10 



Rice, Dodge, Olmstead, Goodhue, Mower. Fillmore, Pipestone and 

 Rock counties. Its presence in the last two counties named was not 

 recognized by glacial geologists until after the field work in this study 

 had been completed. 



The Illinoian, the third to reach the state, covered only a small area 

 in Washington count}- and the greater part of Dakota county. It came 

 from a Labradorian center and over-rode the Kansan. The till left be- 

 hind is designated the Old Red Drift. 



The fourth advance of the ice into Minnesota, the Early Wiscon- 

 sin, approached from the northeast and covered a considerable area 

 to the west and southwest of Lake Superior (Fig. 1) and left a mantle 

 of till known as the Young Red Drift. These two ice sheets crossing 

 highly ferruginous rock formations gathered up portions of these and, 

 consequently, the soils developed upon the till show a distinctly red 

 color. 



The fifth ice sheet, the Late Wisconsin, which brought the Late 

 Gray Drift, radiated from a Keewatin center to the north or slightly to 

 the northwest of Minnesota and covered a much larger portion of the 

 state (Fig. 1) than either of its immediate predecessors. This younger 

 formation in contrast to the Old Gray Drift is characterized by numer- 

 ous lakes and poorly drained areas such as the deposits older than the 

 Young Red Drift do not possess. Fully developed drainage lines are 

 to be found only where they were formed by the out-rushing water 

 from the melting ice. 



In addition to the Des Moines Lobe of the Late Wisconsin there 

 was a contemporaneous Superior Lobe in which the ice advancing 

 up to the bed of Lake Superior spread to the north, northeast, east 

 and southeast. The till, almost free of limestone, was derived from 

 crystalline rocks and, like the Illinoian and early Wisconsin in Min- 

 nesota, has a red color. 



Each period of glaciation was separated from the succeeding one 

 by an interglacial interval which, in some cases, was very long, prob- 

 ably much longer than the time which has elapsed since the Late 

 Wisconsin. The successive stages appear to have become shorter, the 

 earlier being much longer than the later ones (13, p. 382). 



Advantages Offered by Area Selected. 



Rice county in southeastern Minnesota ottered the best site in 

 the State for a study of the influence of the age of a glaciation upon 

 the character of the soils. The earliest glaciation from which any 

 till remains uncovered by later deposits, the Kansan, covered the whole 

 of what is now included in the county boundaries while the most recent 

 of all the glaciations. the Late Wisconsin, covered only the western 

 two-thirds and no intenening ice sheets had entered the area, except 

 possibly the Earh Wisconsin at the very edge on the north (Fig. 1) 



