PLEISTOCENE DEPOSITS, GLACIATION. 87 



of the mountains the river bluff on the left exposes a thickness of a little over 100 

 feet of typical till. From this point the deposit continues laterally up the side slopes 

 of the valley, and apparently overspreads the plateau indefinitely, while the lower 

 portions of the deposit, extending downstream, form terraces along the river. At 

 about 10 miles from the mountains and 2£ miles east of the river, at an elevation of 

 5,400 feet, or nearly 700 feet above the valley floor, the top of a rounded sandstone 

 hill, which rises to the general level of the plateau, bears patches of till a foot or 

 more in thickness. Here, too, some of the less firm portions of the bed rock have 

 been disturbed, while others bear markings that have been interpreted as imperfect 

 glacial stria?. These trend approximately parallel with the valley. A view of the 

 surface of the plateau from this point, as shown in PI. IV, seems to indicate the 

 presence of drift almost everywhere, though the deposit is probably thin on the tops 

 of the higher ridges. 



Till occurs farther down the AnaktuTuk, forming terraces and moraines similar 

 to those noted in the intramontane section of the valley. About 15 miles north of 

 the mountains, just below camp July 1, on the side of the valley, there is a 

 lateral moraine that rises to a height of about 150 feet above the valley flat, which is 

 here about three-fourths mile wide. The steep angle, 45° to 60°, at which the drift 

 materials lie, as exhibited in the face presented to the valley, clearly denotes that 

 they were deposited largely against an ice wall. Just in front of this moraine is a 

 characteristic overwash plain from whose upper edge an unquestionable terminal 

 moraine extends indefinitely, both to the east and to the west, away from the valley. 



A little north of the above region, about 23 miles from the mountains, occurs the 

 first pronounced cross ridge of Lower Cretaceous beds, through which the river has cut 

 a short canyon. A few miles east of the river this ridge attains an elevation of about 

 2,500 to 2,600 feet. On ascending the ridge in this vicinity, from the plateau on the 

 south, the till sheet was found to continue up to the elevation of about 2,250 feet, 

 where, on the slope becoming a little steep, it suddenly ceases and the bed rock 

 becomes exposed and continues so across the broad top of the ridge, while till is again 

 encountered on its north slope, which descends into Willow Creek Valley. 



On the top of the above ridge, however, are glacial erratic bowlders, which, 

 though not abundant, are decisive in showing that an ice sheet passed over the ridge. 

 As these erratics occur 400 to 500 feet above the ground moraine, it is inferred that 

 they were probably transported as englacial or superglacial material. Here, also, 

 large blocks of bed-rock sandstone have been moved from their original position to 

 an extent that can not be accounted for by frost or weathering, so that their trans- 

 portation seems to have been the work of moving ice. 



About 10 miles northward, on Willow Creek Ridge, a similar feature, no glacial 

 drift was found. At a few points the edges of the sandstone beds are disturbed, as 



