254 GEOLOGICAL MEMOIRS. 



after death, a proportional mixture of organic and chiefly solid 

 elements may be approximatively, if not quite accurately, ascer- 

 tained. This mixture may be assumed as amounting to not less 

 than aVth of the volume, so that in 20 cubic feet of matter from 

 the Hamburgh islands, there exists not less than 1 cubic foot of 

 animalcules, chiefly of marine origin, and provided with siliceous 

 skeletons. 



Another remarkable fact has resulted from these inquiries ; that 

 whereas during the month of July only the dead empty shells were 

 found near Hamburgh, the more recent researches have produced 

 many living marine animalcules, preserving their yellow-brown 

 and green ovaries in the natural healthy form and colour. The 

 author mentions Coscinodiscus radiatus, Actinoptychus senarius, 

 and Gallionella sulcata, as amongst the existing species found at 

 the Reiherstieg near Hamburgh ; but he states that he has never 

 found their forms in fresh water, either in the Elbe or in the Saale, 

 and of the two first genera, which contain upwards of twenty 

 species, none have ever yet been found in fresh water. 



M. Ehrenberg has ascertained by numerous inquiries, and from 

 various experiments, that no trace of salt could be detected in the 

 Elbe water, even at high tides, at Hamburgh, although such is the 

 case at Gliickstadt. Consequently as, notwithstanding this perfect 

 purity of the upper portion of the river water at Hamburgh, there 

 can be no doubt as to a considerable deposition, and even con- 

 tinued existence, of marine animalcules in this district, the author 

 can only explain the phenomena by assuming, that at high tides 

 the salt water not only drives back the fresh water, but that the 

 brackish water from the mouth of the Elbe also forces itself up the 

 stream with great power, in the manner of a wedge beneath 

 the fresh water, only stopping there where the tide ceases to flow, 

 probably near Zollenspieker or Lauenburg. 



Below Hamburgh, the influence of these minute animalcules in- 

 creases, and it even appears that the alluvial soil owes its greatest 

 fertility to their presence. The thickness of the bed in which 

 they there occur seldom exceeds 5 or 6 feet, and in this there 

 is much drift sand included ; but it remains still uncertain whether 

 this so-called drift sand may not. itself sometimes be derived from 

 the decay of siliceous -shelled animalcules and the siliceous portions 

 of plants. 



The examination of other specimens from the Scheldt, near 

 Antwerp, proved that there also existed in that river a similar 

 relation between the sea and river formations. There were here 

 found nine species of siliceous-shelled Potygastrica, and two species 

 of calcareous -shelled Polythalamia. With the exception of three 

 species, two of which were new, all these forms had been already 

 observed in the Elbe, near Cuxhaven, and afterwards near Gluck- 

 stadt and Hamburgh. 



It also appears from the examination of numerous specimens 

 from East Friesland, the districts of the Jahde and the Ems, and 

 the neighbourhood of Nordeney and other points of the coast, that 



