THE BALTIC SEA 



291 



linking it with the North Sea. The Yoldian Sea was created with its Yoldia 

 (Portlandia) arctica, Area borealis, Mya truncata and other members of cold- 

 water Arctic fauna. 



So far it has not been finally determined whether the Yoldian Sea was con- 

 nected in the northeast with the White Sea through Lakes Ladoga and Onega. 

 Several authors (G. De-Geer, 1910 and more recently N. Jakovlev, 1926, 

 A. Arkhangelsky and others) considered that during the Yoldian Period there 

 was a wide connection between the Baltic and White Seas. Lately, however, a 

 number of authors (Munthe, Sauramo, Ekman and others) have denied such 

 a connection, considering that the Yoldian Sea did not extend eastwards be- 

 yond Lake Ladoga. The salinity of the Yoldian Sea fell far short of the salinity 

 of the ocean, and the Sea existed for a very short time (according to Munthe 

 for no more than 700 years, according to Sauramo for 500). 



Ancylus Lake Sea 



The rising of the dry land in the area of southern Sweden again separated the 

 Yoldian Sea from the ocean. For a second time the Baltic waters underwent a 

 loss of salinity, which turned the sea into the cold, strongly diluted Ancyl 

 Lake Sea (Fig. 1 34). This was populated by, among others, the fresh- water mol- 

 luscs Ancylus fluviatilis, Lymnaea, Unio and others, and had a strong outflow 

 to the west. G. De-Geer estimates the length of this phase to be 2,200 years. 



The Littorina Sea 



As a result of the subsidence of the bottom of the southwestern part of the 

 Baltic and a eustatic rise of the level of the ocean (Ramsay) a link was again 

 established with the ocean at the end of the Ancylus Period. Once more the 

 Baltic waters began to be more saline, and their salinity reached higher than 

 the present level (Fig. 136). This Littorina phase of increased salinity (Littorina 



Fig. 136. Surface salinity of the contemporary Baltic Sea (A) 

 and of the Littorina Sea (B) (Petterson). 



