SUPERFICIAL GEOLOGY OF BRITISH COLUMBIA. 123 



9. If the north- to-south glaciation has been produced by glacier- 

 ice, it must have been either (a) by the action of a great northern 

 ice-cap (against which grave difficulties appear), or (b) by the 

 accumulation of ice on the country itself, especially on the moun- 

 tains to the north. In either case it is probable that the glacier 

 filled the central plateau, and, besides passing southward, passed 

 seaward through the gaps and fjords of the Coast range. The 

 Boulder-clay must have been formed along the front of the glacier 

 during its withdrawal, in water, either that of the sea, or of a great 

 lake produced by the blocking by local glaciers of the whole of the 

 valleys leading from the plateau, to a depth of over 5000 feet. 



10. If general submergence to over 5000 feet be admitted, the 

 Japan current would flow strongly through Behring's Strait, and 

 over part of Alaska, while arctic ice-laden water, passing south 

 across the region of the Great Plains, would also enter the central 

 plateau of British Columbia, accounting for the north-to-south 

 glaciation and simultaneous formation of the Boulder-clay. 



EXPLANATION OF PLATE V. 



Outline Map of British Columbia, showing the portions exceeding an elevation 

 of 3000 feet above the sea-level, the general direction of the principal 

 mountain-ranges, and the former extension of glaciers from the Coast 



Mountains. 



