Sir E. H. Eoivorth—The Western Baltic. 461 



whenever a north - west gale prevails, a current setting in from 

 the ocean pours in a great body of salt water. Yet it seems 

 that during the whole time of the accumulation of ' the shell 

 mounds' the oyster flourished in places from which it is now 

 excluded. In like manner the cockle, mussel, and periwinkle, 

 which are met with in great numbers in ' the refuse heaps,' are of 

 the ordinary dimensions which they acquire in the ocean, whereas 

 the same species now living in the adjoining parts of the Baltic only 

 attain a third of their natural size, being stunted and dwarfed in 

 their growth by the quantity of fresh water poured by rivers into 

 that inland sea" ("Antiquity of Man," pp. 13 and 14). 



We can hardly doubt that the extinction of the oyster in the 

 southern waters of the Cattegat was due to the same cause which 

 exterminated the Litorinas, the Bissoas, and the Scrohicularia piperata 

 in the Eastern Baltic, which I have described at great length in an 

 earlier paper, namely, the breakdown of the land - bridge, which 

 affected the salinity of the water. 



Baer showed that the oyster cannot live in water holding more 

 than 37 parts in a thousand of salt or less than 16 or 17 parts; 

 and it seems plain that when the oysters were living in the Southern 

 Cattegat the waters of the latter, as Petersen urged, and as has been 

 generally conceded, were both salter and warmer. 



The oyster is not alone in having had to move further north- 

 ward, as is attested by the shell - beds and also by the kitchen 

 middens, which contain other edible molluscs. The typical form of 

 Cardium exiguum and Tapes pullastra, found with the oyster in the 

 raised beds and kitchen middens of the Southern Cattegat, have now 

 withdrawn to the Limfiord, and chiefly to its western part, which is 

 the most salt. 



Tapes pullastra still lives on the Swedish side of the Cattegat 

 with its relative T. aureus, but not further south than Bohuslan, 

 while T. decussatus, the most remarkable of all, which Steenstrup 

 found fossil at Kolindsund and in the Havelse and Mariager fiords 

 (see " Oversigterne over Videnskahemes Selskabs Forhandlungen,'^ 

 p. 188), is not found living now in either of the great fiords, nor in 

 fact south of Bergen in Norway. At Marieburg, Steenstrup also 

 found Pecten varius and species of Parthania and Odostomia, now 

 only living further north, as at Lighed and in the Limfiord. 



From the prevalence of several species of Tapes in the beds at 

 this horizon Petersen called them the Tapes beds. His view that they 

 argued a greater former salinity in the Southern Cattegat has been 

 generally accepted by the Scandinavian zoologists and geologists. 

 De Geer argued that the access of more salt water in ancient times 

 to what is forthcoming now was due to the fact of the Limfiord 

 having been open and there having been a continuous current through 

 it into the Baltic, but I cannot think this can ever have been the 

 controlling cause of such an important change. 



What reduces the salinity of the Southern Cattegat is the immense 

 outpouring of brackish water from the Baltic, the result of the vast 

 quantities of fresh-water continually pouring into it from its many 



