176 president's address. — section c' 



took shape. We now know, on such evidences as have 

 been briefly outlined in this address, that the existing 

 hills are comparatively recent in their origin, and have 

 been the result of epeirogenic rather than orogenic move- 

 ments. This modern period of uplift in South Australia 

 probably coincided, in the main, with similar movements 

 in eastern Australia, which Mr. E. C. Andrews suggests 

 should be called the Kosciusko Period.* The associated 

 phenomena, in both the geographical areas, possess 

 much in common, and there is a corresponding evidence 

 of the juvenility of the erosion features in each case. 



2. The two important inlets of the sea, known as Spencer 

 Gulf and Gulf St. Vincent, are also of very recent origin, 

 and owe their existence to earth movements which are 

 probably still in progress. In Post-Pliocene times the 

 land stood at a greater elevation than it does to-day. 

 The river systems were highly developed, radial in 

 structure, and continental in extent. The present 

 drowned valleys of the gulfs formed dry land — or, rather, 

 were extensive flood-plains built up by the fluviatile 

 sediments brought down from the interior of the conti- 

 nent. A bore put down at Port Wakefield, near the head 

 of Gulf St. Vincent, went through 310 feet of various 

 coloured sands, gravels, clays, and carbonaceous materials 

 before reaching Cambrian bed-rock. The Dry Creek bore, 

 only a few feet above sea -level and within little more than 

 a mile from the Cambrian outcrops of the ranges, went 

 through 320 feet of similar alluvial deposits, and then 

 touched the fossiliferous Pliocene. The Croydon bore, 

 at 56 feet above sea-level, went through 395 feet of allu- 

 vium, also resting on the fossiliferous Pliocene. The 

 present Gulf is very shallow. In many places fluviatile 

 beds of the Adelaide Plains are seen to pass below low- 

 water mark. The piles that support the lighthouse on 

 Wonga Shoal, opposite the Semaphore, were driven into 

 freshwater clays to a depth of 22 feet. 



From the facts just stated the land in the %dcinity 

 of Adelaide must have experienced an elevation of not 

 less than 300 feet, following the retreat of the Pliocene 

 sea ; and, later, there must have been a corresponding 

 lowering of the land level to permit of the sea's return to 

 the region of the Gulf. The extent of this last submer- 



• " Geographical Unity of Eastern Australia." Roy. Soc. New South Wales, Vol. XLIV, 

 p. 426. 



