90 RECONNAISSANCE IN NORTHERN ALASKA IN 1901. 



No glacial drift was noted on the top of Lookout Mountain, and. as the surface 

 was deeply snow covered at the time it was visited, the elevation to which the drift 

 ascends on its slope could not be learned. Southward, on the northeast side of the 

 lower AJatna Valley, what seem to be till terraces occur along the south side of 

 Double Mountain up to a height of 1,000 feet. 



Just below the mouth of the Alatna the right bank of the Koyukuk presents a 

 steep-faced exposure of ckvv and gravel, rising 80 to 100 feet above the river." The 

 lower 50 feet of this section seems to be till, and is distinctly separated by a well- 

 defined contact from the upper portion, which consists mostly of gravels and silts, 

 some of which are discordantly stratified. 



From the character of the topography glacial drift is supposed also to occur on 

 the opposite side of the Koyukuk and to extend southward toward the mouth of 

 Kanuti River. Mr. Mendenhall reports that in the country lying north of this 

 region, on the upper waters of the Alatna and the Kowak, above the sixty-seventh 

 parallel there is evidence of glaciation similar to that in the same latitude on John 

 River. Furthermore, in the recent gravels along the Koyukuk near Bergman, 

 notably on the south side of the river, there are large granitoid bowlders, totally 

 foreign to the country rock of the region. These may have been brought here 

 through the agency of river ice from far up the valley of South Fork, but it seems 

 equally probable that they may have been brought by glaciers from the mountains 

 to the north where similar rocks in place are known to occur. 



The hill just west of Bergman consists of Bergman sandstone, but on its slope, 

 at a height of nearly 200 feet above the river, there is a gravel deposit composed of 

 heterogeneous materials. An examination, as thorough as could be made under 

 unfavorable conditions, indicates that ice action was concerned in its origin. It con- 

 tains characteristically angular and subangular ice-worn pebbles, with polished sur- 

 faces, often profuselj 7 striated. The strise are of distinctly glacial origin and can in 

 no wise be ascribed to the action of river ice. 



From the above-enumerated observations in this southern part of the field it is 

 inferred that glaciation extended from the mountains southward into the Koyukuk 

 Basin across the Arctic Circle and beyond Bergman, but observation has not been 

 sufficient to determine whether this extension was in the form of a continuous ice 

 sheet, or merely as vallej^ glaciers. From topographic criteria, however, it seems 

 probable that most of the hills below 2,000 feet were covered by ice or neVe, while 

 such peaks as Mount Lookout and its higher fellows appeared as nunataks above its 

 surface, and that glacial activity, or ice work, was largely restricted to the valleys 

 and lower reaches of the hill slopes. 



In the John River and Anaktuvuk River portions of the Endicott Mountains the 



a This bluff is the Unatlotly of the natives. 



