PLEISTOCENE DEPOSITS, GLACIATION. 85 



The John Valley till sheet extends across the divide by way of Anaktuvuk Pass 

 and is continuous with that of the Anaktuvuk Valley and the Arctic slope. At the 

 pass the valley is 3 miles wide and open, and its surface is so flattened with infilled 

 drift that the small streams descending from the mountains in this locality are 

 deflected by the merest obstacle to either side of the divide, flowing sometimes north- 

 ward by way of the Anaktuvuk to the Arctic, and at others southward to John River 

 and the Yukon. 



At the pass occur lakelets of glacial origin. One of these, Cache Lake (PI. X, J5), 

 just northeast of the divide, is 30 feet or more deep. Its surface lies about 100 feet 

 below that of the adjacent ground moraine, giving for the till sheet here a thickness 

 of at least 130 feet. Just south of the pass the till sheet formerly extended entirely 

 across the valley, as is shown by the flat-topped outlying remnants of ground moraine 

 in its middle. These rise to the height of more than 100 feet above the stream, 

 and accord in level with the ground-moraine terraces on either side. 



On the whole, the till sheet in this northern part of the range seems rarely to 

 extend up the side slopes to more than 500 or 600 feet above the floor of the valley. 

 Judging, however, from the rounded and sometimes relatively flat-topped aspect of 

 the mountains near the middle of the range (Pis. XIV, B 1 and XV, A), certain areas 

 were not only occupied by an ice cap, but the tops of some of the lower mountains 

 were planed off by ice movement. 



Naturally, the side valleys in this region were among the last to become free 

 from glaciers, some of which probably remained long after the disappearance of the 

 ice from the adjacent parts of main valleys. This is shown by the presence of rela- 

 tively fresh terminal moraines in the side valleys. Four miles northwest of the 

 middle of John River Valley the small valley of Contact Creek is crossed by such a 

 moraine. 1* is typical, being about 60 feet high and one-fourth of a mile in length, 

 measured parallel with the valley. A similar but older feature occurs in John River 

 Valley, near the middle of the range, about 12 miles in direct line south of the sixty- 

 eighth parallel. Here the valley flat is crossed by a terminal moraine about 60 feet 

 high, a portion of which is shown in PI. XV, B. It still forms a continuous ridge or 

 dam across the valley, except where the river has cut a notch-like passage, 200 yards 

 wide, at the left. At the right the moraine seems to be continuous with the till sheet, 

 which is 10 to 20 feet thick, and rests on the bed-rock benching at a height of about 

 100 feet above the river. As seen in looking parallel with the valley, the ridge 

 presents an undulating profile and is sharp-crested, owing to its upstream side being 

 cut away by the river. Though it exhibits but little of the typical hummock-and- 

 kettle topography of a terminal moraine, it is composed mainly of typical bowlder 

 clay carrying striated pebbles and bowlders, some a foot or more in diameter. The 

 materials noted are of the same constitution as those of the river gravels, there being 



