MODIFIED DRIFT EXTENDING SOUTHEAST WAED 429 



Drift limestone is absent or very rare on the east, because no limestone 

 formations were crossed within, several hundred miles by that part of the 

 ice-sheet ; but on the west the drift, consisting chiefly of a thick sheet of 

 till, contains much fine limestone detritus, sand and gravel, and frequent 

 boulders of limestone, borne southeastward from Manitoba over the 

 Archean area of the southwest part of the Lake of the Woods, of Eainy 

 River, and of northern and central Minnesota. In the same directions 

 with the slopes of the ice surface, which are known from the courses of 

 the glacial striae ,and the transportation of the drift, the streams of the 

 glacial melting flowed convergently from the east and west, from the ice 

 over northern Minnesota and eastern Manitoba on one side, and from that 

 over the Red Eiver valley and western Manitoba on the other, toward 

 this belt of plentiful superficial deposits of gravel and sand. 



Evidence of much englacial and superglacial Drift 



The chief reason for the detailed descriptions presented in the fore- 

 going pages is my wish to have other field workers and theorists in gla- 

 cial geology come to my point of view and conclusions, that a great 

 amount of drift was contained in the lower part of the ice-sheet, was 

 carried along with its motion, and during the final melting became super- 

 glacial when the upper part of the ice melted away. The esker deposit 

 of Birds Hill is shown by the wells in and near it to extend 50 or 60 

 feet below the general level of the Eed Eiver Valley plain, to a depth 

 only 10 feet above the limestone bedrock. Seeing that the esker gravel 

 and sand were originally deposited, as before shown, at or above the level 

 of Lake Agassiz, which in its earliest and highest stage here, at the time 

 of this esker river, was 500 feet above the land surface, I must conclude 

 that the englacial and later superglacial drift of the ice-sheet here above 

 that level amounted to about 20 feet, the thickness of the till above the 

 coarse gravel in Mr. McGregor's well. 



Beneath the level of the glacial lake, in the lower 500 feet of the ice- 

 sheet, the quantity of englacial drift seems to have given a thickness of 

 10 feet, if we thus consider the entire drift deposit beneath the coarse 

 gravel in this well, attributing none of it to subglacial deposition. 



As the surface at the well is 6 or 8 feet above the general level of the 

 adjoining valley plain, its depth of 70 feet to the bedrock indicates that 

 the general sheet of the drift and lacustrine and alluvial beds together 

 averages 60 feet in thickness in this vicinity. From my observations of 

 till at or near the surface of the valley plain in many tracts about Birds 

 Hill and Winnipeg, and elsewhere along all the length of the Eed Eiver 



