11 



A long period of time, includiiiij several epochs of glaciation as well 

 as long interglacial periods, in which floras and faunas were devel- 

 oped, elapsed between the two. lioth glaciers radiated from Keewatin 

 centers and accordingly brought along with them similar material, the 

 chief characteristic of which was an abundance of limestone fragments. 

 Thus we have in Rice county, side by side, the soils developed on 

 the oldest exposed and those on the very youngest of the glacial forma- 

 tions, both, since the melting of the last ice-sheet, subjected to the 

 same climatic influences and ex])osed to the same soil forming agencies. 



For such a study it is highly desirable to be able to compare soils 

 formed luider dififerent vegetation conditions, e. g., forest soils on the 

 earlier drift with forest soils on the later, the natural grassland soils 

 on the former with natural grassland soils on the latter. Rice is the 

 only county in which this is possible, the other counties in which the 

 tw'o selected drifts occur side by side being south of the limit of the 

 forest (Fig. 2). 



Further, for Rice county there was available a detailed soil sur- 

 vey by the United States Bureau of Soils made in 1 WJ and i)ublished in 

 1911 (11) while Leverett, who was completing a detailed study of the 

 glacial history of the state, kindly made a detailed demarcation 

 of the eastern boundary of the Late Wisconsin glaciation within the 

 county, this having not yet been reported in printed form. 



In the survey by the Bureau of Soils the two drifts exposed on 

 the surface are mentioned (11, p. 21-23), Leverett having personallv 

 indicated the boundaries to the surveyors but no attempt was made by 

 the latter to difTerentiate types in respect to the two drifts although it is 

 stated (11, p. 21) that "the limestone from which much of this drift 

 (Kansan) is derived, has long since given way to the agencies of 

 weathering and only the more resistant rocks are left, whereas in the 

 Wisconsin drift limestone and shales in addition to numerous cherty 

 and crystalline rocks are very common." Fourteen types of soil were 

 mapped, of which three of the most extensive, viz., Carrington silt 

 loam, Fargo silt loam, and Carrington loam, have representative areas 

 on both drifts. 



Thus Rice Count}- offered an exceptional op]Jortunity not only for 

 the study of the differences in the mechanical, chemical and petrograh- 

 ical composition resulting from the difference in age of the drift and 

 the consequent longer-continued leaching on the one than on the other, 

 but also to determine whether soil classification as applied by the United 

 States Bureau of Soils properl)' recognizes differences between soils on 

 different drifts. 



Soil Types Studied. 

 Only four soil types are dealt with in the present study, viz.. 

 Carrington silt loam, Fargo silt loam. Carrington loam and ^Marshall 

 silt loam. A soil type, as the term is employed by the U. S. Bureau of 

 Soils (12, p. 11), is the unit of classification and is defined as including 

 all soils that are alike agriculturally, or as nearly alike as it is possible 

 to detemiine bv field methods. 



