568 p. S. SMITH GLACIATION IN NORTHWESTERN ALASKA 



was examined in detail, and as heavy fog masked the highest hills all 

 the time we were in this region, those seen were probably only a few of 

 those actually there. Although of no great size, the varied forms, from 

 steep cliff glaciers to massive domes of snow and ice, add much to the 

 picturesqueness of the scener}^ in the headwater region. Many of the 

 unexplored side valleys tributary to the N"oatak farther down stream 

 seemed promising places to look for existing glaciers, but none was seen 

 west of longitude 157. 



Evidence of past glaciation and glacio-iiuviatile conditions are abun- 

 dant throughout the ISToatak basin. In fact, the main source of danger 

 in canoeing was due to the great boulders derived from the enormous 

 outwash deposits of glacio-fluviatile origin that have been transected by 

 the river. Boulders of all sizes, from hundreds of tons down, were 

 found, some in the river and others just emerging from the gravel de- 

 posits. These large, glacially transported boulders seemed in the main 

 to have been derived from the tributary valleys and not to have come 

 from the valley of the main stream. 



The deposits in which they occur were in the main of water-rounded 

 and assorted material, with stratification usually more or less evident. 

 The outwash deposits form broad gravel plains rising a hundred or more 

 feet above the river. On the upland surface of these flats are lakes at 

 many places but slightly incised below the general level. Figure 2, 

 plate 35, shows a portion of the N'oatak Valley where one of these up- 

 land lakes has nearly been drained by the lateral erosion of the stream 

 when it was slightly above the level of the present N'oatak, which appears 

 to the right. The gravel bluffs here are about 100 feet high, but out- 

 wash deposits of well worn gravels near this place have been traced up 

 to an elevation of about 900 feet above the river. 



The canyon of the Noatak is another of the features that is probably 

 in a measure connected with the glacial and glacio-fluviatile history of 

 the region. The river at this place has abandoned a well opened out 

 valley and has cut a narrow gorge 3 miles long from 500 to 700 feet 

 deep across a former spur of hard rocks. Plate 36 shows the topography 

 in the vicinity of the canyon. The former valley, now occupied by lakes, 

 •J in the background, with the present canyon partly visible in the fore- 

 ground. A large stream joins the Xoatak a short distance below the 

 canyon, and the cause of the diversion is believed to have been the ad- 

 vance of a glacier down this valley and the blocking of the former course 

 of the N"oatak by ice deploying from this valley. The canyon is dis- 

 tinctly a feature carved by running water, and was not eroded by ice, so 

 that the explanation of its origin assumes that the waters impounded 



