EHRENBERG ON INFUSORIA IN MARINE MUD. 253 



gation, only accumulates so far up as the flood tide is perceptible ; 

 but above this point, the bed of the river consists of pure siliceous 

 and other sand, it is evident, that the cause of this singular phe- 

 nomenon, which has hitherto not been sufficiently explained, is 

 principally owing to organic conditions. It appears, in fact, that 

 the mixture of river and sea water gradually kills vast multitudes 

 of the minute organic bodies, and causes them to fall to the bottom, 

 and form these accumulations. 



4. The marsh land of the lower district of the Elbe, below 

 Hamburg, and, probably, of all rivers flowing into the ocean, and 

 considered as humus, does not merely or even chiefly consist of 

 matter brought down by the stream from distant regions ; and still 

 less is it a local production of the minute animalcules existing in 

 river water, but it is to a very considerable extent derived from 

 organic beings existing in the ocean. 



5. If we deduct the admixture of fine sand as a matter of un- 

 certain origin, we shall find, not only at Cuxhaven, near the mouth 

 of the Elbe, but also at Giiickstadt, that from one quarter to one- 

 third of the mass of fresh mud is owing to the influence of marine 

 animalcules, and that above Hamburgh, as far as the flood tide ex- 

 tends, the proportion is about half as great ; but it has been 

 already shown, that what appears to be fine sand may also, in a 

 great measure, be an altered state of organic siliceous shells. 



The author has obtained similar results from the examination of 

 the mud of the Jahde in East Friesland and other places ; and in 

 a subsequent communication read to the Berlin Academy on the 

 27th November, 1843, he communicated the result of his further 

 inquiries on the same subject, in the lower districts of rivers, par- 

 ticularly the Elbe, the Jahde, the Ems and the Scheldt. 



In pursuance of his former investigations, the author proceeded 

 to Hamburgh and Cuxhaven, for the purpose of personally ascer- 

 taining the limits and extent of these phenomena. The river 

 bed of the Elbe at Magdeburg, both on the shore and islands, 

 consists of mere siliceous sand. Mud deposits of very slight 

 extent are first seen in the neighbourhood of Hamburgh, where the 

 river is divided by numerous islands into the Haasburg and Ham- 

 burgh Elbe. 



At Hamburgh, the author satisfied himself that these masses, 

 specimens of which supplied the groundwork of his former commu- 

 nications respecting marine organic life in the Elbe, formed the 

 chief integral mass of the islands known by the names of Reiher- 

 stieg and Kohlbrand. The channel has a depth of 7 — 8 feet at 

 the ebb, and rises at the flood 5 — 6 feet higher. The surface of 

 the islands is, generally, on a level with high-water mark, but in 

 many places it is about 5 feet higher. This gives a positive height 

 of the accumulated mud in the neighbourhood of Hamburgh, of 15 

 or 16 feet. The middle channel has a sandy bottom. 



Microscopic investigations have repeatedly shown, that in the 

 very smallest portions of this mud the siliceous skeletons of 

 marine animalcules are found, and that independently of all traces 

 of organisation, which may, and even must, have become obliterated 



