wn to exist 80 m. away from Lake
Aral, though they do not cross the Aral-Irtysh water-divide, so that
this sea will not probably have been at that time connected with the
Arctic, as some have supposed. The eastern limits of these deposits lie
about 100 m. from Lake Aral, though Severtsov maintained that they
penetrate into the basin of Lake Balkash. Southwards they have been
observed without a break for 160 m. from Lake Aral, namely in the
Sary-kamysh depression (the surface of which lies below the level of the
Caspian) and up the Uzboi trench for 100 m. from the latter sea. How
far they reach up the present courses of the Oxus (Amu-darya) and
Jaxartes (Syr-darya) is not known. Hence, it is plain that in late
Tertiary, and probably also in Post-Tertiary, times the Aralo-Caspian
Sea covered a vast expanse of territory and embraced very large islands
(e.g. Ust-Urt), which divided it into an eastern and a western portion,
communicating by one or two narrow straits only, such as on the south
the Sary-kamysh depression, and on the north the line of the lakes of
Chumyshty and Asmantai. More than this, the Caspian was also, it is
pretty certain, at the same epoch, and later, in direct communication
with the Sea of Azov, no doubt by way of the Manych depression; for in
the _limans_ or lagoons of the Black Sea many faunal species exist which
are not only identical with species that are found in the Caspian, but
also many which, though not exactly identical, are closely allied. As
examples of the former may be named--_Archaeobdella, Clessinia
variabilis, Neritina liturata, Gmelina, Gammarus moeoticus, Pseudocuma
pectinata, Paramysis Baeri, Mesomysis Kowalevskyi_ and _M. intermedia,
Limnomysis Benedeni_ and _L. Brandt_i, and species of the ichthyological
fauna _Gobius, Clupea_ and _Acipenser_; while as illustrating the latter
class the Black Sea contains _Dreissenia bugensis_ (allied to _D.
rostriformis_ and _D. Grimmi), Cardium ponticum_ (to _C. caspium), C.
coloratum_ (to _Monodacna edentula), Amphicteis antiqua_ (to _A.
Kowalevskyi_) and _Bythotrephes azovicus_ (to _B. socialis_).

In the opinion of Russian geologists the separation of the Caspian from
the great ocean must have taken place at a comparatively recent
geological epoch. During the early Tertiary age it belonged to the
Sarmatian Ocean, which reached from the middle Danube eastwards through
Rumania, South Russia, and along both flanks of the Caucasus to the
Aralo-Cas