Neighhourliood of' the Caspian Sea, 129 



fragments. Towards the upper part, this shell-limestone be- 

 comes grey and richer in fossils. Over this limestone there 

 lies a marl formation, which may be compared to the stratum 

 of marl which we have already remarked as lying deeper. It 

 is a grey, passing into a yellowish colour, and contains within 

 it a layer of calcined shells. The stratum of marl is almost 

 three feet thick from top to bottom ; the intermediate layer 

 of calcined shells is thinner. These shells lie here in a yel- 

 lowish marly limestone, which has sometimes a spongy, some- 

 times compact, texture. The shells are often found in the 

 marl itself. Their species is difficult to be made out, but 

 they resemble the Cardia. Upon the marl which is without pe- 

 trifactions, there lies a shell-limestone, which is rather of loose 

 texture, and of the nature of l^tiff": it has a whitish colour, and 

 is rather crumbly, and consists only of bleached or calcined 

 shells. The shells lie thickly together ; and here and there we 

 observe likewise yellowish oxide of iron collected in the cavities. 

 Sometimes the fragments of shells disappear ; and the limestone 

 becomes more free from petrifactions and more compact, assum- 

 ing a grey colour. This, then, is the highest stratum of lime- 

 stone which is found in the pass that is hollowed out of the 

 rock in which the fortress is situated. 



In this vicinity we find in some of the limestones Mytili and 

 a striped Glycymeris. The mytilus is very thick, and appears 

 to be distinguished, by well marked characters, from any of the 

 present species, and the same appears to be the case with the 

 Glycymeris. In other limestones, along with mytili, are fossils 

 resembling Cerithum. They are probably small Ceritha, which 

 may still, although as different species, occur in the Caspian 

 and Black Seas. In other limestone hills near Tarki, there are 

 some shells apparently belonging to the genus Corbula, and to 

 a species resembling those very frequently found at the estuary 

 of the Wolga, and probably also at Tereks. The above and 

 other details which might be laid before the reader, show that 

 much of the limestone is a shell-limestone tii/fof various tex- 

 tures, belonging to the newest tertiary period ; and which, along 

 with the older and similar formations on the east coast, belong 

 to an extensive lake of the tertiary period, as the same masses 



VOL. XIV. NO. XXVII. JANUARY 1833. 1 



