101 



A section across the valley of any of the gold-bearing 

 streams entering the Klondike shows a comparatively 

 narrow, trough-like depression below, 150 to 300 feet 

 deep (45 to 90 m.), bordered on one or both sides by wide 

 benches beyond which the surface rises in easy, fairly 

 regular slopes up to the crests of the intervening ridges. 

 The benches represent fragments of older valley bottoms 

 partly destroyed by the excavation of the present valleys. 

 Narrow rock-cut terraces occur at intervals between the 

 level of the old valley-bottoms and the present level. 

 Auriferous gravels occur on the present valley-bottoms, 

 on the portions of the old valley-bottoms still remaining, 

 and on the rock terraces cut into the slopes connecting 

 them. These deposits may be classified as follows. — 



[Gulch gravels 

 Low level gravels<{ Creek gravels 

 [River gravels. 

 Gravels at intermediate levels. Terrace gravels. 

 High level /Klondike gravels 

 bench gravels \ White Channel gravels. 



The low level creek gravels are the most important 

 gravels in the district, and floor the bottoms of all the 

 valleys to a depth of 4 to 10 feet (1-2 — 3-0 m.). They 

 rest on a bedrock usually consisting of decomposed and 

 broken schists, and are overlaid by a sheet of black frozen 

 muck ranging in thickness from 2 to 30 feet (-6 to 9 m.) 

 or more. They are local in origin and consist entirely of 

 the schists and other rocks outcropping along the valleys. 

 The schist pebbles are usually flat, round-edged discs 

 measuring from 1 to 2 inches (25 to 50 mm.) in thickness 

 and from 2 to 6 inches (50 to 150 mm.) in length. These 

 pebbles constitute the greater part of the deposits, but are 

 associated with a varying proportion of rounded and 

 subangular quartz pebbles and boulders, and, less fre- 

 quently, with pebbles derived from the later eruptive 

 rocks of the region. The pebbles are loosely stratified, 

 usually embedded in a matrix of coarse reddish sand, and 

 alternate in places with thin beds of sand and muck. 

 These gravels frequently enclose leaves, roots and other 

 vegetable remains, and the bones of various extinct and 

 also existing types of northern animals, such as mammoth, 

 mastodon, buffalo, bear, musk-ox and mountain sheep. 



