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 evenits 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 every where 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. 
