1 86 ROMANCE OF LOW LIFE AMONGST PLANTS. 



variable in size and form, are superimposed, with a 

 band surrounding the margin, so as to leave a space 

 between them. When all that is soluble is dissolved 

 away the flinty skeletons remain, and these may be 

 preserved for ages in immense deposits, practically 

 indestructible, to testify to their previous existence. 

 When the older authors wrote of animalcules and 

 Infusoria, they for the most part included the dia- 

 toms ; the residue were chiefly foraminifera and radi- 

 olaria, but most of the silicious deposits consisted 

 mainly of Diatomaceae. 



" The stratum of slate, fourteen feet thick, found at 

 Bilin in Austria, was the first that was discovered to 

 consist almost entirely of minute flinty shells. A 

 cubic inch does not weigh quite half an ounce ; and 

 in this bulk it is estimated there are not less than 

 forty thousand millions of individual organic remains! 

 This slate, as well as the Tripoli, found in Africa, is 

 ground to a powder and sold for polishing. The 

 similarity of the formation of each is proved by the 

 microscope ; and their properties being the same, in 

 com.merce they both pass under the name of Tripoli. 

 One merchant alone in Berlin disposes annually of 

 many hundred tons in weight. The thickness of a 

 single shell is about the sixth of a human hair, and 

 its weight the hundred and eighty-seven millionth part 

 of a grain. The well-known Turkey stone, so much 

 used for the purpose of sharpening razors and tools ; 

 the rotten stone of commerce, a polishing material ; 

 and the pavement of the quadrangle of the Royal 

 Exchange, are all composed of infusorial remains." ^ 

 ' Jabez Hogg, "The Microscope," p. 431. (Sixth edition, 1867.) 



