283 



with polar extremities. The outcrop extends for about eight chains (Mawson, 

 1907). 



Lower Pliocene Rocks in Section A. 



The fossiliferous Lower PHocene beds probably at one time formed a con- 

 tinuous deposit resting on the older rocks that occupied the area of the present 

 Gulf and its margins. They are now found only in isolated patches, one of the 

 largest of these comprises the flat knoll on which Adelaide is built. Formerly, 

 they were exposed on the banks of the Torrens (where the engine houses have 

 been constructed) and also in quarries that were worked behind Government 

 House. 



The first appearance of the Lower Pliocene beds on the coast is in a small 

 washout, situated directly westward of Marino railway station, where a fossili- 

 ferous sandstone of this age forms the lip of a waterfall. It occurs near the 

 extreme northerly limits of the Cambrian outcrops of the neighbourhood, and is 

 exposed to the extent of only a few square yards. The bed is, for the most 

 part, a breccia, resting on the edges of Cambrian grits that have a dip of 80° to 

 the westward. Fossils are not very plentiful in the bed and are patchy in 

 their occurrence. The species determined are as follows : — 



Cominella subfilicea, Tate Diastoma provisi, Tate 



Natica suhvarians, Tate Montlivaltia variformis, Dennant 



Sandy patches occur, in places, on the top of the cliffs which may be 

 residuals of the Lower Pliocene, but no clearly defined deposits of this age are 

 found to the southward of the Marino outcrop till we come to the calcareous 

 plateau on the northern side of Hallett's Cove. Here the fossiliferous Lower 

 Pliocene beds rest on the glacial boulder clays, making a steep scarp, facing the 

 sea, and, together with the more recent beds, form a retreating cliff on the 

 top of the primary cliff consisting of Cambrian slates. 



The beds have been much leached of their lime content and the fossils occur, 

 mostly, as impressions and casts. Small nodules of Lithothamnion are moder- 

 ately common. The beds are thickest at their most northerly position, where 

 they form a scarp behind the principal exposure of the polished pavement, and 

 can be traced, inland, to a distance of about 200 yards from the sea-cliffs. 



Pleistocene Rocks in Section A. 



Mottled Sands and Clays. — These form the lowest of the three classes 

 of rock which occur, locally, as subsequent formations to the Pliocene. They 

 can be distinguished by their strongly mottled colouring, in patches of red and 

 grey, varying in composition from a tough plastic clay to that of an argillaceus 

 sand rock, and possessing considerable coherence by which they can maintain 

 vertical and wall-like faces though exposed to the weather. They make a 

 typical rock formation that is widely distributed, not only in the sections seen 

 on the coast, but in inland situations, and at various elevations. They occur on 

 both sides of the Gulf, making a very striking feature at Ardrossan, where they 

 form vertical sea-cliffs 40 feet in height (Howchin, 1918b). They are of fresh- 

 water origin and sometimes contain impressions of leaves. They are often 

 associated with the older river systems and are probably of Pleistocene age. 



Between Marino and Hallett's Cove these mottled sands and clays can be 

 seen, in many places, resting on the top of the purple slates and also in the rail- 

 way cuttings, where they are sometmes associated with indurated gravel beds. 



Recent Deposits in Section A. 



Reddish Clay. — The coastal plains and open valleys (especially those having 

 a north and south direction) usually carry a considerable thickness of alluvium. 



