80 TRANSACTIONS OF THE ILLINOIS 



If I were asked to define in the briefest manner possible what con- 

 stitutes a soil, I should reply pulverized rock, for it is now a generally- 

 recognized fact that a large portion of our soils owe their immediate 

 origin to the rocks upon which they rest, and hence we see the intimate 

 relation existing between the soil and the geological structure of the 

 country. 



Now, in order to learn the mineral constituents of the soil, it will 

 be necessary for us to know what are the principal mineral ingredients 

 that enter into the composition of the rocks ; and when we examine 

 closely the rocky masses that go to make up the outer crust of the earth, 

 so far as they are accessible to human observation, we find them composed 

 mainly of three simple mineral substances, to wit : sand, clay and lime ; 

 and so, when we make a chemical analysis of the soil, we find that it 

 contains from 80 to 95 per cent, of these three minerals, the remaining 

 portion being composed of variable quantities of organic and inorganic 

 matter. 



In studying the character of the soil in any given locality, we might 

 first ascertain whether it had been formed from the decomposition of the 

 strata immediately beneath, or, in other words, from the bed-rock, or 

 from transported material that has been derived from some other region, 

 and now covers the former so deeply as to place it beyond the decompos- 

 ing influences of the atmosphere. In the latter case the soil would 

 probably possess a quite uniform character over considerable areas, 

 regardless of the changes that might occur in the character of the sub- 

 ordinate strata ; while in the former, the constituents of the soil would 

 change as we pass from one geological formation to another of a different 

 character, as from sandstone to limestone, and from the latter to beds 

 composed mostly of clay, as clay shales, argillites, etc. 



If we examine almost any portion of the country lying south of the 

 Ohio river, we shall find that the soil is generally derived directly from 

 the bed-rock, and consequently changing in its character and quality with 

 the changes that take place in the subordinate strata. In the winter of 

 1856 I had an opportunity of observing these facts, while traveling from 

 Mobile to the Ohio river, through Alabama, Tennessee and Kentucky, 

 and my attention was then first called to the' intimate relation that exists 

 between the soil and the geological formations beneath it, and I was then 

 impressed with the conviction that the geological structure of a country 

 determines to a great extent the avocations and wealth, and consequently 

 the intellectual, physical and moral condition of the people. In passing 

 up the river from Mobile to Tuscaloosa, over the outcrops of tertiary and 

 cretaceous rocks, the opportunities for satisfactory observations from the 

 deck of a steamer were by no means as good as could be desired ; but 

 notable changes could be seen even here, as we passed from the sandy 

 and argillaceous beds of these formations to those more highly charged 

 with calcareous matter. On leaving Tuscaloosa, however, by land con- 

 veyance, our course for nearly a hundred miles was upon the sandy shales 

 and sandstones of the coal measures. The soil was sandy and poor, the 

 surface brokec and hilly, from the soft and yielding character of the 



