260 



located in granitic rocks, and broader and more open 

 where the bed rock is the more easily eroded sedimentary 

 rocks. In cross-section it is more or less U-shaped from the 

 effect of valley glaciation. 



In the wider portions of the main canyon gravels have 

 accumulated to a considerable depth, but in the more 

 constricted parts deposits of this nature are rare and of 

 very limited extent. The gravels were deposited in the 

 closing stages of the Glacial period, but as a result of later 

 deepening of the stream bed a large part of them has been 

 removed and the remainder left as terraces, marking 

 successive stages in that deepening. As many as a dozen 

 terraces can be counted in the valley at Lytton. Uplift 

 since Glacial times has given the stream such renewed 

 power of erosion as to cause it to cut dcwn not only through 

 the sands and gravels, but even to deepen its bed into the 

 solid rock, leaving rock benches here and there on one side 

 or other of the valley bottom. Benches of this nature 

 are noticeable at Spuzzum and near Saddle Rock. 



The grade of the stream varies from about 4 feet to the 

 mile (-76 m. per km.) in the portions above and belcw the 

 inner canyon to 8 feet to the mile (1-52 m. per km.) in 

 the inner canyon itself. 



Virtually all the streams tributary to the Fraser river 

 along the main canyon, and particularly those of small 

 volume, enter through hanging valleys. The develop- 

 ment of the hanging valleys is in the main due to glaciation 

 though in one or two instances the hanging valley effect is 

 heightened by post-Glacial deepening of the main stream 

 itself. 



GEOLOGY. 



Stratified rocks of Carboniferous age (Cache Creek) 

 consisting of cherty quartzites, argillites, limestones, 

 serpentine and volcanic flows are the oldest rocks in the 

 main canyon. These rocks have been greatly disturbed 

 and now dip at high angles, striking diagonally across 

 the river. They have been in part intruded by granitic 

 rocks and in part covered by later stratified rocks so that 

 they now have a small areal extent. 



Plutonic igneous rocks, mainly granodiorite, are exposed 

 throughout a great part of the main canyon, especially 

 in the gorge below North Bend. They belong to the great 



