BY H. C. RICHARDS. 197 



and he has " indicated the grounds for regarding shales and 

 other sub-siliceous, hydrous sediments as more influential in 

 the generation of trachytic and syenitic magmas generally." 

 On these grounds of course the alkaline rocks in south-eastern 

 Queensland and in the Springsure area may be accounted 

 for, but it is difficult to explain why the outpourings from th& 

 same eruptive centre should be at one time calcic and at 

 another time alkalic when the same series of sediments- 

 are being intruded. A further matter to account for is 

 the reason for the middle series only of volcanic rocks being: 

 alkaline. 



All through the south-eastern Queensland area the 

 alkaline rocks are restricted to the middle series of the three- 

 fold development of volcanic effusions and the same holds 

 good in this area. 



Even if Daly's origin of the phonolitic material b& 

 accepted, it is difficult to account for the regular mode of 

 occurrence in south-eastern Queensland and at Springsure, 

 of the material in between the two developments of calcic 

 basic to sub-basic volcanic rocks. 



It is perhaps easier to reconcile such a regular occurrence^ 

 with a gravitative differentiation scheme as postulated by 

 Bo wen, or even with some modification of Marker's hypo- 

 thesis of crustal dislocation by radial movements. With 

 respect to Harker's hj^othesis the writer has not any 

 evidence at all as to crustal movements or otherwise in this^ 

 particular area. 



Age of Volcanic Rocks. 



With respect to the age of the volcanic rocks there is 

 no stratigraphical evidence except that they are later than 

 the Upper Bowen Series (Per mo -Carboniferous). On litho- 

 logical and chemical grounds, however, there seems to be no 

 reason for regarding them other than part of the Caino- 

 zoic development of volcanic effusions so abundantly 

 developed in eastern Australia. 



A close parallel can be drawn with the volcanic rocks 

 in south-eastern Queensland in sequence, on physiographic 

 grounds, and in lithological, mineralogical and chemical 



