34 AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 



the wind. The main body, however, sweeps along the western 

 side of the plateau, turning* sharply and with increased velocity to 

 the east round S.W. Cape at the south-west corner of Tasmania. 

 These are the conditions that have existed since the formation of 

 Bass Strait, but before that, the whole volume of the current was 

 diverted south-easterly along the western side of the plateau — the 

 pre-Yolandean shoreline. The south-east corner of the mainland 

 did not experience the climatic influence of that portion that 

 now passes through Bass Strait, which, considering the tempera- 

 ture of the Southern Ocean Current is less than 62° F., must have 

 been appreciable. 



II. Rainfall: Fertility and Aridity. 



The present rainfall-reliability belt is shown in Fig. 1; it is 

 substantially that shown by Taylor (1920, Fig. 125). It extends 

 from west to east across southern Australia to the Dividing Range, 

 and north, for the most part, along the western slopes of the 

 range into Queensland. The arid belt terminates against its 

 western boundary and the reliable rainfall belt extends some 

 250 miles north of the line of maximum aridity (Fig. 1). Falling 

 for the most part on the western slopes of the Dividing Range, 

 the reliable rainfall is closely connected with the Antarctic lows 

 travelling from west to east and is obviously mainly orographic. 



The rainfall of the coastal corridor between the Dividing Range 

 and the east coast, other than the cyclonic rain, comes mostly 

 with the trade-winds that extend furthermost south in the sum- 

 mer months. The rainfall of the north portion of the corridor is 

 seasonal. The corridor has always had a useful, if uneven, rain- 

 fall, particularly that part of it south of the Tropic of Capricorn ; 

 the number of permanent coastal streams draining is evidence 

 of this. It connects northern Australia with south-east and 

 southern Australia by a fertile belt — a fact plainly evident in the 

 distribution of the white population. 



During the last glacial period, the reliable rainfall extended 

 along the western slopes of the Dividing Range to the Atherton 

 Plateau in North Queensland (Fig. 13) ; this was the period of 

 the greatest and most extensive fertility for eastern Australia. 

 The rainfall-reliability belt receded slowly southwards until the 

 Postglacial Optimum, but has since been moving northwards. 



Such streams as the Diamantina and the Georgina flowing south 

 had their sources in the extension eastwards of the Selwyn 

 Highlands, a low physiographical divide that, owing to its trend, 



