94 THE ROYAL SOCIETY OF CANADA 



2. Upper Columbia Lake, the source of the Columbia River, 

 stands several feet higher than the south-flowing Kootenay River and 

 is only prevented from draining into the Kootenay by a deposit of 

 gravel and sand. ' Some years ago a canal was constructed joining 

 this lake with the Kootenay River. 



3. "The Columbia River above the Surprise Rapids, which here 

 receives a stream of considerable size from the east, forms a narrow 

 lake-like expansion. In this part of its course there is only a com- 

 paratively low wooded ridge separating the Columbia from a wider 

 valley to the northeast, which is occupied by a tributary flowing in 

 the opposite direction and joining the Columbia just below Donald. 

 This is perhaps another hint that the Upper Columbia once flowed 

 southeast, before it had dug its way through the walls of slate above 

 Beaver." ^ 



4. As remarked by Dawson,^ the Rocky Mountain trench, at 

 least south of the Big Bend of the Columbia, in a general way is widest 

 in its southern portion. He also recognized for the first time that the 

 Columbia River in the Rocky Mountain trehch had originally a 

 southern outflow and also that the present condition of the valley in 

 regard to its drainage is both peculiar and anomalous. 



The south-flowing river which occupied the trench may be called 

 the proto-Kootenay. It embraced the drainage of the Nechako 

 which forms part of the headwaters of the Fraser above Fort George 

 and all the drainage southeast of this point along the Rocky Mountain 

 trench at least to Jennings Mountain. The present elevations of the 

 watersheds in the trench are as follows: — Fraser-Columbia, 2,600 

 (approximate), and the Columbia- Kootenay at Upper Columbia Lake, 

 2,650. These divides are at present covered with drift so that the actual 

 elevations of the bed-rock at these points is impossible of determin- 

 ation, but it may be assumed with some degree of certainty that the 

 elevations of the floor of the proto-Kootenay just previous to the 

 time of river capture by the Fraser and the Columbia Rivers stood in 

 the neighbourhood of 2,500-2,600 feet above sea-level since it is 

 scarcely possible that there has been any erosion at these points since 

 the date of river capture in the late Tertiary. 



The diversion of the drainage into the trench caused small 

 streams to flow towards the trench from the "through valleys" men- 

 tioned above and by headward erosion during the later Tertiary 

 times pushed the watersheds eastward along these valleys. Thus the 



1 Coleman, A. P., Trans. Roy. See, Can., vol. VII, 1889, p. 99. 



2 Dawson, G. M., Geol. Surv., Can., Ann. Rept., vol. I, 1885, p. 290. 

 Dawson, G. M., Trans. Roy. Soc, Can., vol. 8, 1889, sec. IV, p. 12. 



