INTRODUCTION. 



XI 



been destroyed, that is to say, the gelatinous or membraneous 

 portion which is mixed with the cretaceous part ; so that after its 

 destruction the shell is almost exclusively composed of calcareous 

 matter. It has lost its brilliance, its colours, and often even its mother 

 of pearl, if it had any, for it owed all these to the presence of the 

 animal part. It has generally become quite white, but sometimes, 

 having been long buried in a slime containing coloured particles, it 

 has acquired a peculiar hue, not its own. Other fossils have not only 

 lost the animal part, but even their substance has been transformed 

 into siliceous matter; in this case, the closer approximation of the 

 component parts leaves a small void space around the shell, in the 

 stone wherein it is imbedded, more or less interrupted by lateral 

 adherences. Shells have sometimes been so peculiarly disposed by 

 volcanic eruptions, as to preserve their natural colours even in the; 

 fossil state. 



We scarcely condescend to examine microscopic shells, from 

 their insignificant size ; but when we reflect that it is by means of 

 the smallest objects that Nature everywhere produces the most 

 astonishing and remarkable phenomena, they become highly in- 

 teresting, from their multiplication or abundance, and their conse- 

 quent influence on the composition and extent of the masses com- 

 posing the exterior crust of the globe. Whatever Nature may seem 

 to lose in point of volume in the production of such bodies, is 

 amply made up by the number of the individuals, which she mul- 

 tiplies with admirable promptitude to infinity. The remains of 

 these minute animals, therefore, have much more influence on the 

 surface of the globe than those of Elephants, Hippopotami, or 

 Whales. 



