﻿506 THE NATURAL CLASSIFICATION OF IGNEOUS ROCKS. ["Aug. 191O. 



chemical analyses into the standard mineralogical composition 

 known as the norm : thus comparing the rocks mineralogically, 

 but yet without reference to their actual mineral composition and 

 physical structures, which after all were in a way accidental features 

 dependent not merely on the original composition of the magma, 

 but on its treatmeut during and after solidification. 



Dr. Teall thanked the Society on behalf of his friend the 

 Author for the way in which they had received the paper. There 

 appeared to be general agreement on the main subject of the paper, 

 for the criticisms had been almost entirely directed to the Quanti- 

 tative System of classification. Much of this criticism seemed to 

 him to be rather wide of the mark. Was the system of real utility 

 as aiding thought ? This, after all, was the important question, 

 and on the answer that would ultimately be given to it depended 

 the fate of the classification. 



