252 GEOLOGICAL MEMOIRS. 



river. Their examination produced the interesting and decided 

 result, that the mud deposited by the Elbe, even at Gliickstadt, (a 

 distance of upwards of forty English miles distant from the mouth 

 of the river,) is completely tilled with the same microscopic marine 

 animalcules, possessing siliceous or calcareous skeletons, which, ac- 

 cording to a former report of the author, abound in the water at 

 the mouth of the Elbe, near Cuxhaven, and many of which were 

 figured in the Transactions of the Berlin Academy, in the year 

 1840. Thus these organic forms, which are better preserved at a 

 depth of several feet than on the surface, existed in the arable land 

 of the valley of the Elbe, which has been gradually accumulating 

 during many thousands of years, and in this way is explained the 

 origin of this soil in a more satisfactory manner than has hitherto 

 - been attempted. 



It was a matter of great interest to M. Ehrenberg to ascertain 

 how far up the Elbe this appearance of the direct influence of the 

 sea on recent formations of land (already known to extend as far 

 as Gliickstadt,) could be traced. The author, therefore, procured 

 several specimens of the mud of the river taken from three points 

 near Hamburgh, and three-quarters of a league higher up the river. 

 The examination of the river deposits at Gliickstadt and Ham- 

 burgh has proved the existence there of fifty-eight different species 

 of microscopic marine animalcules, mostly obtained in a livino- 

 state, and associated with many freshwater forms. 



Of this number, twenty-three are entirely new, and chiefly of 

 remarkable kinds, three of which seem to belong to new genera. 



The fifty-eight species thus obtained, consist of thirty-four 

 species of siliceous-shelled Polygastrica, twenty species of calca- 

 reous-shelled Polytlialamia, and four species of siliceous vegetable 

 remains, Phyto lith a r ia . 



Several of the forms collected near Gliickstadt in the river mud 

 still possessed their fresh ovaries, and must, therefore, have been 

 taken alive. The specimens collected at Hamburgh were only the 

 empty shells. 



Both series of observations give a great preponderance of marine 

 life over that of freshwater, and the species inhabiting the latter 

 are not described in the memoir, as they present no new forms. 

 The author gives the following as the results of his observations : — 



1. The minute microscopic animals of the sea extend up the 

 bed of the Elbe, (and this is probably the case, also, in all rivers 

 directly connected with the ocean,) as far as the ebb and flood of 

 the tide are perceptible. 



2. The flood-tide in the upper districts of the river, even where 

 the salt taste is no longer perceptible, as above Hamburgh, does not 

 consist merely of an accumulation of the river waters occasioned 

 by checking its outflow, but is now proved to be due to the direct 

 introduction of the sea water, probably under the river water, 

 and extending, very distinctly, as far as eighty English miles 

 above the mouth of the river. 



3. Since in the lower portion of the Elbe, the mud, consisting 

 of a mass of clay and slime, which often interferes with the navi- 



