474 



GEOLOGY. 



snow banks at the bases of the mountains. The descending talus 

 rolls out over the snow, lodging at its outer edge. ]( is possible that 

 in some of these cases there is incipient slumping of the talus itself. 

 Fig. 556 shows another type of talus accumulation common in some 

 of the higher mountains of the west. In some cases these bodies of 

 talus have the general outline of a glacier, and have therefore been 

 called " talus glaciers." Their development probably involves several 





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Fig. 55G. — An accumulation of talus, where slumping, etc., have been operative. 

 Near Silverton, Colo., at head of Horseshoe basin. (Cross, U. S. Geol. Surv.) 



processes besides the descent of loose material down steep slopes. 

 These processes probably include (1) the passage of the talus over 

 snow-banks at the bases of cliffs, (2) sliding, creeping, and slumping 

 of bodies of talus, perhaps both when bound together by ice and 

 when not so cemented, and (3) incipient glacial motion. 



All such accumulations now conspicuous in the western mountains are 

 largely or wholly post-glacial, and their development is still in progress. 



Eolian deposits. — One of the agencies concerned, both with erosion 

 and deposition, in the western region, is the wind. Its erosive work 

 is shown in the peculiar carving which affects the cliffs and projec- 



