On the Norian or "Upper Lcturentian" Formation. 301 



from place to place, the brecciated variety with a white 

 granular ground mass in which are enclosed irregularly 

 shaped fragments of dark blue plagioclase with some 

 streaks of pyroxene, but without distinct banding, and more 

 rarely, the streaked and distinctly banded varieties. All 

 these occur and pass into one another. The perfectly banded 

 and schistose varieties occur, indeed, only exceptionally, 

 yet one can observe indications of banded structure in 

 most places if large exposures are examined. The more 

 granular varieties occur principally on the east side, 

 exactly as in the Morin area. On Lake Kenogami, at the 

 south-east corner of the area, cliffs of the granular white 

 anorthosite occur which attain a height of 400 feet or 

 more, and which, through the entire absence of pyroxene 

 and iron ore, appear like great cliffs of marble.. 



It must here be observed that during the process of 

 granulation by which the large plagioclase individuals 

 were crushed into the granular ground mass, no alteration 

 took place in the chemical composition of the mineral. 

 The material acquired a much lighter colour through the 

 loss of the inclusions, but the composition of the feldspar 

 was not changed. This is evident from the fact that the 

 difference in the specific gravity of the two feldspars, 

 which was determined in the anorthosite of Mount 

 Williams, on the Shipshaw River, near the eastern limit of 

 the area, amounted only to 0.015. The large dark-coloured 

 fragments of crystals were naturally a little heavier on 

 account of the numerous dark inclusions which they con- 

 tain. Both feldspars were labradorites. 



The same fact was established still more clearly by 

 analyses made by Sterry Hunt of both crystals and the 

 ground mass of another anorthosite from the Chateau 

 Ricner area. These will be given in the table at the' con- 

 clusion of this paper, under Nos. I., II. and III. It will 

 be observed that the composition and the specific gravity 

 of the two are identical. Leeds showed the same to be 



