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TH E ATMOSPHERE — FROST 



causes the fragments to rise slightly at right angles to the inclined 

 surface, and each thawing produces a reverse movement ; hence 

 the slow creep down the slope. 



The action of frost is, of course, practically absent in the low- 

 lands of the tropics, but in high mountains and in all countries 



Fig. 26. — Shales " creeping" under the action of frost. (U. S. G. S.) 



which have cold winters, frost is an agent of great importance in 

 the mechanical shattering of rocks and slow destruction of cliffs. 

 The hardest rocks are shivered into fragments and, dislodged from 

 their places, the fragments roll down the mountain side till they 

 come to rest, perhaps thousands of feet below. Immense accumu- 

 lations of frost- made talus are to be found in such places as the 

 foot of the Palisades of the Hudson, the abrupt southern slope of 



