The Ice-currents of Minw^mtii f'p/tani. r>o 



The cau.se of tliis cliaji«4ed euiirse of the line at which the cur- 

 rents of the west and east portions of the ice-sheet met, is to be 

 found in the changed meteorological conditions of this time. Dur- 

 ing the increased ice-melting attendant upon the recession of the 

 ice-fields from the outer to the inner terminal moraine, the pre- 

 vailing westerly winds sweeping over the western side of the ice- 

 sheet upon the Coteau des Prairies and eastward became more 

 laden with moisture than in the earlier part of this epoch, wlien 

 there was com])aratively little melting upon the surface of the ice: 

 and the increased temperature enabled these winds to carry their 

 moisture farther than when the ice had its greatest extent. Then 

 the precipitation of rain and snow took place more upon the west- 

 ern side of the ice; but at this later time the precipitation, by 

 reason of the causes here mentioned, probably became much 

 greater than before upon the east part of the lobe of the ice-sheet 

 that extended southeastward from I he Red river valley to central 

 Iowa. Before this, lake Minnetonka and central Wright county 

 had been the limit where this ice-flow was stopped by the opposing 

 ice-current from lake Superior: but now, because of the relatively, 

 and perhaps absolutely, greater thickness of this part of the ice 

 flowing from the northwest, due, as shown, to climatic changes, 

 its current pushed back that opposed to it on the east, covering 

 the red till brought by that ice with blue till containing plentiful 

 limestone boulders and other material from the west and north- 

 v/est. The limit whei-e these ice-fields, moving from the west and 

 from the northeast, now met, lies in the south edge of Mille L-ics, 

 Kanabec, and Pine counties, and even beyond the St. Croix river 

 at the east side of Chisago county, fully seventy-five miles east of 

 the line where these ice-currents formerly met; but it scarcely 

 reaches into Washington and Uamsey counties, which remained 

 covered with ice that came from the northeast. This persistence 

 of the ice-rtow from the northeast near the margin of the ice- 

 covered area, and also in Stearns and Morrison counties north of 

 the changed portion of the line of confiuence of these ice-fields, 

 ])roved by the character of the drift upon these counties, seems 

 yet quite consistent with this explanation, by meteorological 

 causes, of the change in source of the ice covering the intervening 

 district, from Wright and Hennepin counties eastward to ihe, St. 

 ^'roix river and the edge of Wisconsin. 



Details of sections in the drift, shoAving the blue (or next to 



