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lines in the bed-rock formation. The canyon of Fraser 

 river is therefore a subsequent valley and is developed as a 

 result of rock structure. The composition of the rocks, 

 however, has had a marked determining effect on the shape 

 of the valley, for it is wide in the soft sedimentary rocks 

 and sheared granitic rocks but is narrow in the massive 

 igneous rocks. 



Fraser river, looking down from Yale; valley here widened out on greatly sheared 

 granite of the Coast Range batholith. 



If the course of Fraser canyon was defined in Eocene 

 times it is very likely that it has followed the same channel 

 down to the present, for the Eocene beds of the delta show 

 that there was no great structural disturbance, even in 

 Miocene times, in that part of the valley, such as might 

 cause the stream to shift its course. The absence of 

 Miocene and Pliocene delta deposits does not necessarily 

 disprove the idea that the stream persisted along that 

 course throughout those periods, because deposits of those 

 ages were probably carried farther out to a point now 

 covered by the sea before they came to rest, or if deposited 

 sooner have since been eroded away. It is more than 

 likely, therefore, that, having denned its course in Eocene 

 times, the Fraser has persisted along that course down to 

 the present. 



Long-continued erosion, acting throughout the early 

 and middle Tertiary, must have produced, by the beginning 

 35069— I IA 



