58 THE ROYAL SOCIETY OF CANADA 



more fully under the Ste. Monique occurrence, where its develop- 

 ment can be traced in more detail than in the other areas. 



The rock, therefore, has crystallized in two generations, as follows : 



Some resorption apparently and a 



Magnetite second crystallization as follows: 



Perovskite • Chrysolite 



Apatite Biotite 



Chrysolite Monticellite 



Augite Magnetite 



Biotite Melilite 



Thus the rock is a monchiquite which has altered during the 

 process of cooling to a monticellite alnoite. The way in which these 

 later minerals were formed and the nature of the magma from which 

 they were derived has been fully discussed in Bowen's paper on the 

 Isle Cadieux occurrence, with the exception of the calcite. 

 1^ The Fine-Grained Variety.— The fine-grained variety consists of 

 the same minerals as the principal type although there are some 

 minor variations in their associations and manner of occurrence. 

 The mode of alteration and resorption of the augite and chrysolite 

 can be more clearly ascertained as the rock is fresher than that 

 comprising the principal type. 



One large augite grain (1.5 by 3 mm.) with rounded outline was 

 observed. This grain is slightly brownish in colour, with a pleochroism 

 so slight that it could not be determined. The mineral displays a 

 perfect cleavage along which no alteration has taken place. Cracks 

 are lacking, but iron ore and perovskite grains about 0.01 mm. in 

 diameter are arranged along lines or forming sprays with no apparent 

 regularity as to direction. Around the border there is a practically 

 continuous rim of magnetite and perovskite, and outside of this border 

 is an arrangement of biotite and melilite laths forming a wreath about 

 the large crystal. 



Other individuals have been altered along cleavage cracks to 

 biotite. In these cases the rim of magnetite and perovskite is present, 

 but there are few inclusions in the interior of the grain. In the ma- 

 jority of cases, the augite is in small grains, in groups consisting of 

 several individuals in optical continuity, separated from one 

 another by laths of biotite and melilite exhibiting a tendency to flow 

 structure. In places, neighbouring grains are oriented at a small 

 angle to one another, showing the possibility of some slight movement 

 after the partial resorption of the original crystal of which these frag- 

 ments are undoubtedly the remains. The iron ore is frequently 



