﻿Anorthosites of the Rainy Lake llegion. 233 



that the later feldspar is more acid than the older. In 

 one case a bytownite crystal has been broken, the parts 

 slightly shifted, and then cemented with labradorite, most 

 of the twin lamelhe running across the strip of cement. 



An analysis of a specimen from the mouth of Seine 

 River was made by Mr. William Lawson in the laboratory 

 of the School of Practical Science, Toronto, the results 

 l)eing given in column No. I. In No. II an analysis of 

 anorthosite from Rawdon, Que., made by Sterry Hunt and 

 (quoted by Dr. Adams, is given for comparison.^ No. Ill 



1 Uebei- (las Norian, p, 494. 



gives the results of an analysis of granite adjoining the 

 Bad Vermilion anorthosite area, and is the work of Mr. 

 Lawson. 



I. II. III. 



SiOo 46.24 54.45 76.20 



AI263 29.85 28.05 14.41 



Fe.203 1.30 0.45 



FeO 2.12 1.49 



MnO trace ... 



CaO 16.24 9.68 2.19 



MgO 2.41 ... 0.65 



Na^O 1.98 6.25 3.32 



K2O.. 0.18 1.06 2.44 



Co., 1.03 (H2O) 0.55 



101.35 100.49 100.70 



Sp. Gr 2.85 2.69 2.65 



The low percentage of silica and soda, and the high 

 percentage of lime, as compared with the anorthosite from 

 Quebec, are notable, and correspond to the results of 

 microscopic examination, the specimen from Seine River 

 consisting chiefly of anorthite, and that from Rawdon of 

 labradorite. The specific gravity, 2.85, is very high, per- 

 haps because of the presence of considerable zoisite. The 

 specific gravity of a specimen from Bad Vermilion Lake 

 was determined to be 2.76, corresponding to its slightly 

 more acid character, since it consists of bytownite. 



