ANCYLUS LAKE 



207 



rounded whorls, becomes continually more conical, keeled, 

 and ridged, till at last it passes into the extremely modified 

 shell shown in the figure (Fig. 74). 



One point of interest presented by the freshwater shells 

 of the Levantine stage is their resemblance to those of 

 the west of America, on the one hand, and the south 

 of China on the other. Indeed, in the case of the existing 

 lake of Talifu, in the province of Junnan, South China, 

 this resemblance is so 

 great that Neumayr * 

 speaks of the lake as 

 the last survivor of the 

 Levantine series. 



In the Baltic we are 

 presented with a sea in 

 which marine species are 

 now undergoing a trans- 

 formation into brackish 

 water forms. During the 

 glacial period its basin 

 was filled with the ice of 

 confluent glaciers, and as 

 this began to melt away 

 its place was taken by 

 fresh water. A great lake 

 resulted, peopled by fresh- 

 water forms, of which 



the little freshwater limpet, Ancylus (Fig. 75), was one 

 of the most abundant ; hence the lake has been named 

 the Ancylus lake. Subsequently a subsidence of the 

 Scandinavian mass placed the Ancylus lake in communi- 

 cation with the North sea, which, as it entered, brought 

 with it a marine fauna. The saltness of the Baltic is 

 far from uniform, the water on the east side being much 

 '' Neumayr, " Erdgeschichte," vol. ii. p. 586. 



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