ON INFUSORIA IN THE MUD OF RIVEES, ETC. G9 



deposits at Wismar, Pillau, Cuxhaven, the Nile, and some other similar 

 situations, shows that these organic forms amount to proportions 

 varying from ^th to ^-th of the whole deposit, or that the animal 

 deposition within harbours, in some cases where circumstances admitted 

 of an approximate measurement, amounts to many thousand cvvts. 

 annually. Such an announcement as this naturally excites the attention 

 of every microscopist, and leads him to see whether such results are 

 produced by all rivers, and if riot, to ascertain, if possible, the cause of 

 difference ; and it is not altogether unimportant to place on record every 

 fact, no matter how slight, bearing on so interesting a subject. 



The only opportunity for observation which I have heretofore had, is 

 as to the deposits of our own river, the Liffey. These, we know, are 

 very great in quantity, so much so as to entail a serious expense on the 

 curators of the navigation 'in maintaining dredging machines, for the 

 purpose of preventing their accumulation to an injurious extent. The 

 result of somewhat extended and very careful examination of these 

 deposits during the last month (Dec. 1841) is, that they do not at all 

 agree in character with those of the Elbe, and other rivers examined by 

 Ehrenberg. I find but very few specimens indeed of a few species of 

 Navicula, such as N. striatula, N. Hippocampus, N. sigma, N. viridis, 

 and some few others, and heretofore I have found but one solitary Poly- 

 thalamous shell ; in fact the organic forms do not constitute 10 1 00 th 

 part of the mass. 



Receiving then the announcement of Ehrenberg with all the confi- 

 dence which any observation of that eminent man deserves, we are 

 naturally led to inquire, Whence this remarkable difference ? 



The rivers, the deposits of which he has examined, flow for an im- 

 mense distance through flat alluvial districts. The Liffey, and its tribu- 

 tary, the Dodder, both have their sources in the granitic mountains of 

 the County of Wicklow, and within a very few miles reach the sea ; in 

 fact the waters of these rivers can be but a few hours in passing from 

 their source to the sea, and a small portion only of their limited course 

 is through alluvium ; and to this, J conceive, may be attributed the re- 

 markable difference. In the case of the long and slow rivers, the germs 

 of these minute beings, received most probably from the drainage of 

 the lands through which they flow, have time to attain maturity, and to 

 increase and multiply ; whereas, in the shorter and more rapid streams 

 this cannot be. 



It would be very interesting to examine the deposits of our great 

 river, the Shannon, flowing as it does through almost the whole length 

 of our Island, and, now sluggishly, now rapidly, through every variety 



