276 



between Hillock Point and Point Yorke for about five miles. 

 These mainly consist of gneiss, more or less granitoid, charac- 

 terised by numerous veins of quartz a,nd felspar. The gneiss 

 is usually coarsely crystalline, the folia being very clearly de- 

 fined, while the granite is mainly reddish in color, and con- 

 tains numerous a^id segi*egations. 



The .principal feature of this locality is a large dyke of 

 diorite. In the neighborhood of this the gneiss is contorted 

 to a remarkable degree, masses of biotite, exceeding 2 ft. in 

 thickness, being developed in the vicinity of some of the dykes 

 as a result of contact metamorphism, the biotite in many cases 

 passing first into an a.ugen gneiss, and then into a true granite 

 or gneiss at a short distance from the dyke. These dykes 

 of dolorite and diorite respectively are of special interest as 

 being the only known occurrences of unaltered basic eruptive 

 rocks in southern Yorke Peninsula. 



Conclusion. 



Additional evidence in favor of Mr. W. Howchins theory 

 as to the origin of the salt lagoons in the neighborhood of 

 Yorketown is furnished by the fact that these seem to be con- 

 fined entirely to the district where the glacial clay outcrops, 

 and since we find beds of Tertiary limestone on either side of 

 this district, we may, therefore, infer that the intermediate 

 deposits have been removed by solution as he suggests. Fur- 

 thermore, at Point Turton, where the polyzoal limestone is 

 exposed m the cliff face, we have unmistakable evidence of its 

 replacement by travertine, which attains a thickness of from 

 15 to 16 ft., and in some cases penetrates nearly to the base 

 of the formation. Outside this lake area we find numerous 

 salt lagoons and marshes, which, however, not only differ in a 

 very marked manner from the former in their physical charac- 

 teristics, but also present unmistakable evidence of their 

 marine origin in numerous exfoliating shell banks. 



A glance at the sketch section from Corney Point to Edith- 

 burg will show that the glacial till was laid down in an 

 eroded hollow in the Archcean rocks, which increases in depth 

 towards the east, the principal Eocene deposits occupying an 

 analogous position with regard to the glacial clay, while the 

 Miocene beds were likewise deposited in a hollow on the east 

 side of the Eocene. The striking similarity existing between 

 these three cases is suggestive of a common agent of erosion, 

 though possibly the erosion of the Archseanrocksmay have been 

 brought about by a glacier flowing along a depression bounded 



