I G PALEONTOLOGY. 



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 Gaillonella 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, Actinocyclus, and 

 other silicious organisms. The lower part 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 statum of two miles 

 in length, and averaging twenty-eight feet in thickness, of 

 which the uppermost ten feet are composed wholly of the 

 sicilious shells of Infusoria, including the beautiful Campylo- 

 discus; the remaining eighteen feet consist of the shells mixed 

 with a pulverulent substance. Corresponding deposits of the 

 silicious cases of Infusoria have since been discovered in 

 many other parts of the world, some including fresh-water 

 species, others marine species of Infusoria. 



The conditions of such depositions will be readily under- 

 stood by examining the sedimentary deposits of bogs and of 

 stagnant or slow-flowing sheets of water. In warm latitudes 

 and seasons, such water swarms with infusorial life, and the 

 indestructible cases of the loricated kinds are found in great 

 quantities in the sedimentary deposits. Beneath peat bogs 

 they have been found to form strata of many feet in thickness, 

 and co-extensive with the turbary, forming a silicious marl of 

 pure whiteness. A quantity of pulverulent matter is deposited 

 upon the shores of the lake near Uranea, in Sweden, which, 

 from its extreme fineness, resembles flour : this has long been 

 known to the poorer inhabitants under the name of "berg- 

 mehl," or mountain-meal, and is used by them, mixed up with 



