606 



THE ICE AGE IN NORTH AMERICA. 



" Along both the Atrevida and the Malaspina glacier mar- 

 gins, the glacier and glacial deposits are advancing in forested 

 regions and overspreading old soils, peat beds, and forests. 

 When the process of present change is at an end there will 

 be in this region soil beds and plant beds inter bedded with 

 glacial deposits, and all as the result of a sudden change in 

 glacier-margin conditions. It requires no elaboration of this 

 subject to make it clear that here is a hint of great significance 

 in the interpretation of pleistocene deposits. In view of 

 such phenomena as those described above it is evident that the 

 interpretation sometimes placed upon plant beds and soil beds 

 intercalated in pleistocene deposits — namely, that they prove 



Fig. 154 — Forest lately disturbed and about to be overwhelmed by an advancing Alaskan 

 glacier. (Photo by Gilbert. ) 



separate glacial epochs — can hardly stand without the support 

 of other and convincing evidence that the plant or soil bed 

 interval was of long duration."* 



All this is in the region where the natural drainage is to the 

 south ; but, upon entering the northern water-shed, especially 

 in the area now covered by the deposits of Lake Agassiz, in- 

 terglacial deposits would seem necessarily to imply that the 



* R. S. Tarr and B. S. Butler, "The Yakutat Bay Region, Alaska," 

 "U. S. Geological Survey," "Professional Paper," 64, pp. 86, 87. 



