79 



Concluding Remarks. 



In the observations now detailed a very large area has been 

 .added to the known extent of the extinct glacial field of 

 South Australia. The glacial outline has not only been car- 

 ried across Gulf St. Vincent, but it is clear that practically 

 the whole of the southern portion of Yorke's Peninsula, mea- 

 suring, roughly, forty miles by twenty miles, has been at 

 one time under glacial conditions. This conclusion has been 

 forced upon me from the widely distributed proofs of ict; 

 action on the northern and southern coasts as well as through- 

 out the inland districts. With the exception of a few out- 

 liers of Eocene limestone and some superficial deposits, the 

 geology of the inland country is of a uniform character, and 

 can be summed up in one great clay formation — the glacial 

 clay. A unique feature of the district is the abundance of 

 salt lagoons, of which there are no less than 200 recorded on 

 the official maps within the area under consideration. There 

 can be little doubt that the glacial clay underlies these 

 lagoons and imparts to them the retentive quality, so that 

 these saucer-shaped depressions, receiving the drainage of the 

 country, play the part of evaporating pans and concentrate 

 its salts. The waste of this clay along the banks of the 

 lagoons leads to the exposure of the erratics belonging to the 

 formation, some of which have been noted in this paper. 



Another important datum line has been supplied by these 

 observations bearing on the age of the glacial cold in these 

 latitudes. At Hallet's Cove, on the opposite side of the 

 Gulf, the evidence shows that the glacial deposits were laid 

 down in pre-Miocene times. In southern Yorke's Peninsula 

 the geological age of these deposits has been thrown back yet 

 one more step through their occupying a stratigraphical posi- 

 tion inferior to the Lower Tertiary. There is, moreover, 

 clear proof of stratigraphical unconformability in the eroded* 

 surface of the glacial clay on which the marine beds of the 

 Older Tertiary rest. It is, therefore, I think, clear that the 

 glaciation must be referred to pre-Tertiary times, and cannot 

 be newer than a Cretaceous or Cretaceo-Eocene age. 



The discovery of glacial clay inferior to the Eocene beds at 

 Troubridge Hill and Point Turton will contribute to the 

 correlation of beds of a similar character in other parts of the 

 colony. On the north side of the mouth of the Onka- 



* At Corney Point, where, the metair »rphic rocks rise above sea level, 

 there is a thin layer of Eocene limestone in a limited patch resting upon 

 the primary rocks. The glacial clay is absent. At this elevation it may 

 have been originally a thin deposit, and therefore easily denuded before the 

 bedrock sunk below the level of the Eocene sea. 



