* 
326 On the Geology of the Northwestern Regions of America. — 
rian formation attains probably a wider development in the 
Hudson’s Bay Territories than in any other part of the world in 
which its existence has been hitherto ascertained. Sir John Rich- 
ardson has detected it in the hollows of the granitic plateau, and 
he expresses a belief that it will be found to occupy all the 
valleys of that extensive district. 
Devonian Formation of the Elk or Mackenzie River.—The 
extent of the Silurian formation of Lake Winipeg northward 
as not been accurately ascertained. Limestones very similar in 
character have been traced on Beaver River, the most westerly 
feeder of Churchill River, and situated midway between the Sas- 
katchewan and Elk Rivers. The canoe-route does not touch 
upon this river, which has its outlets in one of the southwestern 
arms of Lake La Crosse; but it ig observed that the country on 
entering Sandy Lake along the line of communication near this 
part suddenly changes its aspect. Banks of loam, sand, and 
rolled blocks of a fine quartzose sandstone are found along the 
channels of the rivers; and shortly after emerging from the 
granitic district through which the route lies for the greater part 
of the distance from Cumberland House to Fort Isle-a-la-Crosse, 
We come upon a formation of quite another character, occupying 
the basins of the Elk River and its affluent the Clear-water. 
northern sources of the Saskatchewan ; and its bed, which forms 
with that stream two sides of an equilateral triangle, with its 
base resting on the western edge of the crystalline plateau, is not 
separated by any marked ridge from the Saskatchewan prairie 
country, which appears to extend with little interruption as far 
as the next great tributary of the Mackenzie, the Unjigah or 
Peace River. It is separated from the Churchill or Mississippt 
River system, having its outlet in Hudson’s Bay, by the carrying 
place of Portage La Loche, a plateau of about ten miles in breadth, 
which forms the dividing ridge between the waters flowing into 
Hudson’s Bay and those flowing into the Arctic Sea. Portage 
La Loche has at its highest point an elevation of about 60 feet 
above the sources of the Churchill River system; but it presents 
on the side of the Clear-water River a sudden and precipitous 
descent of 656 feet, disclosing a deep layer of sand, enclosing 
masses of sandstone, of about 600 feet in depth; the whole re- 
posing upon an extensive formation of limestone which lines the 
whole bed of the Clear-water as far as its junction with the Blk 
River. The deposits of sand and sandstone alternate with thick 
beds of bituminous shale, in some parts more than 150 feet in 
- These bituminous deposits form the distinguishing. 
tures of the formation now under notice, and are developed to an 
enormous extent, having been traced at intervals along the whole 
