438 E. S. MOORE 



these elements, and the augite and olivine, separating out earlier, 

 caused some of the calcium and aluminium to be left over to enter 

 the dike. 



It is interesting to note that in the Sudbury and Cobalt areas, 

 where the Keweenawan rocks have suffered very great differen- 

 tiation compared with that in the Lake Nipigon region, there are 

 extensive ore bodies connected with them, while there is nothing 

 but a little iron ore in the Nipigon region, and this occurs at the 

 contact with sediments and may be leached from them. 



While differentiation of magmas and thus the separation of the 

 metals, as well as other elements, from the magmas, may be only 

 one factor in the development of mineral veins as well as mag- 

 matic segregations, it seems probable that all data collected on this 

 subject will show this is one of the important factors. Other 

 things being equal, if the igneous rocks are the source of the metals, 

 those magmas which show the greatest differentiation should be 

 the most favorable for the production of ores, whether they supply 

 metal-bearing solutions directly to the veins — a process quite 

 conceivable in some cases — or whether they cause segregation of 

 the metals so that they can readily be dissolved by meteoric waters 

 in sufficient quantities to form ore deposits in veins. 



