264 



of the Pliocene period, a fairly mature valley with wide, 

 flaring sides, and a floor several hundred feet above the 

 present stream bed. A well defined topographic break on 

 the slope of spurs projecting into the valley 1 ,500 (457 m.) to 

 2,000 feet (784 m.) above the present stream bed may 

 mark the old valley slope. When the Pliocene uplift took 

 place, elevating the Cascade range and the adjacent 

 part of the Coast range, the stream was revived and the 

 deepening of the gorge was begun. 



At the close of the Pliocene the canyon was problably 

 sharper than the present canyon with, however, the 

 same variations in character due to the relative resis- 

 tance of the rock formations Glaciation subsequently 

 widened the bottom of the valley to its present shape. 



At the close of the Glacial period the land was depressed 

 below its present level and unconsolidated deposits of sand 

 and gravel were laid down in the bottom of the valley to a 

 depth of several hundred feet. 



Elevation of the land in relation to the sea has since taken 

 place, and the erosive power of the stream has again been 

 revived. It has consequently cut down through the 

 Glacial deposits, leaving a series of terraces at different 

 levels to mark successive stages in the deepening of the 

 valley. In the gorge, deepening has progressed through 

 these Glacial deposits and into the solid rocks below to a 

 depth of about 100 feet (30-5 m), leaving remnants of the 

 old valley floor as rock benches on one side or the other of 

 the stream. The amount of uplift appears to have been 

 greater in the interior than on the coast. 



REFERENCES. 



Selwyn, A. R. C. — G.S. C, Rep. of Progress 1871-72, 

 Part II. Rep. of Progress 1877-78, 

 Part B. 



Dawson, G. M. — G.S.C., Rep. on Kamloops Map Sheet, 

 Vol. VII , Part B. 1894. 



Camsell, Charles — G.S.C., Summary Report, 191 1. 



Bowen, N. L. — G.S.C., Summary Report, 1912. 



