its of the rock particles to more distant areas and deposited them
over a subsoil that may be totally different in character from the surface
soil thus deposited.

_How Tillable Soil Is Made._--The action of plants themselves has a great
effect in adding to our supply of tillable soil. Seeds of plants or seeds
of trees become established in some slightly weathered rock areas and
begin to grow. The roots penetrate wherever there is any loose soil, and
partly by their pressure and partly through the acidity accompanying
decomposing plant tissue, complete a further breaking down of the rock.
There is a continuous process of destruction of rocks and leveling off of
mountains and hills to fill the valleys below.

Many groups of deep-rooted plants tend to increase the depth of the
surface soil by growth of the roots in the subsoil and by creating therein
a condition approaching that which already exists on the surface. The
action of earth worms and similar forms of life in bringing subsoil to
the top and in opening channels through which water and surface air can
penetrate constitutes another continually operating force in the creation
of a productive soil. A deeper layer of productive soil can also be
created through a plan of consistently deeper plowing, bringing up with
each annual plowing operation a small portion of subsoil which, when mixed
with the surface soil, tends to become like it.

[Illustration: (_Courtesy New Jersey Department of Conservation and
Development_)

Soil is created from rock by nature's weathering processes and by plant
growth. At the bottom may be seen solid rock; just above are
disintegrating rock fragments, and at the top, the soil.]

Every type of real soil contains all the elements of plant growth. This
plant food results from a breaking down of soil particles and the setting
free of chemical elements which, either singly or in combination, serve as
food for plants.

Whatever the type of soil may be, it will be found that certain crops will
make better growth in it than others. As a general rule, it may be said
that the only way to determine which plants will grow best on a given soil
is by the trial-and-error method. However, by observation of the growth on
similar types of soil we can learn something of a soil's crop
adaptability. There are some crops that will grow in almost any soil and
there are others that need an exactness of texture, moisture and plant
food which makes them hi