ELEMENTS OF SOILS. 229 



Oxide of iron. Iron is distributed throughout the mineral kingdom. The form which is 

 best known is the red oxide, or red rust of iron, of which there are two kinds, called pro- 

 toxide and peroxide. Both exist in some soils ; the first is recognized by its forming a dark 

 greenish precipitate with ammonia. The peroxide is found in the ashes of plants, and 

 when taken up, is combined either with crenic or phosphoric acid. The kernels of indian 

 corn contain iron ; there is, therefore, no doubt that it is an essential constituent of many 

 vegetables. 



Iron is invariably found in soils ; and in addition to its use to the vegetable, the color 

 which it imparts to the soil is of some moment. Red and brown soils absorb more heat 

 than light colored ones : they are said to be warmer. 



Oxide of manganese. Its color is black. It is not known as a necessary constituent of 

 vegetables. It gives a blackness to meadow soils sometimes ; but, so far as is known, it is 

 a neutral body : it may impart color to the petals of flowers. 



Silex composes the greatest bulk of the soil. It is the base or support of the mineral 

 kingdom : it is here, what carbon is to the vegetable kingdom. Its properties are modified . 

 by combination. Clay is the principal substance which counteracts the openness of sand. 

 The other elements of the soil, carbonate of lime, magnesia and oxide of iron, exert very 

 little influence mechanically upon it ; they, however, belong, as modifiers, to the siliceous 

 compounds, rather than to the argillaceous ones. 



V. CLASSIFICATION OF THE SOILS OF NEW-YORK. 



The ordinary course of observation among agriculturists has distinguished several classes 

 of soils in this State, and has recorded certain facts as associated with certain kinds of soil 

 adapted to a peculiar practice of husbandry. Such observations have been sufficiently 

 extended to lead to a general classification of the soils of the State. It was observed in 

 the southwestern part, of the State, that where the gravel and drift beds contained lime- 

 stone, wheat could be cultivated with success, and hence it was inferred that the limestone 

 region was especially adapted to the cultivation of this crop. Experience and observation 

 coincided in this case, and many good observers had drawn an imaginary line between the 

 wheat district and the grazing district. There is, however, an error in the observation, 

 which we shall point out in the sequel, although the error does not affect the principle of 

 the classification, as there is truly a wheat and a grazing district. 



The common classification of soils is founded on the predominance of certain elements, 

 which we have just described in the foregoing pages. Where, for example, silex pre- 

 dominates, the soil is sandy ; and where, on the contrary, clay predominates, it is called 

 argillaceous : a mixture of the two with organic matter, is called loam. To be still 



