192 THE BUILDING OF EASTERN AUSTRALIA 



The faulting down of Bass Strait saved a remnant 

 of the original inhabitants of Australia (the Tasmanian 

 aborigines) from utter destruction by the invading 

 Australian aborigines. 



Torres Strait was probably also formed during the 

 occupancy of Australia by the blacks. 



Stream Directions. 



Great changes in the drainage systems of Australia, 

 resulted from the Pliocene uplift. Andrews has shown 

 that some streams cut down rapidly enough to keep pace 

 with the uplift. He quotes the Hawkesbury River as an 

 instance. Othei rivers were diverted from their courses. 



The parallelism of many rivers with the coast has 

 given rise to much controversy and speculation. Hedley 

 [19 and 20] sees in it evidence of a great fold rolling in on 

 Australia from the Pacific. Andrews is inclined rather 

 to consider these remarkable streams due to faulting. 



[30] Woolnough and Taylor have suggested that the 

 Hawkesbury (Wollondilly) formerly tapped the Shoalhaven, 

 Tuross and other south-coast rivers. But this great 

 Wollondilly river was beheaded by coastal streams which 

 were rapidly cutting back in a westerly direction. These 

 streams having a steep fall to the sea carved canons rapidly, 

 whereas the sluggish Wollondilly cut down but slowly> 

 and fell an easy prey to piracy. 



The writer [13] has shown that the Upper Mary River 

 (rising in the Conandale and Yabba Ranges), Queensland^ 

 was once part of the Maroochy River, flowing through the 

 Eumundi Gap, in the Blackall Range. Here, undoubtedly, 

 the uplift of the coastal plain of East Moreton has tended 

 to aid a capture of consequent by subsequent streams. 



In New South Wales, where the reverse has taken 

 place, we must look for a different cause for the parallelism 

 of the early streams with the coast. To the writer, the 

 most reasonable explanation seems as follows : — The 

 elevation of the Miocene peneplain carved in Permo- Carbon- 

 iferous and Mesozoic sandstone gave rise to the production 

 of cracks and joints in the sandstone. The major lines 

 of weakness thus formed followed the structural directions 

 of the subjacent old rocks. Master joints in the sand- 

 stones clo&^ely followed fault lires, anticlinal axes and similar 

 structural lines of the older rocks. Along such cracks 



