314 Si)' H. H. Hon-orth—The Baltic— The Litorina Sea. 



concliacea Helsingica," and he and others afterwards mentioned' 

 similar remains in other parts of Sweden. 



Lyell, in his well-known paper in the Phil. Trans, for 1835, 

 pt. 1, enumerated the shells he had found in these beds, whicli 

 (says Muntlie) is still a complete list so far as the Stockholm district, 

 is concerned. Of Mytiliis he had also found the small white flustrn, 

 now so commonly attached to them, in the Baltic. He also names 

 the Gasteropod Neritina fluvialilis, which lives in fresh and brackisli 

 waters. He lastly pointed out that the above-named fossil moUusca 

 are smaller than, and in some cases actually dwarf forms of, those 

 now living in the ocean, thus agreeing with the living Baltic shells. 



The enclosed character of the Baltic, which gives it its bracki>^h 

 quality, is an old physical feature of the sea, and it is not strange 

 that in the accumulations of estuarine mud and the raised shell-beds 

 on its shores we should be able to trace this characteristic of the sea 

 back in time to a considerable distance. When we examine these 

 beds, which consist partly of shell deposits and partly of estuarine 

 black clays containing molluscs, we shall find that the same features 

 which mark the living Baltic fauna have prevailed there for a 

 considerable time. We have a similar scanty fauna, and we have 

 also a series of shells which are more or less stunted or deformed. 

 It is nevertheless important to remember — and the fact was not 

 recognized by the older writers — that in these respects the living 

 shells considerably exaggerate the conditions prevailing in the shell- 

 beds. In the first place the lattei", although poor in species, are 

 richer than they would be if they were being deposited at this 

 moment. In addition to Tellina hallhica, in two forms which grade 

 into each other as now, Mytlhis edulis, Cardium edule, Palndinella 

 balthica, and the Bryozoan Memhranipora pilosa, we have in these 

 beds two species of Litorina, a Rissoa, and a worm iSpirorhis borealis. 



In regard to four of the species mentioned as found in the later 

 raised shell-beds of the coasts of the Eastern Baltic, it is an 

 important fact that they no longer live there. These are Litorina 

 litorea, Litorina riidis (since shown to belong to the sub-species 

 tenebrosa), a Bissoa (probably a small race of Rissoa membrnnacea) , 

 Scrobicularia piperata, and the worm Spirorbis borealis. None of 

 these shells are now found living east of the island of Bornholm, 

 and it was concluded by Loven that the reason is that the Eastern 

 Baltic has become less salt and in fact too fresh to admit of their 

 living there, for they continue to thrive in the Western Baltic. 



This conclusion was made a virtual certainty by the investigations- 

 of Munthe, who has shown not only that the shells last named 

 have been completely excluded from the living fauna of the 

 Eastern Baltic, but that the habitat of all the other marine species 

 now living there has been driven further south and nearer to the 

 supply of salt water, since the shells in the shell-beds were living. 

 He has further shown that in the interval each of these shells has 

 moved its habitat further south in a regular order and corresponding 

 to its capacity for tolerating a more or less mixture of fresh water 

 with salt. 



