254 -4w Explanation — Geology of Ohio. [June, 



been transformed into soils, or have supplied the materials of the 

 secondary rocks, from which, by decomposition, the greater portion 

 of soils have been produced. These inorganic elements consist of 

 potash, soda, lime, magnesia, manganese, iron, silica and alumina. — 

 But while these elements are distributed with considerable regularity 

 in the primary rocks, so as to supply to soils thence derived, in 

 due proportion, all the elements essential to the growth of vegeta- 

 tion, yet such is not always the case in the secondary rocks, or in the 

 soils derived from them. In the analysis of the feldspars, micas 

 and Iwrnhlendes, associated with the quartz of the primary rocks, we 

 find the alkalies, the iron and alumina' always present ; but in the 

 secondary rocks such uniformity rarely ever prevails. For example: 

 in the sandstones, often, there is too great an excess of silica to afford 

 permanently productive soils ; in the slates there is generally an 

 excess of alumina, so as to supply little else than clay to their soils ; 

 but the limestones, in their decomposition, aflFord an abundance of 

 lime, which, of all the alkalies, is the one most essential in giving 

 the greatest fertility to lands. 



The organic elements essential to vegetation are oxygen, hydrogen, 

 nitrogen and carbon, and are constituents of or embraced in the 

 atmosphere ; sulphur and phosphorus are intermediate elements, 

 also essential to vegetation, which are universally distributed in 

 soils — the former mostly in abundance, the latter sparingly. 



Now, the diminution in the fertility of lands, as we stated, may be 

 due to one of three causes, or to all combined. One or more of 

 the inorganic elements, in such a state as to be taken up by vegeta- 

 tion, being sparingly present in soils, may become exhausted by 

 cultivation ; or there may be a deficiency of the organic elements 

 present in the soils, to promote the proper chemical changes in the 

 inorganic elements, so as to adapt them to the absorbents of the 

 growing vegetation ; or there may be a sufficient supply of both of 

 these classes of elements in soils, and a deficiency exist in the sul- 

 phur and phosphorus, when the results may be equally unfavorable 

 to the maturing of crops. 



With the statement of these facts, it will be readily understood, 

 why the geologist, upon learning the true geology of any district, 

 can give an opinion, proximately correct, as to its fertility ; and 

 you will understand, also, the importance of a knowledge of the 

 geology of the country intersected by this railroad, to the distant 

 friends of the enterprise. With soils containing the basis of an 



