84 TRANSACTIONS OF THE ILLINOIS 



more at length will find them set forth in detail in the chapter on the 

 " Origin and Formation of the Prairies," in the first volume of the Geo- 

 logical Survey of this State. The theory above set forth is a very plausible 

 one to account for the formation of the peculiar soil and subsoil of the 

 prairies of this and some of the adjoining States, whatever may be our 

 views as to its application to more extended areas, or upon the question 

 whether its peculiar character and composition afford a satisfactory expla- 

 nation of the absence of forest trees upon its surface. At any rate, it 

 shows us how a soil may have been formed upon the surface it now occu- 

 pies, by the growth and decomposition of aquatic plants, and hence form 

 an exception to the general rule already given as to the origin of soils. 

 But the prairie soil, whatever its origin, is one of the most productive in 

 the West, and is rich in the essential elements required for the production 

 of all the cereals, grasses, vegetables and fruits adapted to a temperate 

 climate ; and in its productive capacity it is not surpassed by any other 

 variety of soil of equal extent upon this continent. 



Whatever may have been the cause of the absence of an original 

 forest growth upon the prairies, the fact has been clearly demonstrated 

 that, when this soil has been once broken up, and the soil and subsoil 

 mingled together with the plow, it becomes adapted to the growth of for- 

 ests, as well as fruit trees, and the prairie farmer may surround his home- 

 stead Avith a luxurious growth of such forest trees as his interest or fancy 

 may prompt him to plant. 



When we leave the level of the high prairie, and descend but a few 

 feet along the slopes leading to valleys of the streams, we find a decided 

 change taking place in the color and composition of the soil, and by turn- 

 ing up the subsoil we shall find that composed of the gravelly clays of 

 the drift. This is a true drift soil, and to it we are indebted for most of 

 the upland forests throughout the prairie region. This soil is usually of 

 an ash gray, or chocolate brown color, varying according to the char- 

 acter of the gravelly clays upon which it rests, and in point of fertility it 

 ranks considerably below the prairie soil, and can only be successfully cul- 

 tivated by constant manuring or by judicious rotation of crops. It is an 

 excellent fruit soil, especially for apples and grapes, and the apple trees 

 generally appear more healthy and the fruit fairer than those planted upon 

 the level prairie. 



Another variety of soil to which I shall call your attention, and with 

 which many of you no doubt are familiar, is the soil of the Loess, or bluff 

 formation, as it is sometimes called. Extending in a narrow belt, covering 

 the bluffs on either side of all principal rivers, we find a deposit, ranging 

 in thickness from five to fifty feet or more, consisting of buff and gray 

 marly sand, frequently so coherent in structure that a cut of considerable 

 depth through it will retain its perpendicular walls for years, this coher- 

 ence being due probably to the carbonate of lime combined with the sili- 

 cious material. The calcareous matter in this deposit frequently leaches 

 out, by the prccolation of water through it, and forms irregular shaped 

 calcareous nodules, or fantastic concretions like the clay stones frequently 

 found in the stratified blue clays of the Connecticut valley. Along the 



