244 UTILIZATION OF MINUTE LIFE. 



culiarity. This hard covering consists sometimes 

 of silica, and sometimes of carbonate of lime. To 

 it we owe the preservation of the forms of Infusoria 

 and Foraminifera (Rhizopoda), which have lain for 

 centuries upon centuries in a fossil state in the 

 strata of the earth. It has been calculated that 

 eight million individuals of Monas crepusculum can 

 exist within the space that would be occupied by a 

 single grain of mustard- seed, the diameter of which 

 does not exceed the one-tenth of an inch. 



Yet these myriads of little beings termed Infu- 

 soria have an important part to play in nature; 

 they help to keep the water they inhabit in a pure 

 state. They devour animal and vegetable matter 

 which otherwise would ferment, decompose, and 

 render the water putrid and unwholesome for the 

 use of superior animals. 



The flint- shelled infusoria, together with nume- 

 rous groups of lower beings (Diatomacece, Des- 

 midice, etc.) and the Foraminifera, form after death 

 considerable deposits at the bottom of the ocean 

 deposits which increase every day. In such a 

 material lies the transatlantic telegraph cable, and 

 by the progressive accumulation of these minute 

 organisms deprived of life, and the gradual pre- 

 cipitation of carbonate of lime, clay, etc., from the 

 water of the sea, the now soft muddy deposit thus 

 formed will, in course of time, become a hard rock. 



