ROCK SPECIMENS FROM CENTRAL AND WESTERN AUSTRALIA. 315 



Whether the similar recurrence of these rocks at different 

 periods of geological history will be found so abundantly 

 elsewhere as to invalidate the force of this argument, so 

 far as it applies to the rocks of Gondwana Land, remains 

 for the future to disclose. In so far as it applies to Aus- 

 tralia, it opens up a fruitful field of enquiry for Australian 

 petrologists. 



Note. — Since the above was written, an important paper 

 by Dewey and Plett has made suggestions that to some 

 degree undermine the above views. 1 In effect, they pro- 

 pose to recognise besides the well known Atlantic and 

 Pacific suites of rocks yet a third known as the spilitic, and 

 geographically associated with districts of long continued 

 and gentle subsidence. The rocks characterising the suite 

 are picrite, diabase (often albitised), minverite, quartz- 

 diabase, keratophyre, soda felsite and albite granite. The 

 most striking chemical peculiarities of the group are the 

 richness in soda compared to potash and lime, not indeed 

 always to be seen in the original minerals, but betrayed by 

 the juvenile albitisation that the rocks have undergone. 



Quartz-dolerites, then, are claimed by them as belonging, 

 at least in part to the spilites, both on account of the 

 albitisation which they sometimes exhibit and of their 

 geological relationships with other members of the suite, 

 whereas in the ideas put forward above, they are attached 

 to the charnockite suite on account of their relative rich- 

 ness in iron and magnesia. It must be admitted at once 

 that the above authors have a far stronger case for their 

 general view, based as it is on a much greater body of 

 observation. There are even features in Western Australia 

 that give support to the possibility of the spilite suite being 



1 Dewey, H, and Flett, J. S ., British Pillow-lavas and the Rocks 

 associated with them. Geol Mag„ Dec. 5, Vol. vm, 1911, pp. 202-9 and 

 241-8. 



