arded as absolutely essential
to their vitality? Has not the same circulation been observed on the
surface of the earth which we have just contemplated in the
ocean,--the same incessant change, disturbance and restitution of
equilibrium?

Experience in agriculture shows that the production of vegetables on
a given surface increases with the supply of certain matters,
originally parts of the soil which had been taken up from it by
plants--the excrements of man and animals. These are nothing more
than matters derived from vegetable food, which in the vital
processes of animals, or after their death, assume again the form
under which they originally existed, as parts of the soil. Now, we
know that the atmosphere contains none of these substances, and
therefore can replace none; and we know that their removal from a
soil destroys its fertility, which may be restored and increased by
a new supply.

Is it possible, after so many decisive investigations into the
origin of the elements of animals and vegetables, the use of the
alkalies, of lime and the phosphates, any doubt can exist as to the
principles upon which a rational agriculture depends? Can the art of
agriculture be based upon anything but the restitution of a
disturbed equilibrium? Can it be imagined that any country, however
rich and fertile, with a flourishing commerce, which for centuries
exports its produce in the shape of grain and cattle, will maintain
its fertility, if the same commerce does not restore, in some form
of manure, those elements which have been removed from the soil, and
which cannot be replaced by the atmosphere? Must not the same fate
await every such country which has actually befallen the once
prolific soil of Virginia, now in many parts no longer able to grow
its former staple productions--wheat and tobacco?

In the large towns of England the produce both of English and
foreign agriculture is largely consumed; elements of the soil
indispensable to plants do not return to the fields,--contrivances
resulting from the manners and customs of English people, and
peculiar to them, render it difficult, perhaps impossible, to
collect the enormous quantity of the phosphates which are daily, as
solid and liquid excrements, carried into the rivers. These
phosphates, although present in the soil in the smallest quantity,
are its most important mineral constituents. It was observed that
many English fields exhausted in that manner immediately double