239 



to the eastern belt. Here the Thompson river has cut 

 completely through the outwash valley-train and has 

 deeply incised itself within the pre-Glacial floor of bed- 

 rock, forming a deep canyon. The canyon bottom con- 

 tains many huge blocks of rock that have tumbled from 

 above, and are now in process of being broken up and 

 carried downstream by the turbulent river. 



STRATIGRAPHY. 



The bed-rock geology has chiefly to do with formations 

 of Mesozoic and Tertiary age. 



The following is a table of formations in descending 

 order : — 



Approximate thickness (after 

 Dawson). 



Pleistocene and Recent. 



r 



Feet. 

 3,000 



Lower 1 

 Miocene (?) * ] 



I ,000 



Eocene (?) 



5,000 



Lower Cretaceous. 



5,000 



Jura-Cretaceous . . 5 , 000 



Superficial deposits. 

 Glacial till, gravel, sand, 

 clay and silt. 



Metres. 



914 Kamloops Volcanic group; 



basalt, agglomerate, breccia, 

 trachyte. 

 305 Tranquille beds; 



fine-grained tuffs. 



Cold water group; 

 1,524 conglomerate, sandstone, 



Ashcroft rhyolite porphyry. 



1,524 Queen Charlotte Islands forma- 

 tion (?); shales, conglomer- 

 ate and sandstone. 



1,524 Spence's Bridge Volcanic group; 

 andesitic and liparitic lavas, 

 tuffs, and arkoses. 



Upper Jurassic Granitic intrusives; batholiths, 



stocks, and tongues. 



Jurassic-Triassic. . 10,000 3,048 Nicola formation; greenstone, 



impure quartzite, argillite, 

 limestone, agglomerate and 

 tuff. 



Carboniferous. 



9,500 2,896 Cache Creek formation; cherty 

 quartzite, greenstone and 

 marble. 



* Dr. R. A. Daly refers these rocks tentatively to the Oligocene system. See page 149. 



