thither by the spasmodic 

 drainage accompanying convectional and seasonal tropical 

 rainfall ; the sub-surface deposits were deposited during the earlier 

 part of the Postglacial or the last glacial period. 



The effect of the hot period of the Postglacial Optimum is seen 

 in the forests of eastern Australia. Taylor (1920) observes that 

 many plants require rainfall all through the year, a break of a 

 month or two being deleterious; this applies especially to the 

 tropical forest element present along the east coast and south-east 

 coast of Australia. He found that the 12 isopleth, which bounds 

 on the west, the region receiving at least an inch of rain each 

 month of the twelve, does not coincide with the limits of the 

 thick tropical or temperate forest, so he plotted the line bounding 

 the region where an additional inch fell during each of seven 

 months on the regions of considerable rainfall. This was found 

 to agree closely with the distribution of both the tropical and 

 temperate forest. In this area, the rainfall practically equals 

 evaporation and the required rainfall seems to be largely a 

 matter of elevation ; evaporation is a much more potent factor on 

 the lowlands west of the highlands of eastern Australia than on the 

 highlands themselves. During the warm period of the Postglacial 

 Optimum the forests must have been much more restricted than 

 they are today. 



Southwards of the arid belt is the Mediterranean type of climate 

 with an increased winter rainfall, but hot, generally rainless 

 summers ; this type passes into the temperate rain-belt. South of 

 this is the boreal belt in which a terrestrial region is character- 

 ized by an ample coastal rainfall, but usually a dry interior ; the 

 winter is severe with a persistent snow cover and the summer is 

 short. Evidence of it in Australia during the glacial period is 

 seen in the peat deposits in southern Victoria and Tasmania; 

 peat formation calls for a rainfall of at least 40 inches and a 

 mean temperature above 40°F. 



