MOUNT RAINIER 



was once the cradle of a glacier, and that ice mass, 



giawing headward and deploying even as the Carbon 

 lacier does to-day, enlarged its site into a horseshoe 

 basin, a typical glacial cirque. The lake in the center 

 is a strictly normal feature ; many glacial cirques 

 possess such bowls, scooped out by the eroding ice 

 masses from the weaker portions of the rock floor ; 

 only it is seldom that such features acquire the sym- 

 metry of form exhibited by Crater Lake. The lake- 

 lets observed in the neighboring valley heads all of 

 which are abandoned cirques are of similar origin. 



As for the skeleton character of the dividing crests, 

 it will be readily seen to be the outcome of the headward 

 gnawing of opposing cirques. In some places, even, 

 the deploying process has attenuated the ridges suf- 

 ficiently to break them through. West of Crater 

 Lake is an instance of a crest that has thus been 

 breached. 



It is a significant fact that the empty cirques about 

 the Mother Mountains lie at elevations ranging between 

 4,500 and 6,000 feet ; that is, on an average 5,000 feet 

 lower than the cirques on Mount Rainier which now 

 produce glaciers. Evidently the snow line in glacial 

 times lay at a much lower level than it does to-day, 

 and the ice mantle of Mount Rainier expanded not 

 merely by the forward lengthening of its ice tongues but 

 by the birth of numerous new glaciers about the moun- 

 tain's foot. The large size of the empty cirques and 

 canyons, moreover, leads one to infer that many of 

 these new glaciers far exceeded in volume the ice 

 streams descending the volcano's sides. The latter, it 

 is true, increased considerably in thickness during 

 glacial times, but not in proportion to the growth 

 of the low-level glaciers. Nor is this surprising in 

 view of the heavy snow falls occurring on the moun- 

 tain's lower slopes. There is good reason to believe, 

 moreover, that the cool glacial climate resulted in a 

 general lowering of the zone of heaviest snowfall. It 



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