74 



Remarks. 



It is an interesting point to consider whether- the Kan- 

 garoo Island outflow was synchronous with the volcanic 

 eruptions in the south-eastern portion of South Australia. 

 The basalt occurring in the Mount. Gambler district is, how- 

 ever, of late tertiary or pleistocene age. The rock is, for the 

 most part, very little decomposed. The fragments of basalt 

 and lherzolite which occur in the ash -beds overlying the basalt 

 are exceptionally fresh ,(?? and as far as I can ascertain there 

 are no instances where valleys have been cut through this 

 basalt, or capping hills, as is the case on Kangaroo Island. 



Returning to the Kangaroo Island occurrence, we find 

 that a great deal of denudation and weathering has gone 

 on. The basalt, which is probably contemporaneous, has been 

 cut through by valleys. It also caps the hills in the vicinity 

 of Wisanger, and occupies an eroded valley near Kingscote 

 about 100 ft. above sea-level. The rock itself is decomposed 

 to a greater extent than the Mount Gambier type. Instead 

 of being, for the most part, an olivine-basalt, it is an enstatite- 

 basalt, although an olivine-basalt has been described by Dr. 

 Chewings and Mr. J. C. Moulden. The evidences of weather- 

 ing are particularly marked in the quarries at the Stone Jetty 

 and the Bluff, where columnar jointing is developed to a 

 great extent, thus causing the rock to break up easily with 

 the aid of a pick. Personally, I do not think that the 

 Kangaroo Island basalt was synchronous with the occurrence 

 in the South-East, but, from the above considerations, believe 

 it to be a tertiary outflow earlier than the Mount Gambier 

 type. 



Acknowledgments. 



In conclusion, I desire to extend my thanks to Dr. Maw- 

 son and Dr. Cooke for the interest they have shown in the 

 preparation of this paper. 



University of Adelaide. 



EXPLANATION OF PLATE XX. 



Fig. 1. Phenocrysts of atjgite and enstatite, containing 

 tabulae of microlitic plagioclase. (x25) Crossed nicols. 



Fig. 2. Phenocryst op labradorite, showing zonal struc- 

 ture, and inclusions of base. (x!8) Crossed nicols. 



W Trans. Uoy. Soc, S.A., pree. vol. Analysis of Lherzolite. 



