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