THE ANIMAL KINGDOM. 29 



structures of myriads of animals that we scour our cooking 

 utensils ! 



Not only do the Infusoria enter into the composition of 



13. Skeletons of Silicious Infusoria, seen under the microscope. 



the porous rocks, but we meet with them even in the most 

 compact that are known, such as the silex, which forms our 

 hardest pebbles and gun-flints. Mr. White, in a memoir 

 read before the Microscopical Society of London, described 

 twelve species in the flint of the chalk. 



The miraculous abundance of this once living dust in the 

 ancient epochs of our globe is fully shown in the coloring 

 of certain rocks. According to Marcel de Serre, rock-salt, 

 which is sometimes tinged with red, owes its tint to the 

 microscopic animals which lived in the waters wherein it 

 was formed. This savant also tells us that cornelians owe 

 their beautiful red color to the presence of Infusoria, a 

 fact irrefragably proved by an inspection of some of these 

 stones embedded in which the skeletons of different ani- 

 malcules can be discovered. 



