56 BE00NWAISSA1T0E IX NORTHEBN ALASKA IN 1901. 



oast and west, parallel with the trend of the range. They are nearly all traversed 

 l>v the dominant jointing of the range, which cuts the rocks in a direction about 

 northeast-southwest, with dip nearly vertical or inclined steeply to the northwest, at 

 angles of 75° to 80°. There are also usually one or more sets of secondary jointing or 

 minor structure, trending in general northwest-southeast, sometimes approximately 

 at right angles to the major jointing. 



The above statement of the structures affecting the Paleozoics in the range 

 applies also in a limited way to the upland Mesozoics on either side. 



With the exception of the greenstone-schists occurring in the Totsen series, the 

 Paleozoics of the range, as well as the younger formations of the Arctic slope, are 

 all sedimentary, and, so far as observed, are relatively if not wholly free from 

 association with igneous rocks of any kind. 



SKAJIT FORMATION (UPPEK SILURIAN). 



Character and occurrence. — The Endicott Range, as noted, has two distinct axes, 

 of which the southern seems to be composed of the older rocks (see PI. Ill), those 

 of the Skajit formation and the Totsen series, the former playing the principal part. 



The rocks of the Skajit formation (PI. IX, B) consist of heavy-bedded crystal- 

 line limestone and mica-schist. Weathered surfaces, parallel with the bedding and 

 planes of movement and crushing, present a silvery sheen, due to the presence of 

 mica, while some layers grade wholly into mica-schist. On a fresh fracture surface 

 the limestone is found to be highly crystalline, generally fine or medium grained, 

 and of impure white or bluish-gray color, the latter apparently denoting the more 

 dolomitic phases of the rock. It weathers to a dirty gray or light brown, sometimes 

 tinged with red. > 



The formation occurs in the southern part of the Endicott Mountains, where, in 

 latitude approximately 67° 30', it occupies a belt that is from 15 to 20 miles wide, 

 in which the mountains rise to an elevation of more than 5,500 feet above sea 

 level, the rocks forming some of the highest peaks and most rugged topography of 

 the southern axis of the range. Judging from the attitude or prevailing dip of the 

 rocks and their extent measured across the strike, the formation probably has a 

 thickness of at least 4,000 feet. 



Structure.— The Skajit formation has a nearly east-west strike, parallel with 

 the general direction of the mountains; but about 20 miles west of John River this 

 trend changes to north of west. The structure in general indicates a broad anti- 

 clinorium whose middle part is occupied by a broad, shallow syncline. In general 

 the dips are gentle, as shown in PI. IX, B and PI. X, A. The latter shows the 



aThe term Skajit is of native origin, and is taken from a group of rugged mountains occurring within the area of the 

 formation to the east of John River. 



