ON THE CHOKING UP OF HARBOURS. 163 



the Baltic, and arrived at the following result, which he communicated to 

 the Societ^ des Amis des Sciences Naturelles, on the 18th of February, 

 1840; namely, that from -^th to th of the mass of deposited mud 

 consisted partly of living Infusoria, and partly of the empty shells of 

 siliciously enveloped and dead Infusoria. Last year, 1840, he repeated 

 these researches, and obtained a precisely similar result. 



In the harbour of Wismar, according to the documents which were 

 officially communicated by M. Rose, it appears that every week 36 lasts 

 of this mud are deposited, every last weighing 6000 Ibs. ; so that it may 

 be deduced, after seven and a half months of observation, that there is 

 an annual deposit of 1080 lasts, or of 32,400 metrical cwts., or of 6480 

 cubic metres. For a century, and probably more, matters have pro- 

 ceeded in this way without interruption ; so that during the last hun- 

 dred years, there have been deposited by the running waters at Wismar, 

 108,000 lasts, equal to 3,240,000 cwts., or 648,000 cubic metres of this 

 mud. Hence, then, supposing, which is very nearly correct, that ^th 

 of this mass consists of visible organic matter, there have been deposited 

 at Wismar, during the last century, of these microscopic silicious orga- 

 nisms, 64,800 cubic metres, or annually 648 cubic metres, which, when 

 dry, cannot constitute more than ^th, and probably not more than 

 Jg-th, or even less of the total weight. 



The results which have been obtained at Wismar in the year 1840, 

 suggested the idea to M. Hagen, to make similar experiments upon the 

 deposits at Pillau, and to communicate his observations. The speci- 

 mens of the deposits which he transmitted to M. Ehrenberg, are still 

 richer in organized beings than those of Wismar. They often consti- 

 tute, according to the result of forty experiments made upon different 

 samples, one-fourth, and sometimes even a half of the entire volume. 

 Hence it will follow, that at Pillau, also, there are annually separated 

 from the running waters, from 7200 to 14,000 cubic metres of pure 

 microscopic organisms, which in the course of a century would supply, 

 in this place alone, a deposit of from 720,000 to 1,140,000 cubic me- 

 tres of Infusory-rock or Tripoli- stone. 



Both at Wismar and Pillau there are to be met with in the organized 

 materials, some forms which are entirely new, and others which belong 

 to the waters of the ocean. As it regards the last-named harbour, 

 which is in the channel called Pillau-Haffe, the north wind often causes 

 the sea- water to flow into the river. 



M. Ehrenberg also alludes to the researches he made concerning the 

 muddy deposits of the river Elbe at Cuxhaven, and which were submitted 

 to the attention of the Berlin Academy in the year 1839. These muddy 



M 2 



