STRATIFIED DRIFT 959 



])onds were continually being drained, as their outlets, hitherto 

 choked bv the ice, were opened, while others were coming into 

 existence as the depressions in the surface just freed from ice, 

 filled with water. Lacustrine deposits at the edge of the ice 

 during its retreat were in all essential respects identical with 

 those made in similar situations during its maximum extension. 

 Disregarding oscillations of the ice edge at these stages, the 

 deposits made by extraglacial waters during the maximum 

 extension of an ice-sheet, and during its retreat, were always 

 left at the surface, so far as the work of that ice-sheet was con- 

 cerned. The stratified drift laid down by extraglacial waters in 

 these stages of the last ice-sheet which affected any region of 

 our continent still remain at the surface in much the condition 

 in which they were deposited, except for the erosion they have 

 since suffered. It is because of their position at the surface 

 that the deposits referable to these stages of the last ice-sheet 

 of any given region have received most attention and are there- 

 fore most familiar. 



DEPOSITS MADE BY EXTRAGLACIAL WATERS DURING THE ADVANCE 



OF THE ICE. 



During the advance of an ice-sheet, if its edge forged 

 steadily forward, the waters issuing from it, and flowing beyond, 

 were effecting similar results. They were starting valley trains, 

 overwash plains, kames, and small ill-defined patches of strati- 

 fied drift which the ice did not allow them to complete, 

 before pushing over them, and shoving forward the zone of 

 activity of extraglacial waters. Unlike the deposits made by 

 the waters of the retreating ice, those made by the waters of the 

 advancing ice were laid down on territory which had not been 

 glaciated, or at least not by the ice-sheet concerned in their 

 deposition. If the ice halted in its advance, there was at such 

 time and place opportunity for the better development of extra- 

 glacial stratified drift. 



Lakes as well as streams were concerned in the making of 

 stratified beds of drift, during the advance of the ice. Mar- 



