﻿190 Canadia7i Record of Science. 



against their igneous origin, for they have been regarded 

 as contact deposits, and have been referred by the writers 

 •cited above by Mr. Browne, to aqueous solutions. 



But as our knowledge increases of the changes that 

 take place in those molten magmas that have remained in 

 this condition some time before crystallizing, we have 

 come to recognize that very important differentiations 

 take place, and always with the relative increase of the 

 basic minerals toward the outer portions. Alfred Harker 

 has shown this for gabbros in England ; Pirsson has done 

 the same for syenitic rocks in Central Montana, and G. P. 

 Merrill for others in the south-western portion of the 

 same State. Many other observers have noted equally 

 significant, though less extensive manifestations of similar 

 phenomena. Instead of magmas being fairly homogeneous 

 and stable, we must regard them as quite the reverse, and 

 as subject to changes and differentiation, whose causes we 

 perhaps do not yet fully understand. 



It is not every magma that holds enough metallic 

 elements to yield an ore-body ; but where such are present 

 with sulphur, it is reasonable to infer that the resulting 

 sulphides would follow the course of the basic minerals. 

 If the latter tend to segregate toward the contacts, 

 so would the former. This is the line of argument that 

 has been previously followed. Mr. Browne's paper now 

 adds the further important point that even in small 

 amounts of fused matter, and above all in those made still 

 more fluid in the Orford process by the addition of sodium 

 sulphide, the two metals, nickel and copper, tend to 

 separate according to the relations that are observed on a 

 laro-e scale in ore-bodies. 



While we do not fail to appreciate that it is a long step 

 from a pot of fused matte to a great ore-body some 

 hundreds of feet in extent, yet the parellelism is very 

 significant, and it is fair to infer that what holds good for 

 the small amount would be even more marked in the large. 



