48 THE ROYAL SOCIETY OF CANADA 



on the west by the Coast range. This is the mountain portion and 

 constitutes the Fraser canon and is that which forms the subject of 

 this paper. 



From Agassiz to the sea coast, a distance of 70 miles, is the delta 

 portion. Here the mountains are some distance back from the river 

 course and the stream flows at a greatly reduced rate through a com- 

 paratively level plain of its own construction. 



The contrast between the mountain portion and the delta portion 

 is most marked, for the former exhibits features that have been pro- 

 duced entirely by the destructive forces of erosion while the latter is 

 mainly the result of the constructive forces of deposition. 



In that portion of the Fraser valley defined above as canon, 

 namely that from Lytton to Agassiz, the stream leaves the plateau 

 region through which it has flowed for hundreds of miles and becomes 

 confined between steep bordering mountains. The change from 

 plateau to mountain topography is by no means abrupt and is not very 

 noticeable from any point within the valley itself because of the depth 

 to which the valley is cut both in the plateau as well as in the mountain 

 portion. The change, however, becomes very evident as the stream 

 reaches the axial line of the Coast-Cascade mountain system between 

 North Bend and Yale, in that portion which forms the gorge. 



In this mountain portion the Fraser river acts as the dividing 

 line between the Coast and Cascade mountain systems and although 

 these mountain systems are so separated they nevertheless are very 

 similar in structure and are believed to belong to the same period of 

 uplift. 



The main characteristics of the mountain portion of the Fraser 

 valley, distinguishing it from other parts, are expressed in its grade, 

 depth, and shape. The grade ranges from 4 to 8 feet to the mile 

 reaching its maximum in the gorge itself. The depth of the valley is 

 one of its most marked features, being bordered by slopes which rise 

 quickly to heights of 2,000 feet or more and farther back to summits 

 which reach 7,000 feet in elevation. The shape of the valley is 

 U-shaped to flaring and is either terraced in gravel or other unconsoli- 

 dated material or shows benches of solid rock where it has been 

 deepened by the action of the stream. The slopes of the valley are 

 always well wooded, often to the summits of the hills behind and the 

 hills themselves, except in the case of the very highest, are rounded 

 and show the effect of somewhat mature erosion. 



The mountain portion of the Fraser valley is not uniform in 

 character throughout and can be divided in three distinct sections 

 depending on the physiographic characters of each. The upper 



