INFUSORIA 1 5 



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

 which the uppermost ten feet are composed wholly of the 

 silicious 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 T -fiowing 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 

 know T n to the poorer inhabitants under the name of " berg- 

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

 flour, as an article of food. It consists in great part of silicious 

 shells of Infusoria, with a little organic matter. With regard 

 to the source of fossil infusorial remains in sea-water, the fol- 

 lowing evidence is given in the United States Coast Survey, 

 1856 :— 



Soundings of the gulf-stream near Key Siscayne, Florida, 

 varying in depths from 147 fathoms to 205 fathoms, give a 

 light greenish-grey mud composed chiefly of Foraminifers, 

 Diatoms, Polycystins, and Geolites, in a profusion oidy sur- 

 passed by the fossil polycystinous strata of Barbadoes. The 

 Foraminifers compose the largest part of these muds, including 

 Texhdaria Americana, Marginu la Bachci, and other forms, 

 particularly many specie-, of the Plicatilia of Ehrenberg, 



