RELATIVES OF THE OYSTER. 213 



acquires as great force as the proof derived from the nature 

 of the chalk itself. (/>) 



The extreme minuteness of the chalk animalcules is 

 strikingly proved by the fact that, even in the finest levi- 

 gated whiting, multitudes of them are still present, and 

 may be applied, without suffering change, to the most 

 varied purposes. Thus, in the chalk coating given to 

 painted chambers, paper, or even glazed visiting cards, 

 may be seen a pretty mosaic of well-preserved moss-coral 

 animalcules, invisible to the naked eye. Our natural vision 

 receives from such a surface the impression of the purest 

 white ; it is only the microscope that can disclose the fact, 

 that it contains the bodies of millions of beings of exceed- 

 ingly varied and beautiful forms that once enjoyed life. 

 .Similar relics are found in the series of the oolite and lias 

 rocks, which come under the chalk, and, in England and 

 many other countries, overlie the new red sandstone. 



Another instance, too remarkable to be omitted, is 

 that of the polishing slate of Bilin, in Bohemia, occupying 

 a surface of great extent, probably the site of an ancient 

 lake. Its slaty stratum, fourteen feet in thickness, consists 

 almost entirely of an aggregation of silicious shields of one 

 species of animalcule, Gaillonella distans. These shields, 

 or cuirasses, as they have been called, are most beautiful 

 coverings, sometimes of a single plate, sometimes double, 

 formed of the purest quartz or rock crystal, and therefore 

 perfectly transparent. 



The size of one of these animalcules amounts, on an 

 average, and in the greater part, to one two-hundred-and- 

 eighty-eighth of a line, which equals one-sixth of the 

 thickness of a human hair. The globule of the human 



(p ) " On a piece of Chalk," by Professor Huxley. 



