160 ALASKA AND ITS MINERAL RESOURCES 



river just below Dease lake, which may belong to the older 

 granites, though they do not make the same distinction that 

 Spurr does between the older granites and the later intrusive 

 rocks. 



Rocks of the various gold-bearing series above the granite are 

 reported at the following localities : Their first appearance, to 

 one ascending the Yukon from the sea, is near the mouth of the 

 Nowikakat. From here up to the Tanana river, rocks of the 

 Birch creek series outcrop frequently along the river, when not 

 concealed by Tertiary sandstones and conglomerates, and the 

 range of low mountains on the north side and parallel to the 

 river is probably formed of these and Fortymile rocks. About 

 three miles above the mouth of the Tanana, granite is exposed 

 on an island in the Yukon, and 12 miles higher calcareous 

 quartzitic schists of the Fortymile series appear under the Ter- 

 tiary conglomerates. From the mouth of the Tanana up to 

 Fort Hamlin, at the lower end of the Yukon flats, the river 

 runs in a canyon-like channel, known as the Lower Ramparts, 

 cut through a low range of mountains, which consist principally 

 of the dark greenish and reddish rocks of the Rampart series, ex- 

 cept where these are buried under Tertiary conglomerates. The 

 latter rocks occur immediately above the exposures of Fortymile 

 rocks, and again from Mynook creek up beyond the mouth of 

 Hess creek. Higher up on these streams the Rampart rocks come 

 to the surface, and the Fortymile rocks are supposed to be un- 

 covered at their very heads. Between the two areas of Tertiary 

 rocks the Rampart rocks occupy a belt 15 to 20 miles wide along 

 the river, and are cut by great dikes of intrusive granite. 



From Fort Hamlin up to near Circle City, a distance, neglect- 

 ing curves, of about 200 miles, the river flows through a perfectly 

 flat region covered by fine silts and gravels, known as the Yukon 

 flats, in which no outcrops of solid rock have been observed. In 

 the Birch creek district, around the headwaters of Birch creek 

 and southwest of Circle City, the Birch creek series occupy a 

 broad area; their general strike is east and west, curving at 

 either end to the northward, and the prevailing dip is between 

 5° and 30° to the south. There is, however, evidence of a north- 

 ern dip as well, and the Fortymile schists and marbles rest upon 

 them along the trail to Circle City. Marbles, probably belong- 

 ing to the Fortymile series, are also reported in the hills between 

 Birch creek and the Tanana to the southward. 



At the crossing of Birch creek by the trail from Circle City and 



