208 On the Fossil Shells of the Paris Basin. 



from the circumstance of plants being extremely favourable 

 to their preservation, that numerous terrestrial strata will 

 contain some traces of them. 



This is no less the case with many classes of invertebrate 

 animals, and among these, shells and zoophytes are the 

 most universally distributed. These bodies are seen in all 

 strata ; frequently distributed in great abundance ; and their 

 study well attended to, is an immense aid ; for they cannot be 

 examined with a view to the great question of their history, 

 without affording exact materials for the solution of the dif- 

 ficult question of the general and physical history of the 

 globe. 



To render useful services to the science of geology, it is 

 necessary that zoologists should apply themselves to the mi- 

 nute study of those fossil bodies, which are most universally 

 distributed. 



In this point of view, Conchology possesses an incontest- 

 able pre-eminence ; but it is unnecessary to defend a science, 

 which from the taste and zeal of its amateurs, has recently 

 become a fashionable study, more difficult however than 

 is generally supposed, and only conferring utility in its vast 

 applications in proportion as we descend to its minutest 

 details. 



This science, like all the other branches of Zoology, 

 implies an acquaintance with the intimate structure of 

 animals, so as to combine the character and affinities of 

 organization with the form of the solid body which the ani- 

 mal supports. It is after we have become acquainted with 

 all the facts detailed relative to living mollusca, that we can 

 arrive at a rational knowledge of fossil shells by means of 

 inductions sometimes difficult, in which we are guided never- 

 theless by recent shells. 



The inductions are first applied to the fossil species which 

 approach nearest to the living ; but in proportion as we des- 

 cend in the strata of the earth, the species differ more and 



