588 CROSS, IDDINGS, PIRSSON, WASHINGTON 



Section 3 

 Section 4 



Section 5 



In Classes IV and V, Sections may be made analogously, when 

 it is necessary to recognize distinctions between notable amounts 

 of apatite and various metals and sulphides. They need not be 

 given here as the principles controlling them are the same as 

 above. 



It will be noted that the vast majority of igneous rocks of all 

 Classes belong to the first Subclass in each Class. There are few 

 rocks known belonging to most of the Subclasses here proposed, 

 but if ever found their classification is thus provided for and 

 will not disturb that of the rocks already known. 



In the remainder of this article the classification set forth 

 pertains to Subclasses I of each of the five Classes, unless other- 

 wise stated. 



Orders. — The division of Subclasses to form Orders is made 

 on a basis of the relative proportions of the standard minerals in 

 the preponderant group. 



For Classes I and II the preponderant minerals are salic ; and 

 in Class III salic minerals are considered before femic, and since 

 minerals of Part I are preponderant over those of Part 2 the 

 former are made the basis of subdivision, which is as follows : 



a) Quartz, Q. 



b) Feldspars (orthoclase, albite, anorthite), F. 



c) Feldspathoids (lenads) (leucite, nephelite, sodalite and nosel- 

 ite), L. 



Owing to the fact, already discussed, that quartz and the 

 feldspathoids (lenads) are in almost all cases antithetical, so that 

 they do not occur together, these three factors may be employed 

 serially and in the first three Subclasses of Classes I, II and 



