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GEOLOGY OF EASTERN WISCONSIN. 



the adaptabilities of this class, or measure its fertility. Some por- 

 tions, with simple drainage, will produce the most luxuriant growth 

 of grass or grain. Others are impregnated with organic acids derived 

 from the humus, and are known as " sour soils," and are unfit for the 

 growth of the cereals and the better class of grasses. Others still are 

 so largely composed of organic matter that they do not contain the 

 requisite amount of mineral ingredients. The character of the vege- 

 tation naturally growing upon it is the best indication of the nature 

 of any given example of this class. 



Alluvial Soils. Closely associated with this last class, and inter- 

 mediate between it and the prairie loam, we find a soil formed by the 

 accumulation of sediment washed from the uplands and deposited on 

 the bottom lands adjacent to streams, and in other favorable localities. 

 It is better marked in its origin than in its character, for when min- 

 eral ingredients predominate, it very closely resembles the prairie 

 loam, both in the fineness of the material and in its chemical nature, 

 and when vegetable matter becomes predominant it does not differ 

 essentially from the humus soils. For this reason, and because its 

 distribution has no special significance in studying agricultural prob- 

 lems, it has not been mapped as a separate class, although it occupies 

 in the aggregate a large area, and is an exceedingly fertile and valu- 

 able soil. The following analyses are by Mr. Bode: 



