144 



PHYSICAL GEOLOGY 



Fig. 126. — Cirques or feeding ground, and medial moraine 

 of the Breithorn Glacier. (Photo. L. E. Westgate.) 



slowly down the mountain valley until it reaches a point where the 

 melting equals the forward movement (p. 159), the size of the glacier 



depending (1) upon 

 the area of the neve 

 field drained by it, 

 (2) upon the amount 

 of the precipitation, 

 and (3) upon the rate 

 of melting. Some- 

 times glaciers flow 

 between forests and 

 even cultivated fields, 

 as, for example, in the 

 valleys of Grindel- 

 wald and Chamonix, 

 where glaciers lie 

 within a few hundred 

 feet of the homes of 

 the inhabitants. In New Zealand a glacier from the Mt. Cook range 

 discharges its debris in the midst of subtropical vegetation. 



Cirques. — One of the most striking and beautiful features of the 

 Alps in Switzerland, 

 of the Selkirks • in 

 Canada, of the Rocky 

 Mountains of the 

 United States, and of 

 other high mountains 

 of the temperate re- 

 gions are the ragged 

 crests (Fig. 127) sepa- 

 rating the gigantic 

 semicircular cirques, 

 which hang high up 

 on the mountain sides. 

 These cirques domi- 

 nate the high moun- 

 tains and correspond 

 to the limit of per- 



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127. 



Cirques and small glacier, St. Christophe, 

 France. 



petual snow of the Glacial Period (p. 141). Their walls are rough 

 and precipitous, while their floors are comparatively smooth and 



