CLASSIFICATION OF THE PLUTONIC ROCKS 251 



Plotting these results in the manner described, the following 

 figure is obtained : 



SiO 



Fig. 1. 



In the following pages the analyses of the best-known types in 

 each series are given, each table of analyses being illustrated by 

 a diagram on which the molecular proportions calculated from 

 the same analyses have been plotted according to the method 

 devised by Iddings. In selecting the analyses I have made 

 use of Brogger's useful averages, calculated from well-known 

 types of diorite, monzonite, potash-syenite (plauenite), and 

 soda-syenite. In each other case as typical an example has 



* The ferric oxide (Fe 2 O a ) can be plotted on the FeO line and beyond the FeO ; 

 but this is not essential to the present purpose. 



