Ch. XIII] ARALO-CASPIAN FORMATIONS. 211 



The Tuscan blue marls of various localities, from which the above- 

 mentioned flora was obtained, have yielded 36 species of marine mol- 

 lusca, in which 16, according to M. Karl Mayer, are recent. 



Aralo- Caspian formations. — This name has been given by Sir R. 

 Murchison and M. de Yerneuil to the limestone and associated sandy 

 beds of brackish-water origin, which have been traced over a very 

 extensive area, surrounding the Caspian, Azof, and Aral Seas, and 

 parts of the northern and western coasts of the Black Sea. The 

 fossil shells are partly freshwater, as Paludina, JVeritina, &c, and 

 partly marine, of the family Cardiacice and Mytili. The species are 

 identical, in great part, with those now inhabiting the Caspian ; and 

 when not living, they are analogous to forms now found in the inland 

 seas of Asia, rather than to oceanic types. The limestone rises occa- 

 sionally to the height of several hundred feet above the sea, and is 

 supposed to indicate the former existence of a vast inland sheet of 

 brackish water as large as the Mediterranean, or larger. 



The proportion of recent species agreeing with the fauna of the 

 Caspian is so considerable, as to leave no doubt in the minds of the 

 geologists above cited that this rock, also called by them the " Steppe 

 Limestone," belongs to the Pliocene period.* 



* Geol. of Russia, p. 279. 



