132 ON THE FILLING UP OF RIVER-BEDS AND HARBOURS. 



According to microscopical analysis, the mud of the harbour itself 

 contained from to *- of its volume of distinguishable organic bodies. 

 The sand taken from the navigable water outside of the harbour, ap- 

 peared to be principally granitic quicksand. 



The masses also deposited by the Vistula at Dantzic, and of which 

 four specimens were sent, taken from the bed of the river, at various 

 distances from the sea, according to a plan of the localities, were, indeed 

 not so rich in microscopic organisms as those from Pillau, Cuxhaven, 

 and Swinemiinde, but as those from Wismar, on account of the great 

 admixture of river sand, furnished only from about y^th to th of their 

 volume of organic remains. 



Marine forms, however, were found, at the point highest up the river, 

 and marked No. 4, and from this locality also, was furnished the ma- 

 terial least mixed with sand (Flugsand), and which was the richest in 

 Infusoria. 



Moreover the report, which was given in March of the results of in- 

 vestigation of the deposits of the Nile in Egypt and Nubia, in part fur- 

 nished by the examination by Dr. Hemprich, on the small portions of 

 earth adherent to plants collected in those countries, and the prospect 

 thus opened of the possibility of readily arriving at a knowledge of 

 these forms, from other and very distant parts of the earth, in a similar 

 way, had prompted Professor Kunth, in the most liberal manner to fur- 

 nish for microscopical examination, portions of earth which were adhe- 

 rent to some of the exotic plants in his rich herbarium. These mate- 

 rials were a portion of marine Conferva from the Falkland Isles, sent 

 by M. Lesson ; two specimens of Brazilian bog-earth (von Sellowschen 

 Grasern) ; a similar one from Peru, a portion of Conferva from the 

 Sandwich Islands, and from the Marian Isles, both sent thence by M. 

 Gaudichaud. All these materials, were respectively, as clearly from the 

 places indicated, as the plants to which they were still attached. 



Finally the author had received, by the kindness of the worthy tra- 

 veller in Iceland, Dr. Thienemann of Dresden, at his request specimens 

 of earth from Iceland, Labrador, and Spitzbergen. As the chief part of 

 these materials thus belong to the American hemisphere, their investi- 

 gation forms especially an addition to the " report, &c.," furnished on 

 the 25th of March.* 



From the examination in this way of the above mentioned particles, 

 often extremely small, or scarcely a line in thickness from those distant 



* Vide Ehrenberg's remarks, Vol. II., p. 26, of this Journal. 



