1855.] ISBISTER NORTH AMERICA, ETC. 509 



son has detected it in the hollows of the granitic plateau, and he ex- 

 presses 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 has 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 Saskatchewan and Elk 

 Rivers. The canoe-route does not touch upon this river, which has 

 its outlets in one of the south-western arms of Lake La Crosse ; but 

 it is 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. 



The Elk River, the most southerly feeder of the Mackenzie, ori- 

 ginates in the Rocky Mountains, as already stated, near the 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 Mississippi 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 pre- 

 cipitous descent of 650 feet, disclosing a deep layer of sand, enclosing 

 masses of sandstone, of about 600 feet in depth ; the whole reposing 

 upon an extensive formation of limestone which lines the whole bed 

 of the Clear-water as far as its junction with the Elk River. The de- 

 posits of sand and sandstone alternate with thick beds of bituminous 

 shale, in some parts more than 150 feet in depth. These bituminous 

 deposits form the distinguishing feature of the formation now under 

 notice, and are developed to an enormous extent, having been traced 

 at intervals along the whole length of Mackenzie River as far as the 

 shores of the Arctic Sea. Springs and pits of fluid bitumen are of 

 common occurrence, and along the banks of Elk River in particular 

 the shale beds are so saturated with this mineral as to be nearly 

 plastic. The whole formation bears a decided resemblance in its 

 lithological character to the lower members of the " Erie Division " 

 of the United States' geologists, which M. de Verneuil considers to 



2 M 2 



