It has been replied, In order to preserve it in a state of purity;
which is, however, untenable, mainly from the fact that organic
impurities in a vast body of moving water, whether fresh or salt,
become rapidly lost, so as apparently to have called forth a special
agency to arrest the total organised matter in its final oscillation
between the organic and inorganic worlds. Thus countless hosts of
microscopic creatures swarm in most waters, their principal function
being, as Professor Owen surmises, to feed upon and thus restore to
the living chain the almost unorganised matter of various zones. These
creatures preying upon one another, and being preyed upon by others
in their turn, the circulation of organic matter is kept up. If we
do not adopt this view, we must at least look upon the Infusoria and
Foraminifera as scavenger agents to prevent an undue accumulation
of decaying matter; and thus the salt condition of the sea is not a
necessity.
Nor is the amount of saline matter in the sea sufficient to arrest
decomposition. That the sea is salt to render it of greater density,
and by lowering its freezing point to preserve it from congelation to
within a shorter distance of the poles, though admissible, scarcely
meets the entire solution of the question. The freezing point of
sea-water, for instance, is only 3½° F. lower than that of fresh water;
hence, with the present distribution of land and sea--and still less,
probably, with that which obtained in former geological epochs--no very
important effects would have resulted had the ocean been fresh instead
of salt.
Now Professor Chapman, of Toronto, suggests that the salt condition of
the sea is mainly intended to regulate evaporation, and to prevent an
undue excess of that phenomenon; saturated solutions evaporating more
slowly than weak ones, and these latter more slowly again than pure
water.
Here, then, we have a self-adjusting phenomenon and admirable
contrivance in the balance of forces. If from any temporary cause there
be an unusual amount of saline matter in the sea, evaporation goes on
the more and more slowly; and, on the other hand, if this proportion
be reduced by the addition of fresh water in undue excess, the
evaporating power is the more and more increased--thus aiding time, in
either instance, to restore the balance. The perfect system of oceanic
circulation may be ascribed, in a great degree at least, if not wholly,
to the effect produced by the salts of the sea upon the mobility and
circulation of its waters.
Now this is an office which the sea performs in the economy of the
universe by virtue of its saltness, and which it could not perform were
its waters altogether fresh. And thus philosophers have a clue placed
in their hands which will probably guide to one of the many hidden
reasons that are embraced in the true answer to the question, “_Why is
the sea salt?_”