ESlCERS IN DAKOl^A AND MANITOBA. 77 



mound I think to have been deposited where a glacial river descended 

 from the convergent slopes of the ice-sheet to the open land contem- 

 poraneously with the formation of the Dovre moraine. Its material 

 therefore is regarded as englacial drift which had become superglacial. 



It seems very difficult or impossible to entertain the alternative hy- 

 pothesis, that the stream bringing this gravel and sand and heaping it 

 in this high, lonely hill, 175 feet above the surrounding country, came 

 from a subglacial tunnel which would pass across the bed of the lake a 

 few miles distant on the north and more than 300 feet below the hill 

 crest. Could a stream flowing upward from beneath the ice form a lone, 

 conical mound of so great height and carry bowlders up to its summit? 



Bird's Hill, an Esker near Winnipeg, Manitoba. 



Seven miles northeast of Winnipeg, at the station of Bird's Hill on the 

 Canadian Pacific railway, is the esker from which the station was named. 

 This massive ridge of gravel and sand extends about one and a half miles 

 in an east-southeast course and has a height about 50 feet above the very 

 flat expanse of the vast plain of the Red 'River valley which stretches far 

 away to the west, its altitude here being represented by the railwa}^, 759 

 feet above the sea. On the northern slope of the esker are strewn rather 

 plentiful bowlders, but none or very few occur on its top and southern 

 slope, and none are imbedded in its mass, which is well revealed by an 

 extensive excavation for railway ballast. This hill, which I have more 

 fully described elsewhere,'=^ seems to me clearl}^ referable to deposition 

 by a river flowing down from the surface of the melting ice-sheet on the 

 north. The bowlders were doubtless dropped or stranded from bergs 

 and floes on the surface of the glacial lake Agassiz, before the border of 

 the ice-sheet had retreated from the vicinity. Indeed, their occurrence 

 chiefly on the northern slope indicates that thej^ were mostly stranded 

 there while ice yet remained beneath this deposit and prevented its 

 entire submergence in the lake. The thickness of underlying ice, when 

 it permitted the bowlders to l)e stranded only on the northern side of 

 the ridge, must have slightly exceeded 500 feet, since that was the depth 

 of the early highest stage of the ice-dammed lake above the top of Bird's 

 hill. We thus learn that much drift had been enclosed within the ice- 

 sheet at greater altitudes than 500 feet above the very level country on 

 which it rested and from which the drift had been eroded and borne 

 upward into the ice. 



Another very noteworthy observation suggests that the volume of the 

 englacial and finally superglacial drift above that height averaged several 



*Geol. and Nat. Hist. Survey of Canada, Annual Report, new series, vol. iv, for 1888-'89, pp. 38-42E. 



