THE PURCELL RANGE AND THE ROCKY MOUNTAINS 131 



In the 180 miles which I studied, there are two distinct geo- 

 graphic provinces. In the northern province, which extends as 

 far south as Canal Flats, the trench is drained by the Columbia 

 River which has its source in Columbia Lake just north of the 

 Flats. The valley is narrow, for the most part not more than 

 3 or 4 miles wide. In part of this northern zone there is a wide 

 valley west of and parallel to the Columbia Valley, which joins 

 the trench at both ends and is only separated from it by a narrow 

 ridge, broken in one place. South of Canal Flats the valley is 

 drained by the Kootenay River, which comes into the trench from 

 the east and flows south. In this portion the trench becomes 

 much wider till it reaches its maximum width of 16 miles at Fort 

 Steele. South of there it contracts rapidly to 5 miles at Bull 

 River, but widens again at Elko and at Gateway. 



From what could be deciphered from the stratigraphy, it was 

 found that there are two principal series of rocks represented. 

 One is a great succession of Hmestones ranging from the upper 

 Cambrian to the Mississippian, but with rather large stratigraphic 

 disconformities. The other series is dominantly clastic, consisting 

 chiefly of various metamorphic phases of sandstone, shale, and 

 conglomerate. It has recently been determined, in at least some 

 cases, to be Cambrian, but probably includes much pre-Cambrian. 

 Probably its age overlaps somewhat that of the limestone series. 

 As shown on the map (Fig. i), this last series makes up most of 

 the west side of the trench in the northern zone, while the limestones 

 are on the east side and occasionally overlap to the west side. 

 South of Canal Flats the limestone series retreats into the Rocky 

 Mountains, and the clastic series crosses the trench, and occupies 

 a zone about 12 miles wide on the east side. Farther south, 

 between Bull River and Gateway, the limestone series again appears 

 in various hillocks in the trench and in narrow zones along its 

 sides. 



Structurally the trench has hitherto been considered as a sort 

 of Graben'' or at least the product of normal faulting.^ The results 



^ R. A. Daly, Geol. Surv. Can. Mem. 38, p. 600. 



" S. J. Schofield, "The Origin of the Rocky Mountain Trench," Trans. Roy. Soc. 

 Can., Sec. 4 (1920), pp. 73-81. 



