we can now prove that the vast amount of salt brought into the
Mediterranean _does not_ pass out again by the Straits; for it appears
by Captain Smyth's soundings, which Dr. Wallaston had not seen, that
between the capes of Trafalgar and Spartel, which are twenty-two miles
apart, and where the Straits are shallowest, the deepest part, which is
on the side of Cape Spartel, is only 220 fathoms. It is therefore
evident, that if water sinks in certain parts of the Mediterranean, in
consequence of the increase of its specific gravity, to greater depths
than 220 fathoms, it can never flow out again into the Atlantic, since
it must be stopped by the submarine barrier which crosses the shallowest
part of the Straits of Gibraltar.

The idea of the existence of a counter-current, at a certain depth,
first originated in the following circumstances:--M. De l'Aigle,
commander of a privateer called the Phoenix of Marseilles, gave chase
to a Dutch merchant-ship, near Ceuta Point, and coming up with her in
the middle of the gut, between Tariffa and Tangier, gave her one
broadside, which directly sunk her. A few days after, the sunken ship,
with her cargo of brandy and oil, was cast ashore near Tangier, which is
at least four leagues to the westward of the place where she went down,
and to which she must have floated in a direction contrary to the course
of the _central_ current.[458] This fact, however, affords no evidence
of an under-current, because the ship, when it approached the coast,
would necessarily be within the influence of a lateral current, which
running westward twice every twenty-four hours, might have brought back
the vessel to Tangier.

What, then, becomes of the excess of salt?--for this is an inquiry of
the highest geological interest. The Rhone, the Po, the Nile, and many
hundred minor streams and springs, pour annually into the Mediterranean
large quantities of carbonate of lime, together with iron, magnesia,
silica, alumina, sulphur, and other mineral ingredients in a state of
chemical solution. To explain why the influx of this matter does not
alter the composition of this sea has never been regarded as a
difficulty; for it is known that calcareous rocks are forming in the
delta of the Rhone, in the Adriatic, on the coast of Asia Minor, and in
other localities. Precipitation is acknowledged to be the means whereby
the surplus mineral matter is disposed of, after the consumption of a
certain portion in the secr