THE CANTWELL FORMATION 123 



fourths of an inch in diameter. From this exposure to the mountain 

 top, a vertical distance of about 1,100 feet, the rocks are dominantly 

 black shale with plant impressions, alternating with beds of massive 

 graywacke, in some places approximating a sandstone. Near the 

 eastern base of this mountain the carbonaceous, plant-bearing 

 shales were observed to carry 2- to 2^ -inch seams of impure lignitic 

 coal. For 2^ miles north of this point mashed conglomerate 

 alternates with dark-blue to black slate (resulting from the 

 metamorphism of the carbonaceous shales), some phases show- 

 ing a crinkly surface of satin-like luster. Many of the rocks here 

 might properly be termed schists, and the formation as a whole 

 presents a black aspect due to the widespread dissemination of 

 carbonaceous material. 



A traverse was carried up a stream farther eastward in the 

 Wells Creek area. Near the southern border of the formation, this 

 stream exposes closely folded beds of slate, graywacke, and con- 

 glomerate, all severely mashed, the conglomerate almost beyond 

 recognition. The slate is also badly crushed and slickensides are 

 prominently developed. For two miles above these outcrops the 

 formation seems about equally divided between slate, graywacke, 

 and conglomerate, the last two having suffered most from the 

 regional metamorphism, although much of the slate has a crinkled 

 surface, suggesting the intensity of the compression to which the 

 rocks were subjected. Throughout this extent the rocks are 

 steeply dipping and apparently vary from 80° N. to 80° S. In 

 places are crinklings and plications suggestive of sharp folding, 

 and many specimens of a peculiar, plicated phase of mashed con- 

 glomerate were observed in talus fans. The formation as a whole 

 is dominantly dark-grayish to black in color. 



East of the Wells Creek basin, the Cantwell is replaced by a 

 large intrusion of granitic character, forming a rugged mountam 

 range surrounding the Nenana Glacier. A few miles northeast of 

 the glacier, at the foot of Cathedral Mountain, the Cantwell appar- 

 ently appears again; this area was not directly accessible, though 

 observable with field glass and through the agency of glacially 

 transported specimens. The sediments here consist of dark-colored 

 slates and mica schists, the latter representing the coarser elastics 



