Is the same kind of rock always of the same composition?
How do rocks differ?
The relation between the inorganic part of soils and the rocks from which it was formed, is the foundation of Agricultural Geology. Geology may be briefly named the science of rocks. It would not be proper in an elementary work to introduce much of this study, and we will therefore simply state that the same kind of rock is of the same composition all over the world; consequently, if we find a soil in New England formed from any particular rock, and a soil from the same rock in Asia, their natural fertility will be the same in both localities. Some rocks consist of a mixture of different kinds of minerals; and some, consisting chiefly of one ingredient, are of different degrees of hardness. Both of these changes must affect the character of the soil, but it may be laid down as rule that, when the rocks of two locations are exactly alike, the soils formed from them will be of the same natural fertility, and in proportion as the character of rocks changes, in the same proportion will the soils differ.
What rule may be given in relation to soils formed from the same or different rocks?
Are all soils formed from the rocks on which they lie?
What instances can you give of this?
In most districts the soil is formed from the rock on which it lies; but this is not always the case. Soils are often formed by deposits of matter brought by water from other localities. Thus the alluvial banks of rivers consist of matters brought from the country through which the rivers have passed. The river Nile, in Egypt, yearly overflows its banks, and deposits large quantities of mud brought from the uninhabited upper countries. The prairies of the West owe a portion of their soil to deposits by water. Swamps often receive the washings of adjacent hills; and, in these cases, their soil is derived from a foreign source.
We might continue to enumerate instances of the relations between soils and the sources whence they originated, thus demonstrating more fully the importance of geology to the farmer; but it would be beyond the scope of this work, and should be investigated by scholars more advanced than those who are studying merely the elements of agricultural science.
The mind, in its early application to any branch of study, should not be charged with intricate subjects. It should master well the rudiments, before investigating those matters which should follow such understanding.
In what light will plants and soils be regarded by those who understand them?