109 



relief by depositing a mantle of drift over the surface of 

 the region while in the main valleys the effect of valley 

 glaciation is evident in deepening and in transforming what 

 must have been a V-shape into a well marked U-shape. 



Valley glaciation has probably been, in part at least, the 

 cause of the formation of the hanging valleys, which are 

 so marked a feature of the Hedley district. Unequal 

 deepening of the main and tributary valleys by streams 

 revived by uplift may, however, also have been partly 

 responsible for the hanging valleys. 



The location of the valleys of the smaller streams 

 along their present courses has been dependent, in many 

 cases, upon the structure of the underlying rocks, and they 

 are consequently subsequent streams. It is not so clear 

 what were the causes determining the course and direction 

 of Similkameen river. It is inferred, however, from the 

 way in which that stream cuts across the axis of the Oka- 

 nagan range, that it must have occupied its present bed 

 prior to the Pliocene uplift, and consequently in relation to 

 the Okanagan range, it is an antecedent stream. 



Geology. The oldest rocks of the Hedley district are of 

 Carboniferous age and consist of massive limestones, thin 

 bedded quartzites and argillites, and a great thickness of 

 volcanic tuffs. They have been folded by pressure exerted 

 in an east and west direction, and in consequence dip 

 towards the west at angles varying from 15 to 90 degrees. 

 They are traversed by two sets of faults which strike 

 roughly northeast and northwest. 



Plutonic igneous rocks have been intruded through the 

 sedimentary rocks in the following order: — (i) diorite and 

 gabbro, (2) granodiorite. These igneous rocks have been 

 accompanied by a great number of apophyses, and followed 

 by lamprophyres, and other dyke rocks. 



Over all is a thin mantle of glacial and post-glacial 

 deposits. 



The following is a table of formations: — 



Quaternary — Stream deposits and glacial drift. 



Tertiary ? — Granodiorite. 



Mesozoic? — Diorite and gabbro. 



Carboniferous? — Limestone, quartzite, argillite, and 

 volcanic materials. 



The ore deposits of the district are of contact metamor- 

 phic origin and of a type unique among North American 

 deposits. They contain gold, the only valuable con- 



