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 asea 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 Navicule, 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 1834 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 ana- 
lysed by Klaproth, confirm anew. 
As the interest of this phenomenon 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, Eguisetum. 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 this 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. The specimens at hand from the Kritschelberg, near Bilin, ex- 
hibited so perfect a similarity, as well outwardly as in the forms of 
