668 THE ICE AGE IN NORTH AMERICA. 



of considerable importance as well as interest. Many have 

 seemed to assume that they could come into position only 

 by being dropped into the water from a boat. The accompany- 

 ing illustration, however, from a photograph of Professor 

 Russell taken in front of the Malaspina Glacier, Alaska, 

 shows what was doubtless the real method. A glacial delta 

 is here seen in process of formation. In the summer time, 

 when the drainage channels were overcharged both with 

 water and debris they would build up a delta terrace near 

 their mouth. During a considerable portion of the year, 

 however, these deposits would be exposed surfaces over 

 which rna^n could wander and hunt at his leisure. In the 

 illustration such a stream has been diverted into a forest and 

 is fast burying the trees, as is seen to have been the case in 

 front of the Muir Glacier (seefrontis plate). At Trenton, 

 Newj Jersey, this exposed delta terrace would have been 

 doubly attractive to man from the fact that it contained 

 many pebbles of argillite from which he was accustomed to 

 manufacture his implements. 



