110 I. (. RUSSELL 1 RFACE GEOLOGY OF ALASKA. 



seen for several miles along the river, both above and below it. They were 

 observed also on the Porcupine river, nearly due north of the locality here 

 mentioned. 



[mmediately at the international boundary there are bold bluffs on each 

 Bide of the river, with mountains about 3,000 feet high rising hack of them. 

 The ranges are serrate, trend nearly east and west, ami are composed of 

 limestone in nearly vertical strata. The river follows the south base of one 

 of these limestone mountains for fully fifty miles east of the boundary. As 

 i from the river, this range seemed to be monoclinal in structure. 



Near Forty-mile creek, and from there a long way up-stream, the banks 

 are in general of metamorphic schist with quartz veins. The rocks form 

 bold pinnacles and headlands along the river, leaving no room for a flood- 

 plain at their bases. 



My notes on the rocks of this region are meagre, owing to the lack of 

 opportunities for personal examination on shore, aud I have withheld much 

 that I Hotel concerning the " hard geology," fearing that my hasty observa- 

 tion- might be too much in error to be of value. 



■- 



Geology of the Yukon River. 



the delta of the fukon. 



(,■ ieral C'ltarnctrr. — The delta of* the Yukon, as shown by such examina- 

 tions as have been made, is about L25 miles in length, the apex being where 

 the river first divides on approaching its mouth. The periphery of the 

 delta, n >t including minor sinuosities of the shore-line, is approximately 150 

 miles. This embraces, however, some highlands, which rise like islands in 

 the broad, nearly level expanse of sediment that has been spread out by the 

 river. 



I fire! saw the delta near the entrance to the Aphoon branch. This is 

 the most northerly channel by which the Yukon discharges into the sea. 

 The land is there low and swampy, and iutersected by muddy sloughs and 

 tide-waye li is bare of trees, but covered by a most luxuriant growth of 

 mosses aud lichens. The meadow-like expanse is dotted everywhere with 

 ponds ami lakeht.-. This i> a pail of the -real tundra bell that skirts the 

 entire northern and western Bhorea of Alaska, the characteristic features of 

 w hieh : ■ i il» d i l.-i w here in this paper. 



Drift Timber. The border of the delta and the hanks of the numerous 

 water channels thai intersect itare fringed with drift-wood. Debris of similar 

 character i- exposed in such abundance in freshly formed river escarpments 



to i ■• no .dent thai the cut ire delta contains a more or less continuous 



Bubstratum of trunks, branches aud roots of trees, embedded in river >ilt. 



