354 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



thicker masses of agglomerates are inter-bedded with the shales and sandstones. 

 The relations are similar to those of the Mesozoic shales and sandstones which 

 dip under the Sophie mountain-Malde mountain breccia at Little Sheep creek. 

 The characters of sediments, lavas, and pyroclastics are also suggestively like 

 those of the formations at that fossiliferous locality. The agglomerates inter- 

 bedded with sandstones and shale in the more southern of the two sedimentary 

 areas, i.e, at the south end of the long Beaver Mountain ridge, carry a few 

 small fragments of white marble which is like that in the Sophie mountain 

 agglomerate. There is thus some ground for referring the Beaver mountain 

 sediments and volcanics to the Mesozoic. 



In none of the traverses made, either by Mr. Brock or by the writer, has 

 it proved possible to construct a trustworthy columnar section of these rocks. 

 The group is greatly disordered by faulting and by the intrusion of dikes and 

 sills. The greatest difficulty was, however, due to the lack of sufficiently con- 

 tinuous exposures. It is known only that the clastic rocks are of the notable 

 thickness of over 1,000 feet and that they conformably underlie a great thick- 

 ness of lava and associated pyroclastic material. All these rocks have been 

 upturned and dip at all angles up to that of 90°. The strike is highly variable. 



Volcanics. — So far as known, the lavas of the group belong only to the two 

 related species, augite andesite or olivine-free basalt, and in largest part to the 

 former species. The agglomerates and ash-beds, which are exposed on a great 

 scale, are chiefly accumulations of the same basic lavas in pyroclastic condition, 

 but along with those fragments there occur variable amounts of black shale, 

 slate, and gray sandstone, with a little vitreous quartzite and white marble. 

 Petrographically, the andesite and basalt are indistinguishable from the same 

 types where these were observed in the area mapped as underlain by the 

 Rossland volcanic group. Notwithstanding the profound disturbance which the 

 Beaver Mountain rocks have suffered, they are seldom or never schistose over 

 any considerable area. The metasomatic changes are rarely so great as to 

 obscure the true nature of the lavas, though the extreme freshness of the 

 Miocene lavas west of Midway was not observed in any thin section cut from 

 these rocks. 



Sheppard Granite. 



One of the youngest intrusives of the Selkirk and Columbia ranges is alka- 

 line biotite granite, which forms a small stock at the head of Sheppard creek, 

 there cutting the older traps of the Rossland volcanic group. This acid type 

 may, for convenient reference, be named the Sheppard granite. ' The same 

 granite composes a larger stock south of Lake mountain, a small lenticular mass 

 near the summit of that mountain; also a stock and some large, dike-like masses 

 on the lower Pend D'Oreille river, as shown on the maps. In all the bodies 

 the granite is generally quite uniform in character and the following descrip- 

 tion of the rock, where outcropping at the head of Sheppard creek, will suffice 

 for all of the occurrences. 



