INFUSORIA AND OTHER ANIMALCULE. 251 



composed of Infusoria and Diatomacece which are 

 still living, and propagate daily with astonishing 

 rapidity. Their existence is doubtless maintained 

 by the waters of the river Spree, situated on a 

 higher level, which filter into the deposit. It 

 is feared that a period will arrive when a part, at 

 least, of the town will fall in, on account of the 

 rapid development of these microscopic creatures, 

 more especially the Gallionella, which, according to 

 Ehrenberg, form, in the space of four days, no less 

 than two cubic feet of new movable earth. 



The ' f polishing slate" of Bilin, in Prussia, which 

 is used for polishing metals, glass, marbles, etc., 

 forms a series of strata fourteen feet thick. It is 

 entirely composed of the siliceous shells of Infusoria 

 and Diatomacece, among which the most common 

 appear to be Gallionella distans and O. ferruginea. 

 One cubic inch of this polishing earth has been 

 shown, by accurate measurement and calculation, to 

 contain 41,000,000 individuals of G. distans, and 

 1,750,000,000 individuals of G. ferruginea (Figs. 32 

 and 33). In the present state of physiological 

 science it is impossible to say whether these 

 wonderful organisms are plants or animals. They 

 furnish us with an admirable polishing material, for 

 which it would be difficult to find a substitute.* 



* These and other fossil animalcules may be purchased in 

 London, from the different dealers in minerals, etc. Their structure 

 can only be discerned under a good microscope. 



