58 



THE ICE AGE IN NORTH AMERICA. 



nate. Eventually this stream will break out in the rear of 

 that deposit also, and leave another ridge similar to the one 



Fig. 26.— In the foreground on the right is a mass of ice, one half mile in front of the gla- 

 cier, one hundred or more feet thick, covered with gravel, slowly sliding down to form 

 the rim of a kettle-hole. The mountain back is 3,100 feet high. Near B, Fig. 22. 



now slowly settling down into position south of it. This first 

 ridge south of the subglacial stream, with its ice still melting 

 in exposed positions under its covering of gravel, can not be 

 many years old. 



Still another sign of the recent date of this whole moraine 

 appears at various places where water-courses, coming down 

 from the mountain, are depositing superficial deltas of debris 

 upon the edge of the glacial deposit. These deltas are very 

 limited in extent, though the annual deposition is by no 

 means insignificant. At the southern apex of the moraine, 

 three miles below the ice-front, and but one hundred or two 

 hundred yards from our camp, great quantities of debris came 

 tearing down in repeated avalanches during a prolonged sea- 

 son of rain. Twenty-five years would be more than ample 

 for the formation of the cone of debris at the foot of this line 

 of avalanches. Thus there can be no reasonable doubt that 



