INFUSORIA AND OTHEE ANIMALCULE. 263 



A similar deposit occurs in the Paris tertiary basin, 

 and in that of Brussels ; and it is not a little re- 

 markable that the fine-grained and easily-worked 

 limestone, which affords such an excellent material 

 for the decorated buildings of the French capital, is 

 almost entirely formed of accumulated masses of 

 the minute shells of foraminiferous animalculge. 

 Even in this Nummulitic limestone, the matrix in 

 which the Nummulites are imbedded is itself com- 

 posed of the more minute Foraminifera, and of the 

 broken and cemented fragments of the larger 

 species. 



It has often been remarked by chemists of 

 repute, that, in whatever manner carbonate of 

 lime was produced in the laboratory, nothing re- 

 sembling chalk has ever been obtained. The 

 mystery was solved when Ehrenberg showed us 

 that this substance is almost entirely composed of 

 fossil animalculge, of which he counted as many as 

 a million and a third in one cubic inch. 



The manner in which these microscopic fossils 

 may be rendered visible is thus : On a plate of 

 glass we place an extremely fine layer of chalk, 

 which, when perfectly dry, is covered over with 

 Canada balsam; and then, gently warming the 

 whole, we observe with a magnifying power of two 

 to three hundred diameters. 



Seventy-one species of these Foraminifera were 



