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 bod}^ of rock, which the vast period of 

 post-Silurian denudation has not been sufficient to uncover. 



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

 the Nwth Hercules Section, Mount Read. 

 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. Per cent. 



Silica 75-73 



Alumina 12-70 



Oxide of iron 2-25 



Lime 2-00 



Magnesia 0*60 



Potash 2-04 



Soda 3-48 



Loss at red heat 1-20 



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. 



