52 RECONNAISSANCE IN NOBTHEBN ALASKA IN 1901. 



A profile and geologic section appearing on PI. III. drawn on the same scale 

 as tlu' map. illustrate the structural features ami relations of the various rock 

 formations. It extends from the southern edge of the map al A (PI, III) to 

 the foot of the Colville delta and the Arctic coast at .1. In order to show the 

 structure in the Tertiary coastal plain and to represent the Hats and delta near sea 

 level at the north, the scale of the section has been vertically exaggerated 5:1 as 

 compared with the horizontal scale, and in order to represent more accurately the 

 relations of the rocks as actually observed the section follows the somewhat zigzag 

 line of traverse. Where it traverses the rocks diagonally, as in the northern 

 edge of the Fickett series, compensation has been made therefor by reducing the 

 dips of the rocks in the section. As the line of traverse follows the vallej-s, where 

 the topograph}- has been reduced by erosion, the profile rarely rises to the normal 

 height of the adjacent land mass. Consequently the peneplain feature of the Endicott 

 Mountain summits is not expressed by the profile. From studies thus far made of 

 the section it promises to be of far-reaching importance, not only in deciphering the 

 geology of Alaska, but also in making correlations with Asiatic stratigraphy. 



Near the northern edge of the range, as shown on the map, the section traverses 

 the mountains to the east of the Anaktuvuk Valley, but as the rocks have here been 

 disturbed by folding and faulting, a supplementary short profile section (fig. 4), show T - 

 ing the rocks as the}- appear on the west side of the valley, has been introduced. It 

 extends from the Lower Carboniferous at Contact Creek on John River a distance 

 of about 25 miles northeastward across the Devonian, along the north side of 

 Anaktuvuk Pass, to the Cretaceous of the Anaktuvuk Plateau on the west of 

 Anaktuvuk River. The base of this section represents approximately the elevation of 

 the floor of the Anaktuvuk Valley and that of the pass, which is about 2,500 feet. 

 The mountains rise to about 5,500 feet. Besides the faulting shown between the 

 Devonian and the Lower Carboniferous on the south, and in the Devonian itself 

 toward the north, the section supposes the Lower Cretaceous to be resting uncon- 

 formably on the upturned and eroded Devonian. 



OUTLINE OF GEOLOGIC HISTORY. 



The rocks composing the section here considered, extending geographically from 

 the sixty -sixth parallel to the Arctic coast, a distance of nearly 400 miles, comprise 

 representatives of most of the geologic ages ranging from Silurian to Recent, as 

 shown in the accompanying table. 



