AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 35 



does not intercept orographical rainfall. These intermittent 

 watercourses, together with the south-west flowing Cooper, are 

 outlets to the Lake Eyre Basin at the present time of from 15 to 

 20 inches of mostly summer tropical rainfall falling on the 

 southern slopes of the Selwyn Highlands and on the western 

 slopes of the Dividing Range. The effects of climatic change and 

 the contraction of the rainfall-belt on these streams will be dis- 

 cussed under the heading Migration Routes (Part VIII). 



In the tropical rain-belt, in Australia, there is a rain-forest 

 comparable, as regards its ecology, with that in the Malay 

 Archipelago and the Malay Peninsula; it is restricted to its 

 northern part. The sub-tropical dry belt — the summer rain- 

 region of Australia, savannah and grassland — includes, at 

 present, a large portion of the north, south of the tropical rain- 

 belt. On the poleward sides of the latter, in both Hemispheres, 

 one passes into the arid belts, such as that in Central Australia, 

 with slight or no rainfall. It is difficult to gauge the aridity of 

 this in the past. At present the arid belt crosses Australia to 

 south-west Queensland and north-west New South Wales to the 

 edge of the rainfall-reliability belt ; as already noted, it does not 

 cross the latter into the coastal corridor. It includes the Lake 

 Eyre Basin that normally receives less than 5 inches of rainfall, 

 wholly convectional, but for periods of years no rainfall at all. 

 Heat and consequently evaporation are excessive, the former not 

 much less than the hottest parts of the Sahara (Kendrew, 1937), 

 yet scarcely any of its western portion is true desert and is not 

 as arid as some at the waterless west-coast deserts of other con- 

 tinents. Commenting on the desert-phase, Brooks (1926) states: 



In parts of the South American desert it lias probably not rained for 

 centuries. Such plants as there are show special devices to prevent the loss 

 of water, but in many deserts the ground is entirely bare of plants. Anions 

 animals, one of the most characteristic is the lung- fish (Ceratodus) , which is 

 adapted to breathe either air or water, and can remain dried up for long 

 periods. 



Ceratodus is still living in Australia and is significantly found 

 in what are now well-watered seasonal rainfall-tracts. 



The gibber plains of Australia attest long and recurrent periods 

 of aridity in the Quaternary. At the Postglacial Optimum the line 

 of maximum aridity was through Marree, about 50 miles south of 

 Lake Eyre, and the arid belt was then hotter and more arid. This 

 hot period which was world-wide ended about 2,000 years ago and 

 lasted about 4,000 years. Howchin (1913) believed the present 

 arid conditions of Central Australia had a gradual evolution and 

 were due to the sunkland in south Central Australia which had 



