BLUE EARTH COUNTS. 441 



Glacial drift,] 



cases this soft and moist deposit is evidently stratified clay, free from gravel 

 or only holding here and there a stone, and all varieties appear to be found 

 between this and an unstratified and very pebbly till; as indeed it may be 

 that the latter in different localities shows all gradations from its occasion- 

 ally very soft character, where a shovel can be easily thrust into it to the 

 depth of a foot or more, to the hardest deposits of the lower till in which 

 a pick can be driven only an inch or two at one blow. 



The few beds found in this district which contain shells or trees that 

 nourished in interglacial epochs, lie beneath two distinct beds of till, the 

 lower sometimes showing its usual hard and compact character, but else- 

 where being even softer than the upper till. 



Excepting the division into beds as before described, the till is an en- 

 tirely unstratified deposit. There has been no assortment of its materials 

 by water, and the coarsest and finest are mingled confusedly in the same 

 mass. Often a thickness of fifty feet or more exhibits no evidence of 

 stratification. 



The motion of the ice-sheet upon this part of the state was from north- 

 west to southeast, as is shown by the direction in which the boulders of the 

 drift in this region have been carried, and by the courses of the glacial 

 striae, or the scratches and grooves worn on the surface of the bed-rock by 

 stones and boulders carried along in the ice. Small rock fragments, vary- 

 ing in size up to the dimension of six inches, are usually numerous and 

 scattered through all parts of the till; they are, however, seldom abundant, 

 and are sometimes so few that in well-boring none might be encountered. 

 Boulders of large size are less frequent, and often a well or even a railroad 

 cut in till fails to display any of greater dimension than two or three feet. 

 Again, several may be found ot various sizes up to five or perhaps seven or 

 eight feet. They appear to be usually more numerous on the surface of 

 the till than below. The number of boulders over one foot in size to be 

 found generally upon the surface of moderately undulating tracts of till is 

 estimated to vary from one or two to ten on an acre; but often, and espec- 

 ially on smooth or flat areas, they are more scarce, so that perhaps a dozen 

 could not be gathered on a square mile. 



The very smooth, and in many portions flat, surface of the southern 

 two-thirds of Blue Earth county, and of the township of Mankato east from 



