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A glacier may move forward only a few feet 

 in a year or it may move several feet in a day. 

 It may be only a few hundred feet in length, or, 

 as during the Ice Age, have an area of thousands 

 of square miles. The Arapahoe Glacier moves 

 slowly, as do all small glaciers and some large 

 ones. One year's measured movement was 27.7 

 feet near the centre and 11.15 near the edge. 

 This, too, is about the average for one year, and 

 also an approximate movement for most small 

 mountain glaciers. The centre of the glacier, 

 meeting less resistance than the edges, com- 

 monly flows much more rapidly. The enormous 

 Alaskan glaciers have a much more rapid flow, 

 many moving forward five or more feet a 

 day. 



A glacier is the greatest of eroding agents. It 

 wears away the surface over which it flows. It 

 grinds mountains to dust, transports soil and 

 boulders, scoops out lake-basins, gives flowing 

 lines to landscapes. Beyond comprehension we 

 are indebted to them for scenery and soil. 



Glaciers, or ice rivers, make vast changes. 

 Those in the Rocky Mountains overthrew cliffs, 



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