SOILS. 19 



them securely against waste from drainage or evaporation 

 for an indefinite time, till the growing crops demand them 1 . 

 They also greedily seize upon and hoard up all such fertil- 

 izing principles as are conveyed to them by the air and 

 rains. We may mention as an example of their efficiency 

 in abstracting vegetable nutrition from the atmosphere, that 

 many of them, when thrown out from a great depth below 

 the surface, and entirely destitute of organic remains (vege- 

 table or animal matter), after an exposure for some months 

 to its meliorating influence, become capable of bearing large 

 crops, without the aid of manure. This is particularly true 

 of the clays which rest on the Onondaga limestone, an ex- 

 tensive group occupying the central and north-western part 

 of New York. 



The clays are admirably adapted to the production of 

 most of the grains, and the red and white clovers cultivated 

 in the United States. These they yield in great profusion 

 and of the best quality ; and so peculiarly suited are they to 

 permanent meadows and pasturage, that they are styled by 

 way of eminence, grass lands. They are justly character- 

 ised as strong and lasting soils ; and when properly managed 



the purpose of still more clearly elucidating the subject to the mind 

 of the young student, we give some further examples. If we take a 

 piece of crystalized marble, compact uncry stall zed limestone, and 

 chalk, we shall have three substances exactly alike in their chemical 

 character ; for they are all chemical combinations of carbonic acid and 

 lime, associated together in precisely the same proportions. But in 

 their external arrangements, as they appear in a recent fracture to the 

 eye and touch, that is, in their mechanical arrangements, they are 

 totally dissimilar. 



Again If we take the pure lime, (quick lime),that is obtained from 

 each of the foregoing by subjecting them to an intense heat, by w"hich 

 the carbonic acid is expelled, and pour upon it nearly one third of its 

 weight of water, great heat is developed, and the lime both mechanical- 

 Zy absorbs, and chemically combines with it, forming a new compound, 

 or salt, which is a hydrate of lime. 



If sand (mostly silex) be added to the lime with water, and mechan- 

 ically mixed or stirred together and allowed to remain for a sufficient 

 time, they will combine chemically, forming silicate of lime, the 

 common mortar of stone masons. 



Sand (silex) stirred in with clay,(an impure alumina), is mechani- 

 cally mixed ; if then subject to a strong heat as in making brick, they 

 become chemically united, forming silicate of alumina, inseparable by 

 any human means short of. the chemists crucible. If we divide or 

 separate a stick by splitting or cutting, it is a mechanical; and if by 

 burning or charring, it is a chemical change. Thus every alteration, 

 either in nature or art, is referable to one of the above conditions or 

 changes. 



