138 



ties to the Houghton magma rocks, e.g., the felspar porphyry 

 of the Jamestown erratic, containing acid plagioclase and 

 diopside, and the acid plagioclase and titaniferous magnetite 

 of the Olary aplites, and other rocks in that localit}^ In an 

 Appendix to this paper a list of certain other rocks is givefi. 

 similar in some ways to the Houghton rocks. 



All this tends to show the truth of the thesis outlined 

 in the Introduction, namely, that so widespread are the rocks 

 of this type throughout South Australia that the State may 

 be considered as a petrographical province, the characteristic 

 featiire of which is the high percentage of titanium acid, to 

 a less degree the abundance of soda. At present our know- 

 ledge of South Australian petrology is insufficient to show 

 whether later igneous intrusions are so markedly titaniferous 

 as the Pre-Cambrian or early Palaeozoic derivatives of the 

 Houghton magma. The igneous rocks of earlier date than 

 these were certainly also titaniferous, for rutile and ilmenite 

 are joresent in unusual amount in the Algonkian schists de- 

 rived from them by denudation and sedimentation. Th& 

 ilmenite in Cambrian ilmenite grits was derived from the 

 denuded Houghton magma intrusions. 



It is perhaps noteworthy in this connection that high 

 titanium content is a dominant feature of the rocks of the 

 alkaline province of Eastern Australia. ^22) 



A CKNOWLEDGMENTS. 



I desire to express my warmest thanks to Mr. W. How- 

 chin, F.G.S., for the interest he has shown in the progress 

 of this work, and the great assistance he has rendered me on 

 every occasion in giving me most useful local geological in- 

 formation. I am deeply indebted, also, to Professor Rennie 

 for allowing me to have the use of his private laboratory, 

 apparatus, and chemicals for rock analysis ; and to both Pro- 

 fessor Rennie and Dr. W. T. Cooke for much advice and 

 assistance. Dr. W. G. Woolnough has been kind enough to 

 examine several of my slides and to give me the benefit of 

 his opinion thereon. 



Postscript, added October, 1909. 

 While the foregoing was passing through the press I re- 

 ceived from Mr. Howchin a specimen of an intrusive into the 

 Pre-Cambrian rocks at Mount Compass, some fifteen miles 

 north-east of Yankalilla. Mr. Howchin states that the rock 

 is associated with a large ilmenite vein, about a quarter of 

 a mile long. The rock is clearly a product of the Houghton 



f22)H. I. Jensen, D.Sc, Proc. Linn. Soc, N.S.W., 1908, 

 p. 601. 



