126 M. Eichwald's Geological llemarJcs upon the 



likewise only shells adhering closely together, almost without 

 any calcareous cement. It is, besides, of the nature of tiiff^ soft 

 and porous, since the shells leave empty spaces between them 

 throughout the whole mass. But since the shells lie so closely 

 together, their impressions are so obscure that we can scarcely 

 recognise their species. A mytilus appears to be most clearly 

 expressed. The remaining much more numerous impressions 

 of broken shells belong probably to the genus Venus^ still fewer 

 to the Card'tum tribe. Somewhat farther off, we find two hilly 

 summits, which have been employed by the Truchmen as a fort ; 

 this is constructed of masses of rock heaped above one another. 

 The rocky mass of these hill summits, which is soft, is likewise 

 of the nature of tuff; the fragments of shells are mostly loosely 

 aggregated, and scarcely united by means of a calcareous ce- 

 ment. But the shells are fine and thin, and completely cal- 

 cined ; here and there calcareous folia shine upon them, and all 

 of them resemble but one species of shell, of the genus Dcmaoc, 

 These shells adhere closely to one another, and by this means 

 form of themselves the shell-limestone. It is a striking circum- 

 stance, that this limestone likewise is composed of only one spe- 

 cies of shell. 



The rocky masses which prevail upon the high table-land si- 

 tuated between the Caspian and Aral Seas, border very much 

 upon the new formation of the hills of Tjukkaragan. Here 

 hills of marl and tertiary limestone everywhere occupy the sum- 

 mits and plains. Thus we see in a yellowish and tolerably firm 

 marl, decided Cardia, strikingly allied to Cardium edule; like- 

 wise small PaludincB, which are often only three lines long, as 

 they at present exist in the Caspian Sea. At other places the 

 marl becomes calcareous, and assumes a pure red colour, but 

 always contains the same Cardia and Paludlna. In other 

 pieces, on the contrary, which appear rather a pale yellow, 

 these two species, which entirely compose the calcareous marly 

 mass, are accompanied by small Ampullaria^ such as are abun- 

 dantly found in the tertiary limestone over the chalk formation 

 of Volhynia and Podolia. They are scarcely a line in length, and 

 a quarter of a line in thickness, but they do not live at present 

 in the Caspian or in the Black Sea. Lastly, much more remark- 

 able still is a calcareous marl, that consists entirely of Cyclada ; 



