PROF. EHRENBERG ON FOSSIL INFUSORIA. 401 



ness of the little siliceous shields made it indeed probable that an intense 

 heat had caused their accumulation from a more voluminous combus- 

 tible substance. But the opinion that they have belonged to the bottom 

 of a sea is improbable, since the chief part of the forms, both from their 

 figure and size, as well as from the number of their inner stripes, agree 

 very exactly with the Navicula viridis now living in all the fresh water 

 around Berlin, and widely diffused in other parts. In the sample of the 

 peat-bog there were also to be perceived Naviculae, which, though 

 mostly different from those of the Kieselguhr, were still living species, 

 and in quite a different proportion to one another, and generally in a 

 smaller proportionate quantity in the same space. 



After this the original specimens of the Kieselguhr from the Isle of 

 France, and the Bergmehl from San Fiore in Tuscany, in the Museum 

 of Berlin, which had been chemically analysed by Klaproth, and to 

 which were still attached the descriptions in his handwriting, were 

 microscopically examined. It was found that these substances also 

 consisted almost wholly of several different forms of fossil infusoria, 

 so that the whole siliceous contents given by Klaproth are to be assigned 

 to the infusoria shells. 



As early as the year ISS^ I announced to the Academy, in the ap- 

 pendix to my third paper on Organization, that, after having examined 

 with M. Henry Rose the discovery made by M. Kiitzing, that the 

 shields of the Bacillaria consist of silex, this fact was fully established, 

 not only for these, but also for other living forms ; a fact which the 

 observations of M. Fischer, and my examination of the Kieselguhr anar 

 lysed by Klaproth, confirm anew. 



As the interest of this phsenonienon appeared to be great, I com- 

 pared several other siliceous and earthy substances from the Royal 

 Mineralogical Cabinet, which Professor Weiss had the kindness to place 

 at my disposal, without however being able to forward the object of 

 the research. At a fortunate moment it occurred to me that such 

 siliceous shields might be in use in the arts as polish, like the siliceous 

 shavegrass, Equisetum. I purchased therefore in Berlin several kinds 

 of tripoli and polishing earths for examination. I examined first the 

 common or leaf tripoli, and found at once that this also consisted en- 

 tirely of the shells of infusoria. All the others were of a different 

 inorganic nature. A comparison of this tripoli of the shops (which, 

 as I was informed, comes from the Harz and Dresden) with the sci- 

 entifically arranged species of tripoli in the Royal Mineralogical Mu- 

 seum, showed that tliis so-called leaf-tripoli is evidently the same stone 

 which was received by Werner as a new species in mineralogy under 

 the name of Polirschiefer (polishing slate), which it has ever since re- 

 tained. Tlie specimens at hand from the Kritschelberg, near Bilin, ex- 

 hibited 80 perfect a similarity, as well outwardly as in tlie forms of 



