Neighbourhood of the Caspian Sea. 127 



the white shells of these are about two lines long, and appear to 

 be completely calcined. They lie so thick together, that they 

 compose the whole of the marl, and contain only single Paludina 

 between them. The species of Cyclada appears at present to 

 be a stranger to the neighbourhood, since I did not find it alive 

 any where on the east coast ; perhaps because rivers or low 

 standing fresh-water are almost no where to be seen. This 

 marl, therefore, forms an interesting tertiary fiesh-water forma- 

 tion^ which, without doubt, covers the above lacustrine shell' 

 liviestone. Lastly, I must mention a limestone of the nature of 

 roe-stone, which is mostly without petrifactions, but sometimes 

 contains remains of the above mentioned CycladcB ; hence it 

 must be contemporary with the fresh-water formation already 

 mentioned. It consists of very small concretions,, which lie 

 closely together, and among them are distributed fiagmeats of a 

 few shells. It might easily be mistaken for the roe of testaceous 

 animals or fishes, did it not occur in such great quantity. Be- 

 sides, this mass consists of carbonate of lime mixed with some 

 clay, and is sometimes of a reddish-brown, sometimes of a grey 

 colour. 



TarJci. — Near the sea-shore of Tarki, upon the west coast of 

 the Caspian Sea, there is a small hill, which consists of a com- 

 pact limestone. It is mostly of a greyish colour, rather passing 

 into black, and contains a great many small bivalve shells. The 

 shells have often disappeared, and oxide of iron is found collect- 

 ed in their empty cavities. Upon the shore itself there are a 

 great many fragments of shell -limestone, which are of a very 

 loose texture, and consist entirely of bleached or calcined shells. 

 The town itself is situated upon a high limestone rock, which is 

 rather rugged, and forms the last slope of the Caucasian chain. 

 In the rock of the fortress, we observe a very varied construc- 

 tion of the individual strata. From the principal street being 

 cut many feet deep in the rock, owing to this having been blast- 

 ed, we can thus observe very well the opposite strata of the dif- 

 ferent formations. The first formation which is here exposed, 

 is a tertiary limestone of a grey colour, or of a yellow and brown 

 mixed ; it has a splintery fracture, and is of considerable hard- 

 ness, but with single cavities, in which calcareous spar is collect- 

 ed. It contains no petrifactions. But upon this limestone there 



