174 PHYSICAL GEOGRAPHY. 



direction, drains seventeen degrees of latitude into the 

 Arctic Sea, taking its course through a valley which 

 differs in its character from that of the Mississippi, as the 

 details of progress of the expedition through it have 

 already shown. In this place it will be sufficient to 

 recall to mind that from Methy Portage (Portage la Loclie) 

 to the sea, a distance of 1,400 geographical miles, the fall 

 is about 900 feet, the successive portions of the river being 

 designated the Washacummow, Elk or Athabasca, Slave, 

 and Mackenzie Rivers. 



Two other rivers of magnitude cross the Arctic circle, 

 viz., Back's Great Fish River, which, originating near 

 Great Slave Lake at an altitude of 150 feet above its 

 surface, runs east-north-east into the Arctic Sea, draining 

 the north-eastern corner of the continent ; and the Yukon, 

 which, rising to the westward of the Rocky Mountains, 

 not far from the union of the Francis and Lewis, which 

 form the Pelly, flows first to the north, and after receiving 

 a large tributary named the Porcupine, to the westward, 

 falling into Beering's Sea, where it is known to the 

 Russians by the name of the Kwichpack. 



A glance at the map will show, that on the eastern side 

 of the continent the water basins generally maintain the 

 north-easterly inclination of the Alleghanies, while further 

 to the westward the basins of the two great rivers assume 

 a parallelism to the Rocky Mountains ; and that the in- 

 fluence of the intermediate hypogenous formation has been 

 of a different character, the rivers winding their way across 

 it, sometimes with a southerly, sometimes with a northerly 

 inclination, seemingly indicating the obstruction offered by 

 the harder rocks to the agent by which the river channels 

 were excavated. On emerging from the belt, the lower 

 parts of the rivers generally incline towards the north-cast, 



