170 president's address. — SECTION c. 



precipitous to a height of about 500 feet, and its full height is probably 

 not less than 1,200 feet. The bed of the river is narrow, but well 

 graded ; there are no waterfalls within its course, although several 

 of its tributaries show this evidence of their juvenility. In its upper 

 portions it has worked back into close proximity to the watershed of 

 the Onkaparinga and has pirated some of the head waters of that river. 



When the River Torrens leaves the Mount Lofty Ranges at the 

 mouth of its gorge and enters on the Adelaide Plains it crosses, in a 

 diagonal direction, an old meridional valley that once carried a river 

 of large dimensions. This old river came from the north, through the 

 Barossa country, via One-tree Hill, Golden Grove, Tea-tree Gully, 

 Highbury, and skirted the foot-hills of the Adelaide Plains. The 

 tilting of the lower Barossa earth-block appears to have led to the 

 creation of a series of lakes at the base of the Barossa scarp. These 

 lakes must have covered scores of square miles, and they led to the 

 deposition of tiie auriferous alluvial of the Barossa Gold-field. In 

 the neighbourhood of the mouth of the Torrens gorge, the old alluvial 

 sands and gravels are 3 miles wide, and on the Highbury side of the 

 valley these ancient river-terraces show a thickness of 250 feet. They 

 do not follow the valley of the River Torrens, in its westward extension, 

 but follow the scarp of the ranges, to the southward, forming terraces 

 along the base of the foot-hills, certainly as far as Burnside. 



In an earlier part of this address we saw that the Blackwood and 

 Belair platform carries important river deposits belonging to the 

 former north and south drainage. The beds just described as occurring 

 along the base of the foot-hills are precisely similar to those of the 

 Blackwood-Belair platform, but are situated about 500 feet lower, and 

 rest on a lower platform. There are three possible explanations of 

 these similar deposits at diverse levels, (a) That they were laid down 

 by distinct rivers of contemporary age. This is not probable, as it 

 is inconceivable that two great rivers could follow parallel courses, 

 close to each other, and at so great a difference in elevation. (6) That 

 they represent the same river at different stages of its history, the 

 deposits on the higher platform being the older, but the valley was 

 drained, and the river compelled to take a lower course, through parallel 

 faulting, in the development of the trough of the Gulf, (c) That the 

 deposits are of the same age and were laid down originally on the same 

 level ; the river was already dead when, by step-faulting, a portion 

 of the old river valley slipped down to its present position on the scarp 

 face. Of these three possible interpretations I think the last the most 

 probable. 



Next to the River Murray, the Onkaparinga is the most important, 

 as well as the most ancient, river basin in South Australia. The water- 

 shed of the Onkaparinga comprises 170 square miles, and exhibits some 

 remarkable features. In its head waters it has the characteristics 



