Many terms, in general use among scientific men, and usually employed
in agricultural works, are obscure to young readers. For their sakes
we will explain some of them; and shall not be angry if _old_ men
profit by the explanation.
SOIL.—The surface-earth, of whatever ingredients it may be composed.
It may be a clay-soil, a sand-soil, a calcareous soil, as the surface
is composed of clay, or sand, or clay strongly mixed with lime, etc.
SUBSOIL.—The earth lying below the ordinary depth to which the plow or
spade penetrate. Sometimes it has hardened by the running of the plow
over it for a series of years; then it is called _pan_, as hard-pan,
clay-pan, etc. It is sometimes of the same nature as the top-soil, as
in clay-lands; in others it is a different earth; as when a coarse
gravel underlies vegetable mold, or when clay lies beneath sandy soil.
SUBSOIL PLOWING.—In ordinary plowing, the share runs from five to
seven inches deep. A plow has been constructed (called subsoil plow),
to follow in the furrow, and break up from six to eight inches
deeper—so that the whole plowing penetrates from ten to sixteen
inches.
SUBSOIL PLOW.—A plow having a narrow “_double share_, or a small share
on each side of the coulter, and no mold-board.” It is designed to
break up and soften the subsoil, but not to bring it up to the top.
MOLD.—A soil in which decayed vegetable matter largely predominates
over _earths_. Thus, leaf-mold is soil _principally_ composed of
rotten leaves; dung-mold, of dung reduced to a fine powdery matter;
heath-mold, a black vegetable soil found in heath-lands; peat-mold,
forest-mold, garden-mold, etc.
LOAM.—Clay, or any of the primitive earths, reduced to a mellow,
friable state by intermixture of _sand_, or vegetable matter, is
called loam. Clay lands well manured with sand, dung, or muck, are
turned, gradually, to a loam.
ARGILLACEOUS.—From the Latin (_argillaceus_,) soil principally
composed of clay.
ALUMINA OR ALUMINE.—Generally employed to signify _pure_ clay. It is,
chemically speaking, a metallic oxide; _aluminium_ is the metallic
_base_, and is an elementary substance.
It is generally known that the _diamond_ is pure carbon (charcoal is
carbon in an impure state), but it is not as generally known that the
_ruby_ and the _sapphire_, “two of the most beautiful gems with which
we are acquainted, are composed almost solely of alumina,” or pure
clay in a crystallized state.
SILICIOUS.—An earth composed largely of silex. _Silex_ or _silica_ is
considered to be a primitive earth constituting flint, and containing
most kinds of sands, and sandstones, etc. China or porcelain, ware is
formed from silica and alumina united, _i. e._ from silicious sand and
clay.
CALCAREOUS.—A soil into the composition of which lime enters largely.
Limestone lands are calcareous. Pure clay manured freely with marl
becomes calcareous, for marl is, mostly, clay and carbonate of lime.
ALLUVIAL.—Strictly speaking, alluvium or our alluvial soil, is a soil
formed by causes yet in existence. Thus a bottom-land is formed by the
wash of a river. It is usually a mixture of decayed vegetable matter
and sand.
DILUVIAL.—A diluvial soil or deposit is one formed by causes no longer
in existence. Thus a deposit by a deluge is termed _diluvial_. The
word is derived from the Latin (_diluvium_), signifying a deluge.
The terms argillaceous, calcareous, silicious, alluvial and diluvial
are constantly employed in all works which treat of husbandry.
FRIABLE.—A friable soil is one which crumbles easily. Clay is
_adhesive_, or in common language _clammy_: leaf-mold is friable, or
crumbling. Clay becomes friable when, by exposure to air or frost, or
by addition of sand, vegetable matter, etc., it is thoroughly
mellowed.