268 



Notes on the Geological Features of 

 Southern Yorke Peninsula, 



By T. C. GrREENWAY, B.Sc, AND H. Tarlton Phillipps. 

 Commumcated by Walter Howchin, F.G.S. 



[Read October 21, 1902.] 



Plate VII. 



Tlie late Professor Tate, in a paper read before this Society 

 in 1889, on tke Botanical Featiu'es of Southern Yorke 

 Peninsula., gave a brief introductory sket<;h of the geology of 

 the district, in which the Pleistocene deposits, Eoceue lime- 

 stones, and Ai'chsean rocks were briefly described, and the 

 recent elevation of the land, which lead to the existence of a 

 "deserted seaway,' in the Great Salt Marsh, were noted. 



In 1900 Mr. Walter Howchin, F.G.S., read a paper on 

 Evidences of Extinct Glacial Action in Southern Yorke 

 Peninsula, in which it was shown that the glacial till beds 

 formed the dominant geological features of the district, and 

 occupied a stratigraphical position inferior to the Eocene lime- 

 stones. The same author, a few months later, in a second paper, 

 advanced the theory that the ''salt lagoons" of the southern 

 portions of the Peninsula (outside the area of raised beaches) 

 were not of marine origin, but were the result of (a) the re- 

 moval of the gi'eater part of the lower Tertiary limestones by 

 chemical solution ; (b) the upper surface of the glacial clay 

 forming a retentive floor ; and (c) that the secondary deposits 

 of travertine and saline substances were the reconstructed 

 equivalents of the removed limestones. 



It has thus been shown by the last-named author that these 

 lagoons of the Peninsula must be divided into two classes with 

 reference to their origin : (1) The salt lagoons produced by the 

 removal of the Tertiary bads by solution ; (2) raised beaches. 



Since those belonging to class 1 occupy depressions in the 

 sui'face of the glacial clay, which underlies practically the whole 

 of the southern portion of the Peninsula, they are of consider- 

 able geological importance as indicating those districts w^here 

 the glacial clay approaches the surface. Outside these ai'eas 

 we may, therefore, conclude that the glacial clay underlies 

 porous beds, which do not allow the water to accumulate. The 



