and from the Black Sea, which has the same height as
the Mediterranean; and, on the east, from the Aral, 138 feet above
that level. The waters of the Black Sea, now in communication with the
Mediterranean by the Dardanelles and the Bosphorus, are salt, but become
brackish northwards, where the rivers of the steppes pour in a great
volume of fresh water. Those of the shallower northern half of the
Caspian are similarly affected by the Volga and the Ural, while, in the
shallow bays of the southern division, they become extremely saline in
consequence of the intense evaporation. The Aral Sea, though supplied by
the Jaxartes and the Oxus, has brackish water. There is evidence that,
in the pliocene and pleistocene periods, to go no farther back, the
strait of the Dardanelles did not exist, and that the vast area,
from the valley of the Danube to that of the Jaxartes, was covered by
brackish or, in some parts, fresh water to a height of at least 200
feet above the level of the Mediterranean. At the present time, the
water-parting which separates the northern part of the basin of the
Caspian from the vast plains traversed by the Tobol and the Obi, in
their course to the Arctic Ocean, appears to be less than 200 feet above
the latter. It would seem, therefore, to be very probable that, under
the climatal conditions of part of the pleistocene period, the valley
of the Obi played the same part in relation to the Ponto-Aralian sea, as
that of the Kishon may have done to the great mere of the Jordan valley;
and that the outflow formed the channel by which the well-known Arctic
elements of the fauna of the Caspian entered it. For the fossil remains
imbedded in the strata continuously deposited in the Aralo-Caspian area,
since the latter end of the miocene epoch, show no sign that, from
that time onward, it has ever been covered by sea water. Therefore, the
supposition of a free inflow of the Arctic Ocean, which at one time was
generally received, as well as that of various hypothetical deluges from
that quarter, must be seriously questioned.

The Caspian and the Aral stand in somewhat the same relation to the vast
basin of dry land in which they lie, as the Dead Sea and the lake of
Galilee to the Jordan valley. They are the remains of a vast, mostly
brackish, mere, which has dried up in consequence of the excess
of evaporation over supply, since the cold and damp climate of the
pleistocene epoch gave place to the increasing dryness a