POSTGLACIAL, &c, DEPOSITS OF CONTINENT 469 



Southern Norway, in the poverty of their organic remains. 

 They have yielded only five species of molluscs (Mytilus edulis, 

 Cardium edule, Tellina balthica, Paludina balthica, Littorina 

 litorea), all of which with one exception {Littorina litorea) still 

 occupy the brackish waters of the Baltic. The occurrence in 

 the same deposits of the common bullhead (Cottus scorpius), 

 which belongs to the littoral fauna of the Baltic, near Upsala, 

 and even so far in the interior as Skattmanso, sufficiently 

 demonstrates that the " black-clay " (Svartlera) of that region is 

 a littoral and estuarine formation. 



Now and again the postglacial clay becomes so abundantly 

 stocked with shells, that these may be said to form the major 

 portion of the deposit. Such shell-banks are frequently found 

 in Southern Sweden reposing upon the slopes of certain great 

 ridges of gravel called asar, which are of true glacial age. Erd- 

 mann makes special reference to a shell-bank which cloaks the 

 slopes of the as or gravel-ridge of Enkoping. This shell-bank 

 is not more than 100 feet above the level of the sea, and has all 

 the appearance of being a littoral accumulation, consisting as it 

 does of rapid alternations of gravel, sand, clay, and triturated 

 dSbris of the common mussel and Tellina balthica. But the 

 chief point of interest about it is the occurrence in the clay- 

 layers of plentiful remains of land-plants, such, for example, as 

 the stalks of Eauisctum limosum, leaves of the oak, the willow, 

 the aspen, needles and cones of the pine, twigs, branches, and 

 bark of the fir, the aspen, etc. The Equisetum, which still 

 grows abundantly along the shores of the Baltic, occurs without 

 doubt in the place of its growth — the margin of the ancient sea 

 — where its stalks became embedded year by year in the gradu- 

 ally-accumulating sediment. The other plant-remains had 

 evidently been washed down from the old land by running- 

 water. 



The postglacial shell -banks in the western districts of 

 Southern Sweden are often similarly grouped along the flanks 

 of prominent asar, but they never reach a greater elevation than 

 100 to 150 feet above the sea. Like those of the eastern region, 



