14 



On an outlier of Older Cainozoic Rocks in the 

 River Light near Mallala. 



By Walter Howchin, F.G.S., Lecturer in Geology and 

 Palaeontology, University of Adelaide. 



[Read April 11, 1912.] 



Plate I. 



The distribution of the older Cainozoic rocks in South 

 Australia is such as to suggest that, at one time, there was a 

 continuous sheet of these beds over the maritime districts, 

 including much of the highlands, and extending inland to an 

 unknown distance. The occurrence of these marine fossili- 

 ferous rocks in their present positions give proof of a former 

 lower level of the land which allowed an epicontinental ex- 

 tension of the sea margins. They also tell of a subsequent 

 elevation of the land, including the submerged continental 

 shelf, amounting to many hundreds of feet, which made of 

 South Australia an upland plateau. These elevatory move- 

 ments exposed the marine sediments to severe weathering 

 and erosion, by which they have been entirely denuded from 

 large areas that they once occupied. 



It is only in the extreme western and eastern sides of 

 the southern portion of South Australia that the older 

 Cainozoic rocks have been preserved in extensive sheets — the 

 one occupying the head of the Great Australian Bight and 

 extending inland for a distance of, at least, 150 miles; the 

 other includes the Murray Plains (extending northwards into 

 New South Wales) and the South-East to the Victorian 

 borders. Between these extreme localities, where the main 

 outcrops occur, crust movements of great importance have 

 transpired, which have broken up and removed the greater 

 part of the beds referred to, leaving only isolated fragments 

 as outliers of the main formation, some of which are so small 

 that they would not yield sufficient material to make a good 

 quarry. Of these outlying fragments the following groups 

 may be indicated : — 



1. In southern Yorke Peninsula, resting on glacial clay 

 of Permo-Carbonif'erous age : — Outcrops occur in the neigh- 

 bourhood of Troubridge, on the south coast ; along the 

 south-eastern coast, from Edithburgh to near Black Point ; 

 Point Turton, Hardwicke Bay ; and several inland patches. 



