[schofield] rocky MOUNTAIN TRENCH 89 



northwest from near the mouth of the Big Salmon River; this is, 

 doubtless, the continuation of one of the walls of the trough beyond 

 the wide break through which the Fraser escaped from it. The con- 

 tinuation of the trough in that direction is described by Mr. R. G. 

 McConnell.^ 



The Fraser pursues a most tortuous course in the strip of flat 

 land in the centre of the trough, swinging from side to side in broad, 

 sweeping curves, and sometimes approaching within short distances 

 of the enclosing ranges. In many cases very narrow necks are all that 

 remain to separate a higher from a lower bend, and numerous "ox-bow" 

 lakes along the course of the river bear witness to the frequency with 

 which similar necks have been cut through in the past. The tortuous 

 course of the river is due to the excessive load of sediment which it 

 carries, and not to a low gradient. The sediments consist largely of 

 flakes of mica and rock flour produced by the grinding of large glaciers 

 on the micaceous schists and gneisses, of which the mountains are 

 chiefly composed. Glaciers are comparatively rare on the side walls 

 of the trough, but are common in the higher ranges on either side of 

 them. The Fraser is not particularly turbid at Tête Jaune Cache, 

 but several of its tributaries, especially Sand Creek and Rau Shuswap 

 River, are heavily loaded with silts. The latter is the largest tributary 

 the Fraser receives m this part of its course, and drains a high, moun- 

 tainous country, in which many large glaciers were seen. On the other 

 hand, many of the smaller tributaries are clear, except after heavy 

 rains. Many of them do not head in glaciers, or else have lakes on 

 their courses which act as catchment basins for sediment derived from 

 glaciers. 



As has been stated, the country through which the Fraser flows 

 from the Grand Canon to Fort George belongs to a second topographic 

 type known as the Interior Plateau, and differs from the first in the 

 absence of regular mountain ranges. It is characterized by extensive 

 upland areas intersected by an irregular system of comparatively 

 broad valleys. Numerous lakes occur both in the uplands and in the 

 upper reaches of the valleys, and the streams are clear and become 

 quite warm in summer. 



9. The Fraser, Kickinghorse, and Elk Rivers which enter the 

 trench from the Rocky Mountains to the east have very steep grad- 

 ients. This is in marked contrast to the gradients of the Athabaska, 

 Bow, and Oldman Rivers which flow eastwards from the Rocky 

 Mountains to the Great Plains. This feature has been observed by all 

 the early explorers who entered the Rocky Mountain trench. 



1 Geol. Surv., Can., Ann. Rept., vol. VII, 1894, pp. 18-19C. 



