316 J. A. THOMSON. 



developed there, viz. the occurrence of albite granites and 

 the presence of albitisation amongst the older (amphiboli- 

 tised) quartz-dolerites. If, on the other hand, the commonly 

 occuring rock types are correctly accounted for as anchi- 

 eutectic rock, as many authors are now willing to believe, 

 there would be a tendency for the development of similar 

 rocks from widely different primary magmas. That such 

 'diphiletic' 1 rocks are present in the case of the Atlantic 

 and Pacific suites has been consistently denied by Rosen- 

 busch, but even he is unable to ascribe most basalts to one 

 or the other suite, and other observers believe in the 

 possibility of diphiletic rocks. It would not do to push this 

 possibility too far in connection with the views suggested 

 above, or the primary chemical peculiarity postulated above 

 would not be deducible from such a diphiletic anchieutectic 

 rock. 



Summary and Conclusions. 

 A series of seventeen rocks collected by the Elder Scien- 

 tific Exploring Expedition from the neighbourhood of the 

 eastern boundary of Western Australia are described in 

 detail, and compared with the rocks of the Western Aus- 

 tralian golclfields. Only one resembles the immediate 

 country of the auriferous veins. Two are probably to be 

 referred to the gneiss formation. The remainder are dyke 

 rocks; they include a camptonite, the first undoubted 

 occurrence of this type in Western Australia, and a num- 

 ber of very fresh intrusive dolerites of considerable peno- 

 logical interest, especially in that they are the first rocks 

 on the Australian mainland in which enstatite-augite and 

 pyroxene-perthite have been recorded. A comparison of 

 these rocks with the later dykes of Western Australia and 

 the dolerite sills of Tasmania, Antarctic and South Africa 



1 I am not aware whether the term diphiletic has been used before in 

 this sense. It was suggested to me in conversation by Dr. J. S. Flett. 



