298 
ARALO-CASPIAN OR STEPPE LIMESTONE. 
was bounded only by the mountains of the Hindoo Kusk and Chinese Tartary. On 
the north-east, north and north-west, however, we have ourselves to a great extent 
traced its boundary, as constituted by the palaeozoic and secondary rocks of Oren- 
burg, the extremity of the Ural chain, the cretaceous and older tertiary deposits on 
the right bank of the Volga, and the low hills of the Don Cossacks : whilst, along 
the northern shore of the Sea of Azof and the northern and western coasts of the 
Black Sea, the Aralo-Caspian strata are here and there seen to be underlaid, as at 
Taganrog, by the tertiary oceanic beds which have just been described. Of the 
southern boundary of this eastern Mediterranean, our personal knowledge does not 
range beyond the northern slopes of the rocky ridge of the Crimsea and the penin- 
sula of Taman. 
Pallas, the first propounder of the belief in a great inland retired sea, as well as 
several of his successors, have ascertained that similar deposits occupying the 
northern edge of the Caucasus, cover a great part of the isthmus between the Black 
and Caspian Seas, and we now know from MM. Eichwald and Dubois, that they 
spread over the country of Daghestan, a part of the low region east of Tiflis, and 
form the southern coasts of the present Caspian, beyond the limits of our Map. 
Throughout this enormous area scarcely any other strata are visible, except those 
which are charged with the relics of a former brackish sea, analogous to and often 
identical with species now inhabiting the present Caspian. 
By examination of the eastern tract of the Crimsea (Kertch, Taman, &c.) and the 
shores of the Black Sea, we satisfied ourselves that the chief strata of these loca- 
lities were formed beneath the same waters: and judging from the organic remains 
collected from numerous points of the whole area, there can be no sort of doubt, 
that all the masses of water now separated from each other, from the Aral to the 
Black Sea inclusive, were formerly united in this vast pre-historical Mediterranean ; 
which (even if we restrict its limits to the boundaries we already know, and do 
not extend them eastward, amid low regions untrodden by geologists) must have 
exceeded in size the present Mediterranean ! 
If towards the close of this work we venture to throw out a few speculations con- 
cerning the more active causes by which the relations of land and water have been 
changed, and by which this former expanse of water has been since converted into 
dry land, and separated into distinct seas now occupying different levels, our present 
object must be to describe the nature of the strata, their imbedded contents, and 
the altitudes at which they now lie. In so doing we shall also endeavour to show, 
