56 



(2) The genetic relationships of the rocks are discussed, 

 and the conclusion is drawn that the first series was derived 

 by fractionation and sinking of crystals in an intercrustal 

 magma with subsequent intrusion at a higher level, while 

 the second series may have resulted from complementary 

 differentiation of a separate portion of the original magma. 



(3) The pneumatolytic phase of the intrusion is mani- 

 fested in : — 



(a) Quartz tourmaline nests in granites, aplites, etc. 

 (h) The greisenisation of the soda granophyres. 

 (c) The impregnation of the country rock in the neigh- 

 bourhood of the albite syenite. 



(4) From comparison with similar occurrences elsewhere 

 in the State it is considered probable that a magma underlay 

 much of South Australia, as well as the Barrier region of 

 New South Wales, in paulo-post-Cambrian times, intrusion 

 of which was expressed either by granites and allied rocks 

 or by dyke intrusions of both basic and acid types. 



(5) The age of the intrusions is discussed, and Tilley's 

 view of their connection with the folding of the Cambrian 

 rocks is upheld. 



(6) The contact metamorphism produced by the intru- 

 sions is dealt with and a number of rock types are described. 



IX. Acknowledgements. 



The author is much indebted to Professor How chin, of 

 Adelaide University, for having in the first instance directed 

 his attention to this interesting problem and suggested its 

 investigation; and also to Professor David, of Sydney Univer- 

 sity, for kind discussion and criticism of the paper while in 

 manuscript form. 



By kind permission of the Government Geologist of South 

 Australia determinations of the alkalies in the greisenised 

 granophyres were made by Mr. W. S. Chapman, Analyst to 

 the Department of Mines, who also kindly made check deter- 

 minations of the alkalies of a number of other rocks. 



The author would specially mention his obligation to his 

 friend and colleague, Mr. C. E. Tilley, B.Sc, for assistance in 

 the field and in the laboratory, for many references to litera- 

 ture, and for much helpful discussion and criticism. 



The microphotographs were made by Mr. H. G. Gooch, 

 of the Geology Department of Sydney University, as were 

 also the excellent series of specially large rock slides on which 

 the petrological investigations were carried out. 



Geology Department, 



University of Sydney. 



