BY H. C. RICHARDS. 199 



rocks from acid to basic, and occurring in all three divi- 

 sions; and (c) a series intermediate between (a) and (&), 

 containing rocks ranging from acid to basic and in all 

 three divisions. 



The chemical characters of the rocks in comparison 

 with alkaline and sub-alkaline rocks in general is shown 

 by means of variation diagrams. A general paucity in 

 alumina with a corresponding richness in total iron-oxides, 

 a slight lack of lime and magnesia, and a slight excess of 

 alkalies, especially soda, are characteristic of both series. 



It is considered improbable that the assimilation of 

 limestone material &c. by the primary magma took place 

 to form the partial magmas from which all the alkaline 

 rocks were formed in this area. 



An estimate of the chemical nature of the original 

 parent magma from which all the volcanic rocks have 

 been derived has been made, and compares very closely 

 with that of the average andesite as given by Daly. 



During the Cainozoic era, this area was a sub-alkaline 

 province, but during the middle portion of the era, several 

 small alkaline sub-provinces existed. 



The volcanic alkaline rocks constitute at the most 

 5 per cent, of the volcanic material. 



Harker's generalisation that sub-alkaline rocks are 

 associated with folding earth movements is not borne out 

 by the evidence from this area. 



The nature of the parent magma, its differentiation 

 with the resulting series of rocks, and the sequence of the 

 flows have been discussed. 



A geological sketch-map and four sketch-sections have 

 been prepared to show the distribution, extent and strati- 

 graphic relationships of the rocks of the area; also from 

 the chemical analyses a number of variation diagrams and 

 a set of Brogger diagrams have been drawn up to show 

 the relationships of the volcanic rocks to one another; a 

 series of microphotographs of the more important rocks is 

 also appended. 



