ICE AGE IN NORTH AMERICAN ARCTIC — FLINT 249 



and the melting of fallen snow during the summer diminished. All 

 of this, quite understandably, resulted in the enlargement of glaciers 

 existing in the higher mountains and in the appearance of many new 

 glaciers in mountainous districts. There can be little doubt that in 

 Arctic North America the first crop of glaciers took form in the two 

 great mountain regions : the Alaska- Yukon region and the Greenland- 

 Ellesmere Island-Baffin Island-Labrador-Quebec region. 



The probable growth of the glaciers in the Alaska- Yukon region is 

 not difficult to trace. Individual mountain glaciers enlarged, thick- 

 ened, and coalesced. Many of them spread out beyond the bases of 

 the mountains as piedmont glaciers. In southern Yukon and north- 

 ern British Columbia the ice bodies flowing eastward from the Coast 

 Eanges and those flowing westward from the Rocky Mountains 

 coalesced over the rough but somewhat lower country between them, 

 and the combined mass thickened and grew into an ice sheet that 

 nearly overtopped the high mountains themselves. Geological evi- 

 dence shows clearly that the ice, when near its maximum extent, flowed 

 from the lower interior country westward across the higher coastal 

 mountains to the Pacific. 



The growth of the glacier ice in the eastern part of the continent is 

 less clearly evident, but the probable course of events was similar. 

 Through the use of what scanty direct evidence we have, and by 

 analogy with better-known regions, we can conjecture that on each 

 of the highlands along the northeastern border of the continent proper, 

 and in Greenland, the new crop of glaciers expanded until they coa- 

 lesced, as did those in the far west. Recent seismic measurements, by 

 the Expeditions Polaires Franchises, of the bedrock surface beneath the 

 Greenland Ice Sheet have suggested the possibility that the land mass 

 of Greenland consists of three separate islands which have been buried 

 beneath the Greenland Ice Sheet. 



Glaciers descending the western slopes of the mountains of Elles- 

 mere and Baffin Islands, and of Labrador and Quebec, formed a pied- 

 mont apron of ice that chilled the air above it and thus drew snowfall 

 from the comparatively moist air masses that approached it from the 

 south and southwest. The added snowfall increased the thickness of 

 the ice, which thereby gradually became a topographic barrier to the 

 southerly and southwesterly winds, as well as a cold- air barrier or 

 polar front. Snowfall was thereby still further increased, which in 

 turn thickened the ice and increased its outward spread. 



The high cold front of the combined glacier crept slowly westward 

 and southward, fed by moisture brought to it by the winds it inter- 

 cepted. At the same time the ice thickened until it buried, or nearly 

 buried, the highlands along the northeast coast on which the earliest 

 glaciers had formed. The ice, now the full-fledged Laurentide Ice 

 Sheet, flowed across the broad, shallow Hudson Bay depression and 



