228 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



With the addition of one type, the list of rock varieties recognised in the early 

 publications will serve for all the bodies to be described. The description of 

 the individual sills may be anticipated by an account of all the phases, 



MOYIE MOUNTAIN 



Figure 14.— Section of Moyie mountain and the Moyie sills, along the International 

 Boundary line. Sills in solid black. Bedding-planes of the quartzite and fault- 

 planes shewn. 



beginning with the most acid one, a granite, and ending with the most basic 

 and ferromagnesian one, a metagabbro or abnormal hornblende gabbro. The 

 following account of petrography and theory will largely consist of a revised 

 edition of that contained in the 1905 and 1906 papers. 



ABNORMAL BIOTITE GRANITE. 



In sills A, C, and D the intrusive rock forms distinctly acid zones. The 

 chief constituent is a biotite granite. This is a gray rock, much lighter in tint 

 than the deep green gabbro (Plate 34). The grain varies from quite fine to 

 medium. Very often roundish grains of bluish, opalescent quartz interrupt the 

 continuity of the rock. These are considered to be of exotic origin as they were 

 seen to graduate in size into larger blocks of quartzite (xenoliths) shattered 

 from the sill-contacts. 



To show the average composition of the granite, and the approximate 

 limits of its lithological variation, fresh specimens, taken from sill C at three 

 points in the section following the wagon-road, west of the mountain, will be 

 described. They were collected at respectively 15, 40, and 50 feet from the 

 upper contact with the quartzite. 



The specimen taken at a point 15 feet from the contact, and representing 

 what may be called Phase 1, has the macroscopic appearance of a finely granular 

 gray granite. In thin section it is seen to be a micropegmatite with a hypidio- 

 morphic granular structure sporadically developed in many parts of the section. 

 The crystallization is confused and does not show the regular sequence of true 

 granites. The essential constituents are quartz, mieropegmatite, micro perthite, 

 ©rthoclase, oligoclase-andesine and biotite; the accessories include titaniferous 

 magnetite, a little titanite, and minute acicular crystals of apatite and rarer 

 zircons. The characters of all these minerals are tho?e normally belonging to 



