62 THE ROYAL SOCIETY OF CANADA 



5. At the close of the Cretaceous, the two highlands and the 

 Interior Plateaus were uplifted, and the Rocky Mountains were slowly- 

 formed along the eastern border of the old land mass. The large rivers 

 which flowed to the east from the old eastern land mass were able to 

 keep their courses across the uprising mountain chain, forming the 

 through valleys of the Peace, Yellowhead, Bow, and Crowsnest 

 Rivers. Thus, the course of the Peace River, which drains eastward 

 from the old land mass across the Rocky Mountains, is normal, while 

 those of the Yellowhead, Bow, and Crowsnest Rivers are abnormal. 

 It is probable that at this time, subsequent streams, tributary to the 

 above-mentioned rivers, occupied the site of the present Rocky Moun- 

 tain trench; and that, therefore, the first faint beginnings of the trench 

 were made at the close of the Cretaceous or in very early Tertiary 

 times. 



6. Faulting along the line of the trench from the big bend of the 

 Fraser, at least to the 49th parallel, in early Eocene times, discon- 

 nected the through drainage, and diverted it into the Rocky Mountain 

 trench. The drainage at that time was southwards along the trench 

 and this primeval river, which for our purpose may be called the 

 proto-Kootenay, at this time included the headwaters of the present 

 Fraser and occupied the whole of the trench to the south. 



7. The Eocene Columbia River, which did not extend north- 

 wards as far as the Big Bend of the present Columbia River, and 

 hence had no connection with the drainage of the Rocky Mountain 

 trench, flowed southwards in a valley whose course, if projected 

 northwards, would intersect that of the Rocky Mountain trench, 

 whose trend is northwest-southeast. The Eocene Columbia River, 

 which had a much lower elevation than the river proto-Kootenay, 

 occupying the Rocky Mountain trench, eroded headwards during the 

 post Eocene times and captured a portion of the proto-Kootenay, 

 diverting part of it into the Columbia, and thus forming the peculiar 

 feature in the Columbia River known as the "Big Bend." 



8. The Fraser River flowing over the softer rocks of the Interior 

 Plateaus eroded headwards and captured the headwaters of proto- 

 Kootenay River, forming the "Big Bend" of the present Fraser. 



9. Subsequent erosion headwards of the Fraser and Columbia 

 during late Tertiary times gradually shifted the divides in the Rocky 

 Mountain trench to their present position and formed the rapid 

 portions in those rivers. 



10. Glaciation subsequently smoothed and removed the inter- 

 locking spurs, giving to the trench its modern trough-like character- 

 istics. 



