[schofield] 



ROCKY MOUNTAIN TRENCH 



93 



The Eocene History 



The normal faulting which occurred in the Rocky Mountain 

 trench as stated in a previous chapter, took place probably in Eocene. 

 This faulting produced not only a depression along the line of the 

 trench from the neighbourhood of the Big Bend of the Fraser south- 

 wards to the International Boundary at the 49th parallel, but 

 also a zone of shearing which would also be a zone of weakness along 

 which rivers would tend to erode rapidly. The Fraser, Yellowhead, 

 Bow, and Crowsnest Rivers which crossed the trench previous to the 

 faulting would have their courses interrupted by the depression 

 caused by the faulting, and their waters turned into the trench. That 

 the drainage of the trench was evidently southwards is supported by 

 the following (Figure 4) : 



Modern drainage . 



Drainage after Late Eocene /au/ti/y- -_ — > 



Geo/o^/ca/ Sarvey. Canada. 



Figure 4 



1. The Spillimacheen River, a tributary of the Columbia, rises 

 about 12 miles south of the main line of the Canadian Pacific Railway 

 on the west side of the trench and flows southwards for 30 or 40 

 miles in a valley almost parallel to the Columbia River which flows 

 northwards. 



