president's address. — SECTION c. 165 



St. Vincent. The beds in question occur as thin cappings on Kangaroo 

 Island and in southern Yorke Peninsula, and for the most part resting 

 on a floor of Permo-carboniferous glacial clay. This clay is also on the 

 coast at Cape Jervis, thus forming, with Kangaroo Island and Yorke 

 Peninsula, an investing circle around the outlet of the gulf, while, at 

 Kingscote, on the north side of Kangaroo Island, the same glacial clay 

 has been proved to continue downwards, from sea-level to 1,100 feet, 

 where it rests on Cambrian slates. It is somewhat anomalous that 

 there should be such a great thickness of marine cainozoic beds in the 

 trough near Adelaide, while they appear to be entirely absent below 

 sea-level at the entrance to the Gulf. They may, of course, be faulted 

 down in a narrow strip in the centre of Investigator Strait. In any 

 case, Kangaroo Island and Yorke Peninsula form horsts that, at 

 present, are but little above sea-level. 



We must now take another step forward and study the course of 

 events that immediately preceded the present outlines in South Aus- 

 tralian topography. Or, in other words, 



THE CHANGES THAT TRANSPIRED IN THE PLEISTOCENE 



PERIOD. 



This forms one of the most interesting chapters in South AustraUan 

 geology, for it throws some light on the causes of existing earth-forms, 

 the origin of the existing system of drainage, and the physiographical 

 changes that brought in the present arid conditions in the climate of 

 the country. It is the rivers, chiefly, that must tell us this story — 

 rivers that are now dead — antecedent rivers — young rivers— reju- 

 venated rivers — rivers partly old and partly young — lost watersheds — 

 new water partings. 



If we examine the topographic features of South Australia we 

 must be struck by the fact that neither the rivers nor the watersheds 

 conform to the natural grain of the country. The strike of the Cam- 

 brian beds is approximately north and south — the hard rocks form the 

 elevated features and the soft rocks the intervening valleys — but. 

 while these longitudinal valleys are choked with old fluviatile material, 

 the existing rivers that find their way to the Southern Ocean are all 

 transverse rivers. This is true of the"^Broughton, the Light, the North 

 Para, the South Para, the Little Para, the Torrens, and the Onka- 

 paringa (in part) ; all of which cut the ranges at right angles, and must 

 be regarded as consequent rivers that were called into existence by the 

 general uplift of the country and its concomitants. That these rivers 

 should not flow southward, instead of westward, is the more remarkable, 

 inasmuch as the valleys trend in that direction. The orientation of 

 these rivers — at right angles to the older system of drainage- was 

 probably brought about by the development of the trough-fault, or 



