268 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



quartz schist-mica schist series; this baiiding seems undoubtedly to represent 

 original bedding. The schistosity is for the most part apparently coincident 

 with it 



It looks as if the rocks of this belt lying to the west of the Rykert granite 

 form an appressed and greatly crumpled syncline but, in view of the scanty 

 field data, no great confidence can he felt in this interpretation. 



Petrography of Belt G. — The most easterly of the seven belts is even more 

 obscure as to its detailed structure than the other belts. Belt G lies between the 

 Bayonne and Bykert granite batholiths which have conspired to perfect the 

 metamorphism begun by the crush of earlier mountain-building pressures. 

 Half-way between the two batholiths and from four to five miles from either,. 

 the rocks have the peculiar habit of micaceous contact-hornfelses. Intense 

 crumpling of the sedimentaries in the zone has been brought ab'out by a combina- 

 tion of the strong orogenic pressure which has affected all the belts, and of the 

 outward pressures exerted during the forceful intrusion of the batholiths. The 

 structural problem of the belt is further rendered difficult by the rarity of good 

 bed-rock exposures. 



The belt is essentially composed of glittering coarse to medium-grained 

 mica schists. These vary in colour from light to dark greenish-gray and dark 

 rusty brown. The average phase is distinctly more ferruginous than the staple 

 schists of any of the other six belts. As a rule the schists are well banded, 

 much after the fashion of the spangled schists of belt E. 



It is believed that the bands represent the true bedding. The original 

 sediments were doubtless chiefly argillites more or less rich in silica, with 

 subordinate thin interbeds of sandstone. Their existing metamorphic equiva- 

 lents are muscovite-biotite schists carrying variable and often important 

 amounts of red garnet, yellow epidote, and tourmaline. The muscovite is some- 

 times sericite but generally occurs in the form of the usual foils of relatively 

 large size. 



As already noted, the northern part of the belt along Summit creek includes 

 schists which form the probable extension of belt E into the exomorphic collar 

 of the Bayonne batholith. All across belt G, at the creek, the strike is a little 

 north of east and thus roughly parallel to the contact-line of the batholiths 

 It is possible that similar peripheral schistosity was developed in belt G north 

 of the Rykert granite but this point could not be determined in the time that 

 could be allotted to the area. Elsewhere in belt G the average strike of the 

 banding varies from N. 25° E. to N. 45° E. The dips are exceedingly variable, 

 those observed ranging from 70° N.W., through vertieality, to 50° S.E. 



Thicknesses and Structure in the Priest River Terrane. — With the exception 

 of a few relatively unimportant bands of amphibolite, the whole of the. Priest 

 River terrane is composed of originally sedimentary rocks. The list of these 

 include argillites, argillaceous sandstones, highly silicious sandstones, dolomitic 

 sandstones and argillites, and dolomites. All these rocks are tremendously 

 sheared and metamorphosed, so that not a single ledge observed in the field 



