[camsell] great canon OF FRASER RIVER 51 



In the main the gorge portion of the valley is steeply U-shaped, 

 but the bottom of the U-shaped valley has been notched by stream 

 action to a depth of about 100 feet, with the result that there is now a 

 narrow V-shaped or almost box-shaped gorge cut into the bed of the 

 upper U-shaped canon. The result is, that instead of having gravel 

 benches on either side of it, the stream is generally flanked by a rock 

 bench about 100 feet high above the level of high water. The narrow- 

 ing of the main valley itself is enough to give a canon effect, but the 

 notching again of this valley has resulted in the formation of a canon 

 within a canon. 



Whatever may have been the cause of the location of the valley 

 along its present lines, the formation of the gorge appears to be due to 

 one or both of two causes. In the first place the gorge lies entirely 

 within granitic rocks and its narrowness appears to be due to the 

 superior qualities of resistance to erosion that such massive rocks 

 have over the softer sedimentary rocks, thus giving rise to the steep 

 slopes of the valley sides. On the other hand, the gorge lies directly 

 in the central line of uplift of the Coast and Cascade mountain systems 

 and its formation may be due to greater and more recent uplift along 

 that line while the stream was continuing to deepen its bed. From 

 evidence obtained in adjacent regions we know that these two moun- 

 tain systems were elevated in late Pliocene times S^ and their structure 

 shows that this elevation was not cataclastic in its nature, but was in 

 the nature of a slow regional uplift. There is evidence in the canon 

 itself that there has been an uplift since the valley had been occupied 

 by glacial ice, for there is exhibited in it an unglaciated inner canon 

 formed in the bottom of a glaciated upper canon, showing that the 

 inner canon has been incised since glacial times to a depth of at least 

 100 feet. That incision could only have been made by a stream 

 revived by uplift. 



The grade of the gorge in high water is reckoned at 8.4 feet to 

 the mile and the stream is consequently rapid. The volume of water 

 flowing through the gorge has not been measured, but even in a stage 

 of low water it must be very great, seeing that the river system drains 

 an area of over 91,000 square miles. 



Such a volume of water in a stream of 300 or 400 feet in width 

 makes a tide that the most powerful steamer would have great diffi- 

 culty in stemming, but when that width is reduced by half, as it so 

 often is in many of the constrictions which are found throughout the 



1 Dawson. G. M., Bull. Geol. Soc. Am., Vol. 12, p. 90. 1901. 



2 Smith, G. O., U.S. Geol. Surv., Prof, paper No. 19, 1903. 



