CLA SSIFICA TION OF IGNEO US RO CKS 587 



Subclasses in Classes I, II and III are made on a fivefold 

 basis by considering the relative proportions of the two parts of 

 the salic group, just described. The reasons for using the salic 

 minerals in Class III, instead of the femic, are given in the dis- 

 cussion of Orders. In Classes IV and V Subclasses are formed 

 on the proportions of the two parts of the femic group. 



In Classes I, II and III the divisions will be as follows : 



In the first three'classes the distinctions between corundum 

 and zircon may be made in those subclasses in which they are 

 present in notable'amount, by the formation of Sections as follows : 



