PLEISTOCENE DEPOSITS, GLACIATION. 89 



to hare been confined substantially to the present drainage ways, in the form of valley 

 glaciers, of which that of the Anaktuvuk is the chief. 



There is evidence that the Anaktuvuk glacier extended northward to the sixty- 

 ninth parallel, and there are some indications that it may possibly have extended 30 

 miles farther, to within 10 or 12 miles of the present mouth of Anaktuvuk River, 

 but it is not to be supposed that it crossed Colville River, if indeed it ever reached 

 it. This latter statement is probabl}- also true of the ice streams to the west that 

 must have occupied the valleys of Ninuluk, Killik, Kurupa, and Kucher creeks, 

 which enter the Colville a little north of the sixty-ninth parallel. 



It does not seem probable that the drift sheet on the Arctic slope much exceeds 

 150 feet in thickness at any point. It apparent^ attains its maximum development 

 in the valleys, not far from the mountains, the source of supply. Elsewhere on the 

 slopes its surface seems to conform very largely to the preexisting topography of 

 the underlying terranes. 



In the southern part of the Endicott Mountains, evidence of glaciation, as has 

 been shown, may be found up to an elevation of nearly 2,000 feet. From the point 

 where John River leaves the mountains, southward to the region of Kanuti River, 

 the Koyukuk Valley region exhibits a generally rounded topography, which suggests 

 former glaciation, up to a height of 1,600 or 1,800 feet. On John River, near the 

 base of the mountains, the drift, so far as observed, is essentially till. In some 

 localities the deposit is at least 100 feet thick, and is marked by several terraces that 

 rise successively from the river to the southeast, above which the surface continues 

 to have a rolling, apparently ground-moraine topography, that finally gives way to 

 low, rounded mountains or hills, which also are supposed to be glaciated. 



Observations in the above region away from the immediate route of travel were 

 very limited. Along the route, however, glacial drift seems to be more or less 

 continuous all the way down the open flats of John River Valley, as is shown by the 

 topography and by occasional exposures of till rising to a height of 30 or 40 feet 

 above the river or resting in thinner sheets on the bed-rock benches at elevations of 

 from 30 to 100 feet above the stream. 



Till is present near the mouth of John River and on the right or west bank of 

 the Koy ukuk between Bettles and the mouth of Jane Creek, where it forms bluffs about 

 100 feet high. Similar conditions seem to prevail to the eastward, in the region of 

 Gold Bench-' on South Fork, whence they apparently continue northeastward across 

 the divide into the Chandlar River Basin, where till deposits similar to those on John 

 River have been noted in a previous report, and have since been observed to extend 

 up Granite Creek. 6 



"When the only opportunity for making observations at Gold Bench was presented, 5 feet of snow lay on the ground. 

 b Reconnaissance along the Chandlar and Koyukuk rivers, Alaska: Twenty-first Ann. Rept. U. S. Geol. Survey, pt. 2, 

 1900, p. 478. 



