A TYPE OF LAKE FORMATION IN CANADA 25 I 



Pass, the altitude is still higher, and reaches 8500 feet above sea 

 level. On the other side of the pass in the valley of the Little 

 Fork of the North Saskatchewan, the evidence is almost identi- 

 cal, but with a downward slope of the ice line as the valley- 

 descends to the northwest. 



The highest erratic was found on a point near Mt. Assini- 

 boine, about twenty-five miles south of Banff, on the summit 

 of a mountain of limestone formation 8650 feet above sea level. 

 In the course of very many mountain ascents no transported 

 bowlders were ever observed at a greater height than this, nor 

 on isolated summits over 9000 feet above sea level were there 

 any evidences of general glacial action. 



The indications of former large ice streams which occupied 

 all these mountain valleys are found not only in the Bow Valley 

 but in the tributary valleys of the Saskatchewan and Athabasca 

 on the eastern side of the summit range, and of the Columbia 

 on the western side. In fact no mountain valley was observed 

 in which the same evidence was not more or less apparent, and 

 the line between glaciated and unglaciated surfaces rarely or 

 never appeared at an altitude lower than 7000 feet nor higher 

 than 9000 feet. This ice line is invariably higher in regions of 

 great elevation, near high mountain masses, in elevated valleys 

 and on mountain passes. It is evident then, from the arrange- 

 ment of drumlins, crag and tail formations, glacial grooves and 

 striations, and the transportation of erratics, that the present 

 drainage system was that of the ice currents, even at the time 

 of their maximum development. 



To this there are some interesting exceptions, a^ for instance, 

 in the Columbia Valley, where it appears that the ice formerly 

 moved southwards and the river now flows northwards. To find 

 a satisfactory explanation is not difficult. This valley is excep- 

 tional among the mountain rivers in having very little gradient 

 so that the river is sluggish and the valley is more or less 

 swampy. In other words, it would require only a slight eleva- 

 tion of the region to the north or a depression to the south to 

 reverse the direction of this stream. It is not necessary, how- 



