856 T. BELT ON THE STEFFE3 OF SOUTHERN RUSSIA. 



lusks, such as some of the species of Leda, that appear to thrive 

 best in water freshened by it. But even if these reasons were 

 sufficient for some parts of the northern continents, they would not 

 apply to the area in question. For when the country was almost 

 entirely covered by the sea, there could be few large rivers flowing 

 from it; and the melting of the northern ice could not cool water 

 in the latitude of the south of France so as to make it unfit for 

 animal life. 



Dr. Dawson has also pointed to the evidence, obtained by the 

 ' Challenger ' Expedition, that in certain areas of deep water there 

 is a possibility that an excess of carbonic acid may remove all trace of 

 calcareous organisms. This, however, only applies to abyssal depths ; 

 and the water that covered the south of Kussia nowhere reached 

 2000 feet, the extreme height that I can find anywhere in Europe 

 for the diluvial waters being about 1700 feet above the sea. The 

 preservation of the land and freshwater shells, as I have already 

 urged, also forbids us to believe that marine ones have beeji 

 destroyed. 



All the evidence and every line of argument seems to point to the 

 conclusion that the submergence was not marine, but that it was fresh 

 water that covered Central and Southern Russia, and sent up a great 

 arm into the valley of the Danube. In a former paper that I had 

 the honour to lay before the Geological Society, I put forward a 

 theory to account for the formation of a great continental lake or 

 sea of fresh water, that is in singular harmony with the requirements 

 of the present case*. It is that, in the Glacial period, the ice 

 accumulated at the northern ends of the Atlantic and Pacific Oceans, 

 and advanced southwards down the sea-beds, blocking up the 

 drainage of the continents as far as it extended. 



I shall not now enter on details as to the conditions under which 

 the ice accumulated, or the method and reason of its advance, as I 

 have already elsewhere treated these questions at length f ; but I 

 propose to show how far the theory explains the phenomena in the 

 district under consideration. 



From the north-east extremity of Asia to the Pyrenees there is a 

 range of high land, continuous excepting for two interruptions. 

 One of these is through the J3osphorus and Dardanelles ; the other 

 between the eastern end of the Pyrenees and the western spurs of 

 the Alps. The latter, I suppose, was blocked up by ice in the 

 Glacial period ; the former not cut through until after the forma- 

 tion of the great lake. To the north of this ridge the diluvial beds 

 are nearly everywhere spread out, up to heights of about 1200 feet 

 above the sea, and reaching to an extreme height of about 1700 

 feet ; to the south of it they are nowhere to be seen. According to 

 my theory, the basin so bounded to the south was completed by the 

 advance of the Atlantic ice on the coast of Europe, and by that of 

 the Pacific on the coast of Asia. The ice of the Pacific would hem 

 in the north-eastern outlet as soon as it advanced as far as the 



* Quart. Journ. Geol. Soc. vol. xxxii. p. 80. 



t Quart. Journ. of Science, January and July, 1S77 



