﻿1861.] 



HECTOR ROCKY MOUNTAINS, ETC. 



391 



The route of the Expedition starting from Lake Superior, after 

 crossing a spur of the eastern axis, traversed the northern part of 

 the plateau to the Rocky Mountains, and thence down the western 

 slope of the continent to the Pacific Ocean. 



The Mackenzie Biver, rivaling in its proportions the Upper Mis- 

 sissippi, breaks the apex of this triangle, escaping through the Bocky 

 Mountains to the Arctic Sea ; while the Saskatchewan and other 

 rivers of the southern British territory dilate into great lakes at the 

 western base of the Laurentian axis, through which they then escape 

 to Hudson Bay. 



The Laurentian axis of metamorphic rocks with its fringe of 

 Silurian strata may be considered as stretching from Western Canada 

 to the Arctic Ocean, near the mouth of the Coppermine Biver, in aN.W. 

 direction ; hut it sends off a spur, which encircles the western shore 

 of Lake Superior, and loses itself under the prairies of the State of 

 Minesota. 



Lake Superior and Lake Winnipeg, according to the surveys 

 of the Canadian Expedition, have nearly the same altitude of 

 600 feet above the sea, while the rocky district that separates them 

 has double that elevation, or 1300 feet, above the sea ; but this is in 

 many places increased to 1600 feet by the deposits of drift that will 

 be hereafter described. 



The highest point of the great plateau that is in British territory 

 is to be found when, at the base of the Bocky Mountains, that chain 

 is intersected by the 49th parallel of latitude, where it is elevated 

 4300 feet above the sea. If followed into the United States to the 

 south, it is found to reach a still greater elevation along the base of 

 the mountains, until it merges with the great table-land of Mexico, 

 which has an altitude of 6000 feet. Erom the above point of inter- 

 section to the nearest point of the Laurentian axis, which is a line 

 from near the source of Belly Biver in a N.E. direction to Cumber- 

 land House on the Saskatchewan, the distance in an air-line is over 

 500 miles, and the difference of elevation of these two points gives a 

 mean slope of 6 feet in the mile. The general level of the eastern 

 base of the Bocky Mountains also declines rapidly to the north ; for 

 in latitude 51° 9', at where the Bow Biver emerges on the plains, the 

 elevation is 3900 feet, and at where the Athabasca, the most southern 

 tributary of the Mackenzie, leaves the chain in latitude 53° 12', it is 

 only 3300 feet above the sea*. 



The slope of this plateau is, however, far from being uniform, but 

 is broken by steppes which have been formed by the erosion of 

 the surface of the country, and which indicate different grades in 

 the elevation of the continent during later epochs. These steppes 

 are boldly marked, sometimes increasing the altitude of the prairies, 



* As the Rocky Mountains are cut through by valleys almost to the depth 

 of the plateau on which they stand, this depression of the chain towards the 

 north has a remarkable influence on the climate in some localities, especially 

 mitigating the severity of the spring months by admitting the influence of the 

 mild climate of the western sea-bord at a time when the eastern part of the 

 continent in the neighbourhood of the great lakes is still icebound. 



