T. BELT ON THE STEPPES OE SOUTHERN RUSSIA. 857 



mountains of Kamtschatka ; but that of the Atlantic would, on the 

 western side, have to reach the latitude of Northern Spain, and 

 coalesce with the ice of the Pyrenees or of the Cantabrian range, 

 to complete the basin on that side. 



The ice, as it advanced on the coasts of Europe and Asia, would 

 probably enclose to the north of the continents great areas of salt 

 water, so that the lake at first would be saline, but continually 

 freshening as it rose. This more or less saline water would first 

 reach the Aralo-Caspian region up the depression or great river- 

 valley by which the drainage of that area had flowed northward. 

 It is probable that it was at this time and by this channel that the 

 present arctic element in the Caspian fauna reached the Aralo- 

 Caspian area. As is well known, the Caspian at the present time 

 contains, along with many mollnsks that appear to be the de- 

 scendants of species of Cardiiim and Dreissena of the Congerian 

 strata, from which a few of them can scarcely be distinguished, some 

 vertebrates, crustaceans, and mollusks either identical with or very 

 closely allied to forms now living in the northern seas. Thus the 

 mammals are represented by a Seal (Phoca caspica) so nearly allied 

 to the Common Seal (Phoca vitidina), that many naturalists con- 

 sider them only varieties of the same species. Mr. Andrew Murray 

 says that so nearly allied is PJwca caspica to P. vitulina that, ex- 

 cepting for their geographical position, no one would think of sepa- 

 rating them *. Amongst the fishes of the Caspian there is Coregonus 

 leucichthys, a species also living on the northern coast. Amongst 

 the crustaceans there are many interesting relations shown with the 

 fauna of the Arctic Ocean. Amongst these I may mention Idoihea 

 entomon, which abounds in certain parts of the Caspian, and is found 

 in equal abundance in the Kara Sea to the north of Siberia. There 

 is also the Mysis relicta, another species of the northern seas, and 

 several other closely related species. Amongst the mollusks we 

 must, I think, omit Mytilus edulis, as it is contained neither in 

 Middendorff's nor in Grimm's lists, so that probably one of the 

 forms of Dreissena polymorpha has been mistaken for it. There 

 is no doubt, however, about the common Cockle (Cardium eclule), 

 nor of the variety rusticum, which is found on every coast of the 

 Caspian, and is also abundant in the White Sea. The presence of 

 these northern species has sometimes been appealed to as evidence 

 of a marine submergence ; but it is to be noted that they are all 

 known to live in brackish water, and most of them thrive in 

 waters less saline than that of the open sea. 



To this period, the first stage in the rising of the waters of the 

 great lake, I think the Newer Steppe Limestone of Murchison must 

 belong. I have not had an opportunity of studying it ; but Mur- 

 chison states that it forms the low steppes to the north of Astra- 

 khan, and that it contains the bones of the Mammoth. 



The nuviatile beds at Taganrog, and similar beds in the Lower 

 Danube, mark the continued rising and freshening of the water 



* Geographical Distribution of Mammals, p. 662. 



