256 GEOLOGICAL MEMOIRS. 



hibits, when examined by the microscope, many vegetable remains, 

 chiefly Fuci and Zostera, and with them are found twenty species 

 of Polygastrica and one of Polythalamia, forming principal con- 

 stituent parts. This Darg is, therefore, decidedly a marine, and 

 not a freshwater formation, and contains the same forms of animal 

 life as those which now inhabit the North Sea. 



Moreover, M. v. Thiinen has found at a depth of 4 and 8 feet 

 in Jeverland, along the borders of an old island, a blue sand of great 

 fertility, which is collected and mixed with the arable soil. The 

 examination of this sand has proved that it also contains micro- 

 scopic organised beings, with calcareous and siliceous shells in 

 great abundance, and of the same genera and species which have 

 been above described. Thus it is no freshwater formation, but a 

 decided product of the sea. 



The author has also had an opportunity of examining specimens 

 from the Holstein marshes, chiefly from Brunsbiittel on the Elbe, 

 and partly from Wohrden, near the Eyder. At the latter spot, 

 the marsh soil 3 feet below the surface contains twenty-seven 

 species of siliceous-shelled Polygastrica, six species of siliceous 

 vegetable fragments (Phytolitharia), and one species of Poly- 

 thalamia, all of which, with two exceptions, Actwocyclus sol and 

 Surirella linea, are identical with species now living in the North 

 Sea at the mouth of the Elbe, near Cuxhaven, and most of which 

 extend as far as Antwerp. 



The author has lately found many of the above-mentioned North 

 Sea forms in the mud of the sea, and of the rivers near Liverpool 

 and Dublin, and many of them are also found in the Mediterra- 

 nean, where, however, the forms are, in general, very distinct. 



In conclusion, the author feels bound to remark that many of 

 the very numerous forms which are found so extensively distributed 

 along the coasts, and in the arable and marsh soils on the shores 

 of the North Sea as well as in the bottom of the North Sea itself, 

 are entirely wanting in the Baltic and along its coasts. Thus the 

 Tripodisci, the Tetrapodisci, the Nonionina germanica, Auliscus 

 and Cerataulus, together with Zygoceros and Geoponus Stella, 

 borealis, have not been found any where in the Baltic, nor in any 

 deposit along its flat shores, although most careful inquiries were 

 made throughout the whole basin of the Baltic, in Mecklenburg, 

 Pomerania, East Prussia, Finland, Sweden and Denmark. 



The author believes that, if these observations should, when 

 further carried out, prove any local distinction of forms, in conse- 

 quence of the greater extent to which most of the other species 

 can be traced, it will also appear less probable that the basin of 

 the Baltic Sea could ever have been in more direct communication 

 with the North Sea than it is at present ; and, likewise, that the 

 extensive beds of Infusoria at Kliecken, near Dessau, and at 

 Oberohe in Luneburg, which overlie the brown coal sand, cannot 

 by any possibility belong to the marine formations of the North 

 Sea, and that the greater deposits of the Spree and the Havel at 

 Berlin and Spandau, and on the banks of the Oder, near Freien- 



