MICE 0- ORGANISMS. 767 



mixture of these with a fine granular substance. Other similar de- 

 posits appear in many parts of the world. 



The many silicic clays owe their peculiar characters to the micro- 

 scopic fossils they have contained. The sands and tnergel of Sienna 

 and Coroncina, in Italy, imbed great quantities. The lanceolets, the 

 lowest of vertebrates, the mud-eating fishes, and the dirt-eaters among 

 men, subsist chiefly from these tiny organisms, for the so-called 

 " edible earths' 1 '' and " infusorial earths'''' are made up largely of, and 

 owe their nutritive qualities to, the remains of microscopic animals. 

 These earths are eaten in times of need by the Lapps and Tungu- 

 sians. They are likewise used in South America, in New Caledonia, 

 Kurdistan, in China, and in some of our own Southern States. The 

 " bread-stone " of China belongs to this kind of food. On the shores 

 of a lake near TJranea, in Sweden, there is a large deposit of infusorial 

 powder called Bergmehl (mountain-meal), which is mixed with flour 

 and eaten. It consists almost entirely of microscopic shells. 



The animalcules of plasma without a cover of cell-membrane are 

 known as rhizopods, or root-footed animals. These have been of the 

 greatest benefit in geological history. Those which have a central spore- 

 case are called radiolarians, and generally bear beautiful spheroid, radi- 

 ate, silicic frames, which have assisted largely in producing great flinty 

 deposits in the depths of the sea, constructing extensive masses of 

 rock. There is no doubt that they helped greatly in the formation of 

 the silicic rocks of Virginia, the Nicobar Islands, Sicily, Barbadoes, 

 etc. Indeed, this latter island consists almost entirely of their re- 

 mains, and two hundred and thirty-two kinds have been described on 

 it alone. Also the barren rocks, twenty feet thick, on which the city 

 of Richmond, Virginia, stands, consist mainly of their discoid shells. 



Other rhizopods, called foraminlfers, produce porous, calcareous 

 incasements for themselves and help form limestone rocks. 



Surprising as it may sound, it is nevertheless true that substan- 

 tially the rhizopods built the temples and mammoth pyramids of 

 Egypt and the stone walls of Vienna and Paris, for the very rocks of 

 these structures, as well as those which surround the Mediterranean 

 Sea and extend thence to the Himalayan Mountains, are chiefly built 

 up by their infinitely numerous perforated shells. There are extensive 

 limestone formations, which have resulted mainly from their remains, 

 and some of these bear their names, as the miliolithic, of the Paris 

 basin ; that of the Vienna basin ; the alveolithic, of western France ; 

 and the nummulithic, of the Mediterranean. Limestones composed 

 chiefly, sometimes entirely, of their shells, appear in the Grob-Kalk of 

 Gentilly and in very many other localities, also forming a broad belt 

 along both sides of the Mediterranean Sea and eastward therefrom, 

 sometimes hundreds of feet in thickness. 



But what is still more astonishing is the fact that the whole geo- 

 logical formation known as the cretaceous or chalk has been produced 



