103 



been enriched and in places contain gold in commercial 

 quantities. 



The White Channel bench or hill gravels are the oldest 

 in the district, and, excepting the present creek gravels, 

 are the most important from an economic standpoint. 

 They were originally creek gravels, deposited in a similar 

 manner to those at present occupying the low levels, and 

 their elevated position is due to an uplift which affected 

 the whole region bordering the Yukon from Stewart river 

 northwest to the Alaskan boundary and for a considerable 

 distance beyond. This uplift, and a slight depression 

 which preceded it, produced many notable changes in the 

 topography of the country. The White Channel gravels, 

 however, differ somewhat from the ordinary type of stream 

 deposit. They are very compact as a rule, and in some of 

 the hydraulic cuts stand up in almost vertical cliffs, even 

 when the face is unfrozen. The white or light gray color- 

 ation from which these gravels derive their name, is very 

 conspicuous in most of the sections, but is not universal, 

 as red, yellow, and dark gray beds frequently occur. The 

 deposit is highly siliceous, the principal constituent con- 

 sisting of rounded pebbles and rounded and subangular 

 boulders of vein quartz. Flat schist pebbles and boulders, 

 usually in a more or less advanced stage of decomposition, 

 occur with the quartz, as also do occasional pebbles derived 

 from the various dikes and stocks outcropping along the 

 valleys. The pebbles and boulders seldom exceed 18 inches 

 (.5 m.) in diameter, and are embedded in a compact 

 matrix consisting essentially of small sericite plates and 

 fine angular quartz grains. A few large angular blocks 

 from 3 to 4 feet (.9 to 1.2 m.) in diameter occur in places 

 but are rare and generally near bedrock. 



The White Channel gravels are strikingly uniform in 

 composition and general character, and as a rule the bedding 

 planes are inconspicuous. Their range in thickness is from 

 a few feet to 150 feet (1 to 45 m.), and the original width 

 from 200 yards to over a mile (180 m. to over 1.6 km.). 

 Unlike the creek and gulch gravels they appear to be des- 

 titute of vegetable and animal remains. 



In places the typical compact variety of the white 

 Channel grave s is replaced toward the sides of the old 

 valley by flat rusty coloured gravels, more loosely bedded 

 and containing a smaller proportion of quartz than the 

 ordinary white variety. These probably represent flood 

 plain deposits and are seldom productive. 



