ELEMENTS 
OF 
FOSSIL CONCHOLOGY. 
INTRODUCTION. 
Tue identification of the various formations of which 
the earth’s crust is composed, depends mainly upon a 
knowledge of the Fossil Remains imbedded in their strata. 
An acquaintance with these instructs us, that the globe 
which we inhabit has been subjected to many changes from 
one condition to another; for we find entire races of ani- 
mals have lived, perished, and become extinct, giving place 
to others, with an organic structure adapted to the altered 
conditions of our globe, at different epochs. 
Although the fossils which characterize any distinct for- 
mation, or series of rocks, have general characteristics, yet 
in the transition from the lower to the higher strata, a diffe- 
rence will be found in the species, and frequently in totally 
distinct genera, which are peculiar to each successive bed. 
In the Silurian rocks a striking modification of the dis- 
tribution of species has been remarked ; namely, that in the 
lowest beds the same species has been ascertained to per- 
vade a much greater thickness of strata in the lower than 
in the higher rocks, From which it would appear, that 
such Mollusks must have existed through much longer 
periods than any species of the newer deposits. And when 
A 
