210 OYSTERS, AND ALL ABOUT THEM. 



those which, in their fossil state, constitute the chief bulk 

 of the chalk. (;/) 



" Beyond all doubt," adds Mr. Read, " the bulk of 

 the cretaceous series is composed of organisms still living, 

 as I have now shown, in our British seas, and, as Ehren- 

 berg observes, still capable, under the occurrence of favour- 

 able circumstances, of giving rise to the greatest changes 

 in the distribution of the solid crust of the earth. The 

 material, and not the magnitude of the infusoria, is the 

 proper element in these calculations. We must shut our 

 eyes to the minuteness of each individual atom of life, and 

 look rather at the marvellous activity of its law of increase, 

 and at its indestructible shield, which sets at defiance the 

 two great reducers of organic structures, death and fire. A 

 very few nutshells would hold all we should leave of an 

 elephant, if reduced to its ultimate elements by fire, but no 

 known intensity of heat would reduce the silicious mass of 

 infusoria. Fusion, under certain conditions, would be the 



(?z) The examination of a transparent slice gives a good notion of 

 the manner in which the components of the chalk are arranged, and of 

 their relative proportions. But by rubbing up some chalk with a brush 

 in water, and then pouring off the milky fluid, so as to obtain sediments 

 of different degrees ot fineness, the granules and the minute rounded 

 bodies may be pretty well separated from one another, and submitted 

 to microscopic examination, either as opaque or as transparent objects. 

 By combining the views obtained in these various methods, each of the 

 rounded bodies may be proved to be a beautifully-constructed calcareous 

 fabric, made up of a number of chambers, communicating freely with 

 one another. The chambered bodies are of various forms. One of the 

 commonest is something like a badly-grown raspberry, being formed of 

 a number of nearly globular chambers of different sizes congregated 

 together. It is called Globigerina, and some specimens of chalk con- 

 sist of little else than Globigerincz and granules. " On a piece of 

 Chalk," a Lecture to Working-men, by Professor Huxley. 



