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In the larger view, the Canadian Cordillera may be 

 broadly divided into four provinces: (a) the Rocky 

 Mountain system; (b) the Middle or Interior ranges, 

 including the Purcell, Selkirk, Columbia and Cariboo moun- 

 tains; (c) the Belt of Interior Plateaus; and (d) the 

 Coastal system, including the Coast range, the Cascade 

 range, and the Vancouver-Queen Charlotte range. The 

 first, third, and fourth of these provinces extend, with but 

 minor interruptions, through Yukon Territory and Alaska 

 to Bering Sea. The Middle ranges as a whole are specially 

 broad in southern British Columbia, but narrow rapidly 

 to the northward and, in the United States, have been 

 broadly depressed and covered by the lava floods of Idaho 

 and Washington states. 



GLACIATION OF THE CORDILLERA. 



The field habit of the visible glaciated rock-surfaces 

 and the condition of the drift deposits, in these Canadian 

 mountains, strongly suggest that the great glaciers of the 

 Cordillera were essentially contemporaneous with the 

 eastern ice-cap at its Wisconsin stage. No facts yet 

 determined on the mainland of British Columbia or in 

 Alberta have shown clearly that general Pleistocene 

 glaciation was multiple. It is true that, at many points 

 within the Cordillera and along its piedmonts, younger 

 till rests on water-laid silts, sands, or gravels of Pleistocene 

 age; but this relation is that normal to the inevitable 

 oscillation of ice-fronts during a single glacial period and 

 it is still unsafe to postulate a general interglacial epoch 

 for the Cordillera. However, further investigation of its 

 interior portion may demonstrate one or more interglacial 

 periods, even in spite of the fact that, in a topography 

 so strongly accidented, a more recent glaciation must 

 tend to obliterate the traces of an earlier one. 



When at their maximum, the Pleistocene glaciers 

 of the mainland formed an interior ice-cap flanked by 

 double rows of valley glaciers. The ice-cap was fed by the 

 local sheets respectively draining the western versant of 

 the Rocky Mountain system and the eastern versant of 

 the Coast range. The eastern slope of the Rockies was 

 drained by many large valley glaciers. These often 

 became confluent as piedmont sheets on the plains of 



