﻿2.') 2 Canadian Record of Science. 



purplish color is no doubt the result of weathering, which 

 has generally progressed rather far, though cleavage sur- 

 faces showing twin striations can be found generally. The 

 freshest example studied comes from a hill at the mouth 

 of Seine Eiver. 



In the numerous thin sections examined more than 

 nine- tenths of the rock is seen to consist of plagioclase, 

 usually sprinkled with zoisite particles or more or less 

 completely changed to a saussuritic mass. The darker 

 portions lying here and there in angles between the feld- 

 spars consist mainly of a fibrous or scaly mineral with 

 parallel or nearly parallel extinction and low double 

 refraction, probably serpentine, but perhaps a member of 

 the chlorite group. Augite was found as a remnant only 

 once, and then was not of the diallage type. No other 

 primary minerals were observed, not e^^en magnetite ; and 

 very few secondary ones require to be added to those 

 mentioned, only epidote, probably some albite, and a very 

 little calcite. The feldspars, w^here fresh enough to study, 

 show broad twinning according to the albite and frequently 

 also the pericline law, the former ranging in angle of 

 extinction from the twin plane between 17° and 37". 

 The average extinction angle in thin sections from Bad 

 Vermilion Lake is about 24°, and from the mouth of Seine 

 Eiver 32^ The former feldspar is therefore bytownite 

 and the latter anorthite, both more basic than that of the 

 typical anorthosite, which Dr. Adams finds to be labra- 

 dorite. 



In the freshest section studied (783, mouth of Seine 

 Eiver) the large interlocking feldspar individuals often 

 show a thin band of fresh, clear feldspar where one joins 

 the other ; and this clear feldspar strip is seen, when exam- 

 ined with a high power, to form a secondary enlargement 

 of the adjoining crystals, the twin striations running out 

 into it. The extinction angles of these secondary feldspar 

 rims vary from 8° to 14°, corresponding to labradorite, so 



