hich 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?]

By pursuing the prop