GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 7 



uplifted peneplain, similar to that observed by Gilbert farther north in Alaska. 1 

 The upheaval of such a mass, by lateral pressure, would give rise to troughs and 

 open gaping crevices parallel with the previously formed mountain folds and 

 into these the drainage streams would, for the most part, be diverted. Deepened 

 by stream action, widened by atmospheric agencies, and still further modified 

 by Pleistocene glaciers, we have the longitudinal valleys of the Rockies and 

 Selkirks. The transverse valleys, noted by Dawson as extending into the 

 foot-hills and due to "causes not now apparent," probably mark the location 

 of drainage streams developed while the peneplain was being formed and antedate 

 the final upheaval of the region. That these valleys were occupied by extensive 

 glaciers, presumably in Pleistocene time, is everywhere evidenced by the 

 morainic accumulations, rounded rock contours, glaciated surfaces, extensive 

 plucking, truncation of mountain spurs,~amphitheaters, rock basins, and hanging 

 valleys. The valleys generally were filled with ice to a depth of 2,500 to 4,000 

 feet during the maximum period of glaciation, the height, as pointed out by 

 Wilcox, rarely falling below 7,000 feet above sea-level. Either because the 

 mountains were so completely enveloped in ice and snow, or because of the 

 nature of the final retreat, extensive terminal moraines were not formed in 

 the main valleys. Ground-morainic deposits, however, hundreds of feet 

 thick, occur in places favorable for their lodgment beneath the ice. Near 

 Banff, in the Bow and Cascade valleys, Wilcox discovered evidence of two 

 distinct till-sheets, the older highly charged with pebbles, with little clay, the 

 younger consisting mainly of very hard clay. 2 In the extension of the Bow 

 Valley to the eastward of the mountains, McConnell and Dawson found three 

 separate till-sheets. The lowest and oldest of these appeared to have been en- 

 tirely derived from the mountains and to pass eastward gradually into the 

 "Saskatchewan gravels" of the plains. For this formation Dawson suggested 

 the term "Albertan, " 3 which he regarded as of pre-Kansan Age. 



The upper two boulder-clays contained rock fragments of both eastern and 

 western origin, each variety preponderating in the direction of its origin, showing 

 a commingling of the deposits of the Cordilleran and Hudson Bay ice sheets. The 

 middle of the three till-sheets Dawson correlated with the Kansan and the 

 upper with the lowan (p. 509). In the light of our present knowledge the upper 

 would be referred to the Illinoian, which succeeded the Kansan in the upper 

 Mississippi Valley and was of much wider extent than the lowan. The corre- 

 lation of these sheets with those observed at Banff has not yet been made. 



c. Lakes. In the very interesting paper above referred to, Wilcox recog- 

 nizes four types of lakes in those portions of the Canadian Rockies which came 

 under his observation: 



First Lakes lying in depressions of the valley drift, often in chains of 



i Harriman Alaska Expedition, vol. HI, Glaciers and Glaciation, Gilbert, p. 183. 



2 "A Certain Type of Lake Formation in the Canadian Rocky Mountains," Jour, of Geol., vol. vn, 

 1899, p. 249- 



"Note on the Glacial Deposits of Southwestern Alberta," Jour, of Geol., vol. HI, 1895, p. 510. See 

 also note on page 384, vol. in, Geology, by Chamberlin and Salisbury. 



