Uphara.] 438 [Dec. 21, 



shown. The recession of the ice-sheet of the last glacial epoch 

 in Minnesota, to which this will direct our attention, seems to be 

 clearly marked by as many as ten stages of halt or re-advance, in 

 which distinct marginal moraines were accumulated, besides the 

 moraine on the limits of its farthest extent. Six summers of geo- 

 logic field-work in that state have been spent by the writer chiefly 

 in the examination of its glacial and modified drift, of these mo- 

 raines, and of the beaches and deltas of the glacial lake Agas- 

 siz, which was formed in the valley of the Red river of the north 

 and of lake Winnipeg by the barrier of the departing ice-sheet. 

 In their bearings upon this subject, my observation and study of 

 that region convince me that the rude implements and fragments 

 of quartz discovered at Little Falls were overspread by the glacial 

 flood-plain of the Mississippi river, while most of the northern half 

 of Minnesota was still covered by the ice, contemporaneously with 

 its formation of the massive moraines of the Leaf hills and with 

 the expansion of lake Agassiz on their west side, respectively 60 

 and 85 miles west of Little Falls. This was during the highest 

 stage of lake Agassiz, and previous to its extension beyond the 

 north line of Minnesota and Dakota. More than twenty lower 

 beaches of this glacial lake have been traced, belonging to later 

 stages in the recession of the ice-sheet, before it was melted so 

 far as to reduce lake Agassiz to its present representative, lake 

 Winnipeg. Estimated by comparison with the series of moraines 

 and beaches formed during the glacial recession, the date of the 

 gravel plain at Little Falls appears to be about midway between 

 the time of maximum extent of the last ice-sheet and the time of 

 its melting on the district across which the Nelson river flows to 

 Hudson bay. 



The town of Little Falls is on the east bank of the Mississippi 

 river, in Morrison county, near the geographic centre of Minne- 

 sota. It is about a hundred miles northwest from Saint Paul and 

 Minneapolis, and nearly an equal distance southeast from Itasca 

 lake. The elevation of Itasca lake is about 1450 feet above the 

 sea ; of the Mississippi, at the head of the rapids, or Little Falls, 

 from which the town derives its name, 1090 feet ; and at the head 

 of Saint Anthony's Falls in Minneapolis, 796 feet. Following the 

 general course of the river, without regarding its minor bends, its 

 descent from lake Itasca by Little Falls to Minneapolis averages 

 about two feet per mile, and is approximately uniform along the 



