ENGLACIAL AND SUPERGLACIAL DRIFT IN MINNESOTA, THE 

 DAKOTAS, AND MANITOBA. 



By Warren Upham, D. Sc, St. Paul, Minn. 



[Abstract of a paper read before the Minnesota Academy of 

 Sciences, December 7, 1909.] 



Modified drift, consisting of stratified gravel and sand, with local 

 deposits of clay, overlies the bed-rocks and the till, and generally forms 

 the surface, on an extensive area stretching from St. Paul and Min- 

 neapolis northwestward to the lakes at the sources of the Mississippi, 

 and onward to the Rainy river, the southwest side of the Lake of the 

 Woods, and to the vicinity of the city of Winnipeg. The contour of 

 the greater part of these deposits, through their extent of 400 miles, is 

 fiat or moderately undulating, and their surface varies in height from 

 a few feet to 50 feet or rarely more above the adjoining lakes and 

 streams. In central Minnesota these tracts of gravel and sand have 

 an elevation that increases from south to north, being 825 to 950 feet 

 above sea level near the Twin Cities, rising gradually to 1,200 feet in 

 the distance of about 100 miles northwest to Brainerd, and ranging 

 from 1,350 to 1,500 feet between the Leaf hills and Itasca lake. 

 Thence their surface sinks to 1,150 to 1,075 feet in the vicinity of 

 Rainy river and the Lake of the Woods, and is between 750 and 875 

 feet in the district close northeast of Winnipeg, where a part of these 

 deposits forms a remarkable esker, named Bird's Hill. 



On each side this broad belt is bordered by areas of nearly the 

 same general elevation, which have mostly a surface of till; and it 

 is to be remarked that the heights of the tracts of modified drift and 

 till are alike determined by that of the underlying rocks, on which 

 these superficial deposits are spread in a sheet of slight depth in 

 comparison with the gradual change in their elevation. The drift 

 sheet on this belt, including both the sand and gravel and the till, 

 probably varies in its average thickness from 50 to 150 feet, while its 

 central portion rises 400 to 600 feet above its south and north ends. 



The distribution of the modified drift thus found upon large 

 tracts along a wide belt from St. Paul to Winnipeg, while it is more 

 scantily developed on a still wider region of Minnesota, South and 

 North Dakota, and Manitoba, southwest of this belt, and likewise is 

 scanty or wanting on its northeast side in northern Minnesota and 

 about Rainy lake and the northeast and north portions of the Lake of 

 the Woods, seems to be attributable to converging slopes of the sur- 

 face of the ice-sheet and the consequent convergence of its currents, 

 which brought an unusual amount of englacial drift into the ice along 

 this belt, and by which also the streams produced in its melting were 

 caused to fiow thither from extensive tracts of the ice on the east and 

 west. The glacial striae of these adjoining areas show that on the 

 east the course of the motion and the descent of the surface of the ice- 

 sheet were from northeast to southwest, but that on the west the 



