DISTRIBUTION OF MOLLUSCA IN TIME. 11% 
CHAPTER III. 
ON THE DISTRIBUTION OF THE MOLLUSCA IN TIME. 
THE historian of modern geology, Sir Charles Lyell, has taught 
us to regard the stratified rocks as so many monuments, record- 
ing the physical condition and living inhabitants of the earth in 
past ages. 
Each formation consists of a similar and more or less complete 
series of limestones, sandstones, clay, coal, and other strata, 
representing the deep and shallow seas, the fresh-waters, and 
the terrestrial portions of the surface of the globe, at one par- 
ticular period of time.* 
The organic remains found in the strata exhibit no such 
repetitions, but are changed gradually and regularly, from the 
earliest to the latest formations; so that the mass of species in 
each period must have been peculiar and distinctive. 
The important theory, that strata may be identified by fossils, 
was taught by William Smith, early in the present century, and is 
thus expressed in his Stratigraphical System:—‘‘ Organised fossils 
are to the naturalist as coins to the antiquary; they are the 
antiquities of the earth; and very distinctly show its gradual, 
regular formation, with the various changes of inhabitants in 
the watery element.”—‘‘ They are chiefly submarine, and as 
they vary generally from the present inhabitants of the sea, so at 
separate periods of the earth’s formation they vary as much 
from each other; insomuch that each layer of these fossil 
organised bodies must be considered as a separate creation ; 
or how could the earth be formed, stratwm super stratum, and 
each abundantly stored with a different race of animals and 
plants.’ + 
The ‘‘ Prodrome” of M. D’Orbigny is a catalogue of the shells 
(and radiate animals) of each formation, from which it appears 
that the mass of the living population of the globe has been 
changed twenty times since the close of the First or Palzeozoic 
Age; and although the fossils of the older rocks have not been 
generally classified with the same minuteness, yet enough is 
* The coal-measures and chalk of England cannot indeed be called similar, but the 
Cretaceous formations of the whole world afford mineral types, corresponding to, per- 
haps, every variety of Carboniferous rock. 
{ Stratigraphical System of Organised Fossils, 4to., Lond, 1817, 
