GROUND-ICE WEDGES 



643 



than ten feet high and the bottom is nearly always concealed by 

 slumping. The maximum vertical dimension observed is about 3 

 meters, but the wedge had a thickness sufficient to have carried it 

 two or three times as far down before pinching out. The ultimate 



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III 1,1 »«•'"; 1 1 'o 



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Fig. 9. — A narrow ice wedge in a deposit of mixed clay and ice grantdes. An 

 open crack within the wedge. 



Gro^JL^a. Ite 



Fig. id. — ^A narrow ice wedge in muck beds; an open frost crack runs through 

 the turf and into the ice. 



depth must depend upon the depth of annual change in ground 

 temperature in the region. The constants are so uncertain that 

 it is impossible to make a close calculation of this depth. For the 

 purposes of this paper the depth of the ice wedges is assumed to be 

 from 8 to 10 meters. 



