2 3 8 



and sands, were laid down under water and are intercalated 

 in the White Silt formation. 



Following the complete withdrawal of the ice from this 

 portion of the Cordillera, the denuded region of former 

 vigorous glaciation would supply but little rock waste 

 to the streams. With the reduction in waste supply and 

 but a moderate reduction in volume, the streams here 

 deeply degraded the earlier accumulations. Degrada- 

 tion was probably further aided by regional uplift which 

 invigorated the streams. Terraces due to the normal 

 lateral swinging of the river, as well as to later minor 

 stages of alluviation and degradation dependent upon 

 climatic change, are present throughout the Thompson 

 valley. An old river bed is found to lie persistently in 

 sharp contact with the White Silt for many miles. It 

 is represented by a coarse gravel with boulders over- 

 lapping each other in the direction of flow. It is generally 

 found directly beneath the surface silt and sand of the 

 terrace on the bed-rock side of the valley. 



The district between the east end of Kamloops lake 

 and Lytton may be divided into three distinct sections. 

 The eastern section covers Kamloops lake, where the 

 Thompson valley appears to have been glacially deepened 

 to a great extent The result is that the tributary valleys 

 bear hanging relationships to the main valley. There 

 are well developed alluvial fans and cones chiefly of sub- 

 aqueous origin, at the mouths of the tributary creeks. 

 The main valley itself is comparatively free from glacial 

 outwash material. 



The central section extends from the west end of Kam- 

 loops lake (26 miles — 42 km.) to Thompson Siding (85-3 

 miles — 158km.). It is characterized by a great depth of 

 Glacial valley-train material, beautifully terraced by the 

 meandering Thompson river. The deeply incised river, 

 however, has only in a few places reached the rock floor 

 of the old pre-Glacial valley. 



The western portion of the central section from Toketic 

 to Thompson Siding, owing both to the increased gradient 

 of the river and the narrowness of the valley, contains 

 only narrow terrace lands, and a comparatively small 

 development of the White Silt formation. 



The western section, from Thompson Siding to Lytton 

 (9-48 miles — 153 km.) — the Thompson Canyon proper — , 

 displays a very mountainous appearance in bold contrast 



