1887.] 443 [Upham. 



ocean. Along the Mississippi the flood-plain of modified drift at 

 Brainerd has a height of about 60 feet above the river ; at Little 

 Falls, as before noted, its height is 25 to 30 feet ; at Saint Cloud, 

 60 feet ; at Clearwater and Monticello, 70 to 80 feet ; at Dayton, 

 45 feet ; and at Minneapolis, 25 to 30 feet above the river at the 

 head of Saint Anthony's Falls. 



The modified drift at Little Falls lies on the till or direct deposit 

 of the ice-sheet, and forms a surface over which the ice never re- 

 advanced. It lies far within the area that was ice-covered in the 

 second and latest principal epoch of glaciation, and by reviewing 

 the steps in the recession of the ice of that epoch we shall be able 

 to ascertain approximately what were the outlines of its receding 

 margin when the gravel and sand plain of Little Falls was depos- 

 ited, enclosing these evidences of man's presence. The ice-sheet, 

 supplying both this modified drift and the floods by which it was 

 brought, still covered much of the upper part of the Mississippi 

 basin, which only reaches about a hundred miles north of Little 

 Falls ; and the courses of massive morainic belts show the contin- 

 uation of the glacial boundary northwestward across Dakota and 

 with less clearness eastward across the Laurentian lakes. 



When the latest North American ice-sheet attained its greatest 

 area, its southern portion from lake Erie to Dakota consisted of 

 vast lobes, one of which reached from central and western Minne- 

 sota south to central Iowa. This lobe in its maximum extent 

 ended near Des Moines, and its margin was marked by the Alta- 

 mont moraine, the first and outermost in the series of eleven dis- 

 tinct marginal moraines of this epoch which are recognizable in 

 Minnesota. When the second or Gary moraine was formed, it ter- 

 minated on the south at Mineral ridge in Boone county, Iowa. 

 At the time of the third or Antelope moraine, it had farther re- 

 treated to Forest City and Pilot mound in Hancock county, Iowa. 

 The fourth or Kiester moraine was formed when the southern ex- 

 tremity of the ice-lobe had retreated across the south line of Min- 

 nesota and halted a few miles from it in Freeborn and Faribault 

 counties. The fifth or Elysian moraine, crossing southern Le 

 Sueur county, Minnesota, marks the next halting-place of the ice. 

 At the time of formation of the fifth moraine, the south end of the 

 ice-lobe had been melted back a hundred and eighty miles from its 

 farthest extent, and its southwest side, which at first rested on the 

 crest of the Coteau des Prairies, had retired thirty to fifty miles 



