47 



DESCRIPTION OF A DISTURBED AREA OF CAINOZOIC ROCKS 

 IN SOUTH AUSTRALIA, WITH REMARKS ON ITS GEO- 

 LOGICAL SIGNIFICANCE. 



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

 Palaeontology in the University of Adelaide. 



[Read April 4, 1911.] 



Plates X. to XIX. 



Contents. Page. 



Introduction ... ... ... ... ... ... ... 47 



Description of Cainozoic Beds in Disturbed Area ... 49 



Tectonic Considerations ... ... ... ... ... 53 



Geological Age of the Earth Movements 56 



Introduction. 



Marine limestones of Lower Cainozoic age occupy nearly 

 the whole of the maritime districts of this State, extending on 

 the westward into Western Australia, and on the eastward into 

 Victoria. The submerged regions at the time when these lime- 

 stones were laid down included the sites of the three southern 

 capitals of Australia, viz., Perth, Adelaide, and Melbourne. 

 The two important gulfs of South Australia, at that time, 

 were troughs in the open ocean ; and Kangaroo Island, Yorke 

 Peninsula, and much of Eyre Peninsula, were sunken reefs 

 in the sea; a wide gulf occupied the Murray Plains, and 

 extended northward into western New South Wales. 



Since this period of maximum depression of the southern 

 coastline, there has been an elevation of the land and the 

 sea has retired from its former bed to an extent that has 

 left, at least, 200 ft., in vertical height, dry land. This 

 elevated sea floor has been subjected to various vicissitudes. 

 Active volcanoes have broken through its deposits and spread 

 out sheets of lava and other volcanic material, thousands of 

 square miles in the South-East of this State were again sub- 

 merged, and the older Cainozoic rocks became covered by 

 newer marine deposits. Exposed to atmospheric waste through 

 long ages these beds have been deeply eroded, lithologically 

 transformed, and, in many instances, reduced to small and 

 isolated fragments. 



The age of the beds in question, according to the late 

 Professor Ralph Tate and Mr. J. Dennant, based on the 

 percentage of living species which they contain, is Lower 

 Cainozoic, or the equivalents of the Eocene beds of the 



