556 



FOSSIL ANIMALCULES. 



FIG. 627- FOSSIL REMAINS OF ANIMAL. 

 CULES, FORMING TRIPOLI. 



nally soft tissue of the body in a dry state. By exposing this 

 substance to a white-heat, the animal matter is driven off, and 

 the delicate siliceous shields are ootained in a perfectly unaltered 

 state. By this process it is found that about 25 per cent, of dry 

 animal matter is contained in the earth. In some of these col- 

 lections, the animalcules are of large size, their siliceous shields 

 measuring as much as -njVo of an inch in length. In the older 



strata of the tertiary formation 

 more extensive deposits are 

 found. One of the most re- 

 markable of these, is that which 

 is termed the Polierschiefer 

 (polishing slate) of Bilin ; this 

 supplies the tripoli used by arti- 

 sans in metal for polishing their 

 work, and also the fine sand 

 employed to form moulds for 



casting small articles of Berlin iron. For these purposes, Ehren- 

 berg estimates its consumption in Berlin only, at from 50 to 60 

 cwt. yearly. This deposit occupies a surface of great extent, 

 probably the site of an ancient lake, and forms slaty or laminated 

 strata of fourteen feet in thickness. It is almost entirely com- 

 posed of an aggregation of the siliceous shields of one of the 

 minute forms of fossil Infusoria, the Gaillonella distans. The 

 length of one of these is about o-J^- of a line, which is about -$ of 

 the thickness of a human hair. About 23 millions of animalcules 

 are contained in a cubic line of the Polierschiefer, and 41,000 

 millions in a cubic inch. A cubic inch of the Polierschiefer 

 weighs 220 grains ; and thus 187 millions go to a grain ; or the 

 siliceous shield of each animalcule may be regarded as weighing 

 about the 1 87 ooooo'o f a grain. The minuteness of these is 

 surpassed by that of the Animalcules of the Marsh Ochre, which 

 are only T oVo~ f a ^ me m diameter, y-J-j- part of the thickness of 

 the human hair, ^ of the diameter of a globule of the human 

 blood. A cubic line of such animal iron-ochre would thus, in 

 the same proportion, contain 1000 millions, and a cubic inch 

 upwards of 1,000,000,000,000 of living beings 



