No marine deposits of later than miocene
age occur in or about it; and there is every reason to believe
that the Syro-Arabian plateau has been dry land, throughout the
pliocene and later epochs, down to the present time.
Raised beaches, containing recent shells, on the Levantine
shores of the Mediterranean and on those of the Red Sea, testify
to a geologically recent change of the sea level to the extent
of 250 or 300 feet, probably produced by the slow elevation of
the land; and, as I have already remarked, the alluvial plain of
the Euphrates and Tigris appears to have been affected in the
same way, though seemingly to a less extent. But of violent, or
catastrophic, change there is no trace. Even the volcanic
outbursts have flowed in even sheets over the old land surface;
and the long lines of the horizontal terraces which remain,
testify to the geological insignificance of such earthquakes as
have taken place. It is, indeed, possible that the original
formation of the valley may have been determined by the well-
known fault, along which the western rocks are relatively
depressed and the eastern elevated. But, whether that fault was
effected slowly or quickly, and whenever it came into existence,
the excavation of the valley to its present width, no less than
the sculpturing of its steep walls and of the innumerable deep
ravines which score them down to the very bottom, are
indubitably due to the operation of rain and streams, during an
enormous length of time, without interruption or disturbance of
any magnitude.
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