THE ANIMAL KINGDOM. ■ 29 



that, in spite of their extreme minuteness, some stratified 

 rocks, entirely made up of tlieir calcareous carapaces, 

 constitute at the present time mountains which take an 

 important place in the mineral crust of the glol^e. 



Again, microscopists have recently made known a wholly 

 unexpected fact. They have shown that some silicious 

 rocks, knoAvn by the name of tripolis, and Avhich to all 

 appearance were homogeneous, are almost exclusively 

 composed of the skeletons of several species of Infu- 

 soria belonging to the family of Bacillaria. These .skele- 

 tons have so faithfully preserved the form of the animals 

 from which they Avere generated, that men have been 

 enabled to compare them with our liAdng species, and 

 recognize that they had the closest analogy Avitli these. 



This remarkable discovery is due to Ehrenberg. He 

 commmiicated it to Al. Brongniai't on the occasion of 

 a journey the latter made to Berlin. This unexpected 

 revelation so excited the illustrious mineralogist that he 

 Avrote the folloAving words to the Academy of Sciences: — 

 "1 have seen all these marvels. I have compared them 

 Avith the beautiful drawings of living species made l)y M. 

 Ehrenberg, and I can no longer retain the .slightest doubt." 



Thus it is demonstrated that rocks Avhicli belong to the 

 most ancient epochs of life on our globe, and Avhich some- 

 times contain strata of vast magnitude, are only so many 

 graveyards of the Infusoria. The mind groAvs bewildered 

 in trying to find out in Avhat mysterious Avay so many 

 invLsil^le animalcules Avere aljle to form such extraordinary 

 heaps of corpses. 



The city of Eichmond, in North America, is the centre 

 of one of these districts, where, according to the l^eautifid 

 saying of Shelley, every grain of dust Avas once endued 

 Avith life. The deposit of microscopic .skeletons attains a 



