I'HY.SICAL AND CLIMATAL CONDITIONS. 97 



"Tliese coiulitioiis insure sucli iiccumulatious of snow 

 above tlie line of perpetual frost as will sooner or later 

 descend l)elow the line of perpetual snow and be changed 

 to ice and water. 



" The water forms ,i;lacial rivers, and the ice will move 

 as a plastic mass to a line determined l)y the amount of 

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



" The advanciuL!," movement of the glacier is accompanied 

 by erosion and scratching of the rocks below and by the 

 formation of dif'l'erent kinds of moraines, as till or blue 

 1)oulder-clay, and yellow unstratified masses — terminal, 

 lateral and superficial moraines. Simultaneous with these 

 phenomena, we have tlie action of tlie 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 glaciatiou 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 

 tlius states the objections to the current views of American 

 land-glacialists : 



" It lias been the opinion of m my distinguished Ameri- 

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

 be searched for in the Canadian highland. Against this 

 opinion several important reasons may be urged. First. 

 in those parts of Canada in wliicli the glaciers in question 

 are sup])osed 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 

 witli perpetual snow. 

 8 



