352 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



feet wide, and the zone is impregnated with small qnartz veins. This fracturing 

 of the conglomerate may have been contemporaneous with the intrusion of the 

 porphyry. 



The conglomerate is not so coarse as that at Sophie mountain or Lake 

 mountain and carries more sandy layers. A. second difference was seen in the 

 occurrence of a higher proportion of pebbles derived from the adjacent volcanics. 

 Here, too, there are pebbles of an equigramilar biotite granite. Quartz, quart- 

 zite, slate, and chert are the other staple materials of the pebbles. 



Conglomerate Area at Monument 169. — Another five miles farther west, at 

 monument 169, the Boundary slash crosses a patch of coarse conglomerate, 

 covering about one-quarter of a square mile. This mass has been upturned, 

 with strike N. 80° W., and an average northerly dip of 75°. The well-rounded 

 pebbles, ranging from two inches or less to ten inches in diameter, are chiefly 

 composed of altered porphyritic latite (or andesite?), most probably derived 

 from the Bossland lavas in the immediate vicinity. Compared to them the 

 quartzitic and slaty pebbles are quite subordinate, but lenses of dark-gray, 

 quartzitic sandstone, like many such lenses in the eastern areas of conglomerate, 

 are occasionally intercalated. At this locality contemporaneous latite flows 

 seem to be interbedded with the conglomerate. 



Correlation and Origin.- — These conglomerate areas have all been mapped 

 under the same colour, though it may well be that they are of different ages. 

 Proceeding from east to west the pebbles of the different occurrences are com- 

 posed more and more often of material which in the field is indistinguishable 

 from the adjacent Rossland lavas. At the same time the pebbles become more 

 rounded. The local character of the four areas, their alignment and the 

 similarity in the composition of the quartzitic, phyllitic, and slaty pebbles to the 

 rocks forming the Summit series and Priest Paver terrane as well as the Pend 

 D'Oreille group of the Selkirks — these facts suggest the hypothesis that the con- 

 glomerate everywhere represents a heavy mass of river gravels, and that one or 

 more streams flowing westward from the site of the present axis of the Selkirk 

 range were responsible for the accumulations. The deposit of dicotyledonous 

 leaves in the coarse Sophie mountain conglomerate strongly indicates the fresh- 

 water origin of that mass at least. It is clear, however, that we have nothing 

 clear or decisive regarding the correlation of the conglomerate bodies with one 

 another or with the recognized systems of rocks. The high probability is that 

 they are all pre-Miocene and post-Jurassic. 



Beaver Mountain Group. 



General Description. — In 189S Mr. E. W. Brock made a brief reconnaissance 

 of the mountains situated between Beaver creek, and Salmon river and south 

 of the Nelson and Fort Sheppard railway. As a result of his work he has 

 mapped a portion of the volcanic rocks of the district as belonging to a special 

 division, the ' Beaver Mountain Volcanic Group.' A very brief description of 

 the group appears in the marginal Explanatory Notes on the West Eootenay 



