166 president's address. — section c. 



graben, of the Gulf. This north and south subsidence created a trans- 

 verse system of drainage that intersected the longitudinal valleys and 

 diverted their drainage. 



The rivers of the Mount Lofty Ranges stand related to an extensive 

 field of phenomena that indicate important modifications of the surface 

 features during Pleistocene times. 



Dating from the earlier cainozoic, and for a time during the 

 Neogene uplift, the drainage of south-central Australia found its 

 outlet on the southern coast. The central basin of Australia, if it 

 existed at all at that time, was of limited extent, and was situated 

 further to the north than the present Lake Eyre depression. The 

 trunk rivers flowed north and south, running parallel with the prevailing 

 strike, and formed main arteries of drainage, of which only the River 

 Murray has persisted to the present day. Two other important outlets 

 for the northern drainage certainly existed, the lower reaches of which 

 are represented by the drowned valleys of the two great gulfs. Captain 

 Flinders, with the instinct of a true geographer, expected to find a large 

 river at the head of each of these two considerable inlets of the sea, 

 but was disappointed, and very much surprised at their absence. In 

 describing the head of Spencer Gulf, he says, " The width of the opening 

 round Point Lowly left us a consolatory hope that it (Spencer Gulf) 

 would terminate in a river of importance, . . . the inlet wholly 

 terminated ... it seemed remarkable, and was very mortifying 

 to find the water at the head of the gulf as salt nearly as at the ship." * 

 Of the head of Gulf St. Vincent he says, " The shores then appeared to 

 close round at the distance of 7 or 8 miles, and the absence of tide gave 

 no prospect of finding any river at the head of the inlet." f A 

 forecast that was soon verified by a closer examination in a boat. 



When the epeirogenic uplift had reached its maximum, and a re- 

 verse movement had begun, the South Australian plateau broke up 

 into large blocks, with a meridional rift valleyj that extended from 

 the south coast to the north end of Lake Torrens. As a concomitant 

 of these earth movements a vast regional senkungsfeld, or sagging of 

 the earth's crust, occurred in Central Australia, which profoimdly 

 influenced the physical and climatic conditions of South Australia. 



* Flinders' " Terra Australis," pp. 15&-158. 



t Loc. cit., p. 177. 



X Professor J. W. Gregory was the first to apply this term to the great sunken area of the 

 Qulfg. [Dead Heart of Australia, pp. 149-150.] He, however, appUes the term to Spencer Gulf, 

 as the southerly and submerged portion of the rift-valley. For reasons stated above we have 

 not hicluded Spencer Gulf in the main line of fracture — although the aUgnmentot that Gulf accords 

 very well with that of Lake Torrens, and may be included, to some extent, fn the same system 

 of fractures. At present we have no definite evidence of this, other than accordance with similar 

 physiographical features and the fault scarp of its northern end ; but in the case of Gulf St 

 Vincent, there are the clearest evidencos of trough-faulting. Following north, from the head 

 of ihie ^f, the " rift " probably crosses the northern portion of Yorke Peninsula, and is marked 

 by the important fault-scarp, facing the sea, from Port Pirie to Port Augusta, and from thence 

 up the western face of the northern Flinders Ranges. 



