I 1- PALAEONTOLOGY 



(lass III. — INFUSORIA. 

 (Polygastria, Ehrenberg.) 



Numerous genera and multitudes of so-called specie* of 

 free and locomotive microscopic organisms, which, because 

 they do not present the distinctive characters of plants or 

 animals, have been by turns referred to one or other kingdom, 

 possess shells of flint, and consequently enter largely into the 

 domain of fossil evidences of former life. The silicious shells 

 of these infusory organisms present under the microscope the 

 most definite as well as beautiful characters of form and 

 sculpture, which are as recognisable and distinctive as those 

 of the calcareous shells of Mollusca. The plates of the incom- 

 parable works and memoirs of Ehrenberg abound with exaet 

 figures of the delicate sheaths, shells, and shields of the lori- 

 cated Infusoria of past and present seras of life, the deposits 

 of which, by reason of their pure, flinty, atomic constitution, 

 were known in the arts long before science had detected their 

 nature and vital origin. In 1S3G portions of the stone called 

 " tripoli " or " polierschiefer " (polishing-slate of lapidaries) 

 were microscopically examined by Ehrenberg, who discovered 

 it to be wholly composed of the silicious shells of Infusoria, 

 and chiefly of an extinct species called Gaillondla distans. At 

 Bilin, in Bohemia, there is a single stratum of polierschiefer, 

 not less than fourteen feet thick, forming the upper layer of a 

 hill, in every cubic inch of which there are forty-one thousand 

 millions of the above-named organic unit. This mineral like- 

 wise contains shells of Navicula, Bacillaria, Actinocydus, and 

 other silicious organisms. The lower pari of the stratum con- 

 sists of the shells compacted together without any visible 

 cement; in the upper masses the shells are cemented together, 

 and filled by amorphous silicious matter formed out of dissolved 

 shells. At Egea, in Bohemia, there is a stratum of two miles 



