nd great summer
heats of Central Asia in more modern times. The desiccation of the
Aralo-Caspian basin, which communicated with the Black Sea only by a
comparatively narrow and shallow strait along the present valley
of Manytsch, the bottom of which was less than 100 feet above the
Mediterranean, must have been vastly aided by the erosion of the strait
of the Dardanelles towards the end of the pleistocene epoch, or perhaps
later. For the result of thus opening a passage for the waters of the
Black Sea into the Mediterranean must have been the gradual lowering of
its level to that of the latter sea. When this process had gone so far
as to bring down the Black Sea water to within less than a hundred feet
of its present level, the strait of Manytsch ceased to exist; and the
vast body of fresh water brought down by the Danube, the Dnieper, the
Don, and other South Russian rivers was cut off from the Caspian,
and eventually delivered into the Mediterranean. Thus, there is as
conclusive evidence as one can well hope to obtain in these matters,
that, north of the Euphrates valley, the physical geography of an area
as large as all Central Europe has remained essentially unchanged,
from the miocene period down to our time; just as, to the west of the
Euphrates valley, Palestine has exhibited a similar persistence of
geographical type. To the south, the valley of the Nile tells exactly
the same story. The holes bored by miocene mollusks in the cliffs east
and west of Cairo bear witness that, in the miocene epoch, it contained
an arm of the sea, the bottom of which has since been gradually filled
up by the alluvium of the Nile, and elevated to its present position.
But the higher parts of the Mokattam and of the desert about Ghizeh,
have been dry land from that time to this. Too little is known of the
geology of Persia, at present, to allow any positive conclusion to be
enunciated. But, taking the name to indicate the whole continental
mass of Iran, between the valleys of the Indus and the Euphrates, the
supposition that its physical geography has remained unchanged for
an immensely long period is hardly rash. The country is, in fact,
an enormous basin, surrounded on all sides by a mountainous rim, and
subdivided within by ridges into plateaus and hollows, the bottom of the
deepest of which, in the province of Seistan, probably descends to
the level of the Indian Ocean. These depressions are occupied by salt
marshes and deserts, in