346 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



thoroughly crushed and altered that its exact original nature cannot be dis- 

 covered from an examination either of the ledges studied in the field or of the 

 five specimens collected to represent the stock. The microscope shows that the 

 rock was probably a common, medium-grained biotite granite. In its present 

 granulated and altered condition it offers little of petrographic novelty or 

 interest. 



The rock is coarse-grained and now gneissic. The original essential 

 minerals seem to have been orthoclase (now microcline), plagioclase (probably 

 oligoclase), and biotite. The abundant secondary minerals are red garnet, 

 muscovite, epidote, and kaolin. 



It is possible that this stock is a satellite of the gneissic batholith at and 

 west of Cascade. 



Trail Batholith. 



Definition. — There are but few regions of the world where post-Ai-chean 

 granites are exposed on such a grand scale as in the West Kootenay district of 

 British Columbia. Part of the district is included in the West Kootenay 

 reconnaissance sheet of the Canadian Geological Survey, a map covering about 

 6,500 square miles. More than two-thirds of this area is underlain by intru- 

 sive granites probably all of post-Carboniferous age. The whole group forms 

 a composite batholith, including variolas types and bodies called by Mr. Brock, 

 Nelson granite, Valhalla granite, Rossland alkali-granite, alkali-syenite, etc.* 



The delimitation of these different bodies has been accomplished in part, 

 but, from the nature of the surveys so far carried on, much work still remains 

 to be done before the composite batholith is fully mapped and its anatomy 

 understood. A leading difficulty in drawing boundary lines about the constitu- 

 ent intrusive bodies is found in the occurrence of many included masses of 

 crystalline schists and gneisses which may be in part of pre-Cambrian age 

 but to some extent are certainly metamorphosed post-Cambrian sediments or 

 else sheared phases of the intrusive granites themselves. Many large areas of 

 schistose rocks are thus not easy to classify. Among them is a group of 

 gneisses and schists occurring along the Columbia river from Sullivan creek 

 northward. They have been coloured as Ardhean on the West Kootenay sheet, 

 although McConnell, who carried on the reconnaissance of this part of the 

 district, states that these foliated rocks are largely ' contemporary in age with 

 the main granite area of the district' i.e. the Nelson granite.** The proba- 

 bility is, therefore, that the great granite body surrounding the town of Trail 

 is a direct offshoot of the vast batholith forming the central part of the West 

 Kootenay district and that, in the area bordering the Columbia between Robson 

 and Sullivan creek, it has been crushed to the gneissic condition. To that 

 portion of the composite batholith which forms a continuous mass with the 

 granite about Trail and belongs to the one date of intrusion, the name ' Trail 

 batholith ' may be given. 



* See West Kootenay sheet. 



** Marginal note on map of part of Trail Creek Mining Division, Geol. Surv. of 

 Canada, Preliminary edition, 1897. 



