level of the Caspian, however, was formerly about the same as the
existing level of the Black Sea, although now some 86 ft. below it. This
is shown by the evidences of erosion on the face of the rocks which
formed the original shore-line of its southern basin, those evidences
existing at the height of 65 to 80 ft. above the present level. That a
rapid subsidence did take place from the higher level is indicated by
the fact that between it and the present level there is an absence of
indications of erosive energy. There can be no real doubt that formerly
the area of the Caspian was considerably greater than it is at the
present time. Nearly one hundred and fifty years ago Pallas had his
attention arrested by the existence of the salt lakes and dry saline
deposits on the steppes to the east of the Caspian, and at great
distances from its shores, and by the presence in the same localities of
shells of the same marine fauna as that which now inhabits that sea, and
he suggested the obvious explanation that those regions must formerly
have been covered by the waters of the sea. And it is indeed the fact
that large portions of the vast region comprised between the lower
Volga, the Aral-Irtysh water-divide, the Dzungarian Ala-tau, and the
outliers of the Tian-shan and Hindu-kush systems are actually covered
with Aralo-Caspian deposits, nearly always a yellowish-grey clay, though
occasionally they assume the character of a more or less compact
sandstone of the same colour. These deposits attain their maximum
thickness of 90 ft. east of the Caspian, and have in many parts been
excavated and washed away by the rivers (which have frequently changed
their beds) or been transported by the winds, which sweep with
unmitigated violence across those wide unsheltered expanses. The typical
fossils unearthed in these deposits are shells of species now living in
both the Caspian and the Aral, though in the shallow parts of both seas
only, namely (according to Ivan V. Mushketov [1850-1902]) _Cardium
edule, Dreissena polymorpha, Neritina liturata, Adacna vitrea, Hydrobia
stagnalis_, in the Kara-kum desert, and _Lithoglyphus caspius, Hydrobia
stagnalis, Anodonta ponderosa_ and the sponge _Metchnikovia
tuberculata_, in the Kizil-kum desert. The exact limits of the ancient
Aralo-Caspian sea are not yet settled, except in the north-west, where
the Ergeni Hills of Astrakhan constitute an unmistakable barrier.
Northwards these marine deposits are kno