etions of testacea, zoophytes, and other
marine animals. But before muriate of soda can, in like manner, be
precipitated, the whole Mediterranean ought, according to the received
principles of chemistry, to become as much saturated with salt as Lake
Aral, the Dead Sea, or the brine-springs of Cheshire.

It is undoubtedly true, in regard to small bodies of water, that every
particle must be fully saturated with muriate of soda before a single
crystal of salt can be formed; such is probably the case in all natural
salterns: such, for example, as those described by travellers as
occurring on the western borders of the Black Sea, where extensive
marshes are said to be covered by thin films of salt after a rapid
evaporation of sea-water. The salt _atangs_ of the Rhone, where salt has
sometimes been precipitated in considerable abundance, have been already
mentioned. In regard to the depth of the Mediterranean, it appears that
between Gibraltar and Ceuta, Captain Smyth sounded to the enormous depth
of 950 fathoms, and found there a gravelly bottom, with fragments of
broken shells. Saussure sounded to the depth of two thousand feet,
within a few yards of the shore, at Nice; and M. Barard has lately
fathomed to the depth of more than six thousand feet in several places
without reaching the bottom.[459]

The central abysses, therefore, of this sea are, in all likelihood, at
least as deep as the Alps are high; and, as at the depth of seven
hundred fathoms only, water has been found to contain a proportion of
salt four times greater than at the surface, we may presume that the
excess of salt may be much greater at the depth of two or three miles.
After evaporation, the surface water becomes impregnated with a slight
excess of salt, and its specific gravity being thus increased, it
instantly falls to the bottom, while lighter water rises to the top, or
flows in laterally, being always supplied by rivers and the current from
the Atlantic. The heavier fluid, when it arrives at the bottom, cannot
stop if it can gain access to any lower part of the bed of the sea, not
previously occupied by water of the same density.

How far this accumulation of brine can extend before the inferior strata
of water will part with any of their salt, and what difference in such a
chemical process the immense pressure of the incumbent ocean, or the
escape of heated vapors, thermal springs, or submarine volcanic
eruptions, might occasion, are questions w