242 MOLLUSCA. 
trated. We know, with regard to the recent shells, that 
some species which are found in the bays of Norway and 
Greenland occur also on the shores of the Mediterranean, 
and that the British Isles have several species in common 
with Africa and the West Indies. Still we know not, with 
any degree of accuracy, the geographical range of any one 
species. Geologists ought, therefore, to exercise a great 
degree of caution in drawing conclusions concerning the 
original situation of those shells which they find in a fossil 
state. When a fossil shell is discovered in the strata of this 
country, which bears a close resemblance to the recent shells 
of distant seas ; many inquirers, without waiting until they 
have established the identity of the species, and without any 
precise information with regard to the geographical distri- 
bution of that species, conclude that this fossil shell must 
have been brought from these distant seas, and conveyed to 
its present situation by some mighty torrent. Instances of 
this mode of reasoning could easily be pointed out in the 
writings of British and Continental mineralogists. 
In every country there are particular animals and vege- 
tables, which indicate, by their mode of growth and rapid 
increase, a peculiar adaptation to the soil and climate of 
that district. Hence we find a remarkable difference in the 
animals and plants of different countries. Many shell-fish 
have indeed a very wide range of latitude, through which 
they may be observed; but we know, that the same mol- 
Juscous animals which are natives of Britain, are not found, 
as a whole, as natives of Spain, while the molluscous ani- 
mals of Africa differ from both. If the same arrangement 
of the molluscous animals always prevailed in the different 
stages of their existence, then we may expect to find the 
fossil shells of one country differing as much from those of 
