Geology of' the Neig/ibourJiood of the Caspian Sea. 123 



with animal life, while the latter is very poorly stocked. This 

 particularly relates to those animals of the Caspian which live in 

 shells, and these are the proper inhabitants of this sea ; while 

 the fish, as fresh-water animals, mostly live at the mouths of the 

 larger rivers, and thus avoid the water of the sea containing sul- 

 phate of magnecia. 



Tjykkaragan,* — The calcareous chain of Tjukkaragan, upon 

 the east coast, rises close to the shore to a considerable height ; 

 farther to the south it gradually recedes from the coast. The 

 rock of this mountain- chain is a limestone, which, towards its 

 under strata, is without petrifactions, or it contains only a few 

 fossil shells ; while, towards its upper part, on the contrary, it 

 consists entirely of bivalve shells, which are so close together 

 that they quite compose the mass of the rocks. 



The compact limestone is mostly of a muddy white, or grey 

 colour; it also becomes bluish-grey, and then passes into a yel- 

 lowish tint. It is, however, not firm, but neither does it crumble. 

 Its grain is tolerably fine and compact ; but sometimes it becomes 

 compacter and firmer; however, it seldom contains petrifactions. 

 We see only here and there a shell differing somewhat from 

 the Cardium edule of the sea. This Gardlum appears to be 

 more drawn out lengthwise, and thus to be narrower ; the 

 valves are flatter, and the hinge-end is not so blunt as in the 

 Cardium edule ; the longitudinal streaks are besides very fine, 

 and not so coarse as they are in the Cardium edule or ru^ticum, 

 but the ribs, on the contrary, project prominently. The size of 

 most of them does not exceed a quarter of an inch. 



The yellowish-coloured shell-limestone is that which con- 

 tains the greatest number of petrifactions. In it well defined 

 Mytili and Doniaces accompany the small Cardium. The Mytili 

 differ but little from the Mytilus eduUs or polymorphus at pre- 

 sent living in the sea ; they have the same length, but with 

 a greater breadth, and are not so pointed. The Donaces, on 

 the contrary, are quite foreign to the Caspian Sea, and are only 

 found in the Black Sea. But the Donax triincnlus, which is 

 found alive in the Black Sea, is different in its external shape 

 from the fossil species found upon the east coast of the Caspian, 

 which is much smaller. There are likewise other shells, resem- 

 bling the VefiuSy varying in size, which appear, like the former 



