ALATNA RIVER 567 



is an angular block of granite more than 10 feet in shortest dimension, 

 perched on exposed schist bedrock in such relations that it could only 

 have been brought and deposited by a glacier heading in essentially the 

 same region as the existing glaciers and of at least five times as large 

 size. 



Truncated spurs with triangular facets and steep slopes form the 

 characteristic features in tlie upper Alatna Valley. In the central part 

 of the Alatna Valley, l^ake Takahoela marks a glacially overdeepened 

 part of the old valley, and the ridge separating the lake from the river 

 shows well-marked lea and stoss slopes developed on the roches moun- 

 tonnees. The wh'ole form of this part of the valley shows that it has 

 been caused by a larger agent than running water, and has then been 

 partly filled in so that the existing streams show patterns discordant 

 with that of the valley. 



Some ice from drainage basins now separated from the Alatna entered 

 the latter valley during the maximum period of glaciation. Thus Men- 

 denhall notes that the pass between the Keokuk and the Alatna was occu- 

 pied by ice, and he states : 



"Along Help-me-Jack Creek, in the Middle Alatna Valley, drainage changes 

 have taken place that are best explained by glacial action. The direct topo- 

 graphic continuation of the Upper Help-me-Jack Creek Valley is eastward into 

 the Alatna by the pass which leads to the latter stream in the vicinity of Rapid 

 City, but Help-me-Jack Creek at present leaves this broad open way, turns to 

 the south at right angles to its logical course, and reaches the Alatna at 

 Beaver City. Such a course probably was originally a spillway for glacial 

 waters, and in it Help-me-Jack Creek became intrenched while the more 

 northerly outlet was still occupied by ice." ^ 



Another pass to the east of the main Alatna Eiver, near Lake Taka- 

 hoela, served also as a spillway for both ice and water. This place is 

 picturesquely known by the natives as Akabloouk, which means "day- 

 light through the hills.^^ It is a broadly open saddle, with an elevation 

 of about 400 feet above the Alatna, and was formerly occupied by a drain- 

 age diverted to Malamute Eiver, a tributary of the Alatna, when south- 

 ward drainage was obstructed by the Help-me-Jack or Takahoela gla- 

 ciers. The details, however, of the glacial and post-glacial history have 

 not been worked out and many of the stages are obscure. 



NoATAK Basin 



In the high hills at the head of the Noatak are many small glaciers 

 similar in general character to those in the Alatna Valley. None of these 



' W. C. Mendenhall : Professional Taper No. 10, U. S. Geol. Survey, p. 40. 

 XL — Bull. Geol. Sqc. Am.^ Vol. 23, 1911 



