46 



ON FELSITES AND ASSOCIATED ROCKS. 



felsites. The long line of felsite, with its axial direction 

 parallel with that of the West Coast range, shows that below 

 that area, in Silurian times, there must have been a corre- 

 sponding plutonic body of rock, which the vast period of 

 post-Silurian denudation has not been sufficient to uncover. 



Mr. W. F, Ward's Analysis of Quartz-kerataphyre from 

 the North Hercules Section^ Mount Mead. 



Professor Rosenbusch suggested to us that a chemical 

 analysis of this rock was highly desirable, in order to 

 confirm the results of optical examination. This analysis 

 has been made by Mr. W. F. Ward, Government Analyst, 

 who states it as follows : — 



Constituents. 



Silica 



Alumina 



Oxide of iron 



Lime 



Magnesia 



Potash ., 



Soda , 



Loss at red he^t . 



Per cent. 



75 



12 



2 



2 





 2 



3 

 1 



•73 

 •70 

 •25 

 •00 

 •60 

 •04 

 •48 

 •20 



100 • 00 



From the above it will be seen that the reference to 

 quartz-keratophyre is fully sustained. The percentage of 

 silica shows it to be an acid eruptive, while the excess of 

 .soda over potash indicates the keratophyre group. 



