PHYSICAL AND CLIMATAL CONDITIONS. 97 



" These conditions insure such accumulations of snow 

 above the line of perpetual frost as will sooner or later 

 descend below the line of perpetual snow and .be changed 

 to ice and water. 



" The water forms glacial rivers, and the ice will move 

 as a plastic mass to a line determined by the amount of 

 snow on the one hand and the climate on the other. 



" The advancing movement of the glacier is accompanied 

 by erosion and scratching of the rocks below and by the 

 formation of different kinds of moraines, as till or blue 

 boulder-clay, and yellow unstratified masses — terminal, 

 lateral and superficial moraines. Simultaneous with these 

 phenomena, we have the action of the glacial rivers, 

 consisting in a partial denudation of the moraines, and 

 the formation of stratified gravel, sand and clay." 



He next explains his own views of the glaciation and 

 dispersion of erratics from Scandinavia as a centre by the 

 movement of glaciers, and applies these to America, 

 admitting, however; that here there must have been 

 separate centres of dispersion in the east and west. He 

 thus states the objections to the current views of American 

 land-glacialists : 



" It has been the opinion of many distinguished Ameri- 

 can geologists that the source of the eastern ice-field is to 

 be searched for in tlie Canadian highland. Against this 

 opinion several important reasons may be urged. First, 

 in those parts of Canada in which the glaciers in question 

 are supposed to have originated, we have reason to 

 believe that the rocks are rounded and scratched, pheno- 

 mena everywhere recognized as glacial, but, I think, in no 

 case characterizing rocks known to have been covered 

 with perpetual snow. 



