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 w r hich 

 they may be observed ; but we know, that the same mol- 

 luscous 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 



