DISTRIBUTION OF THE MOtLUSCA IN TIME. 211 



exactly, SO as not to give the same name to bodies which, having- 

 apparent resemblances, are nevertheless distinct species, although 

 closely related. Such is the important connection of zoology 

 with geology. It is b}^ this double consideration that we shall 

 attain the aim of the latter science, which is the exact knowledge 

 of the relative antiquity of the beds which form the shell of the 

 globe.' 



" The views of William Smith are not less pointed : ' Organized 

 fossils are to the naturalist as coins to the antiquary ; they are 

 the antiquities of the earth ; and very distinctl}^ show its gradual, 

 regular formation, with the various changes of inhabitants in 

 the watery element.' 



" Whilst modern geologists recognize all the great principles 

 established by Buffon, Cuvier, Brongniart and Smith, they vary 

 in the interpretation of the laws of succession of living beings 

 upon the surface of the earth. • 



" One school, whichfhas had for its chiefs A. d'Orbigny and 

 Louis Agassiz, and which has perhaps borrowed from Cuvier 

 the basis of the doctrine, admits that living nature has been 

 renewed a great number of times, without the beings of one 

 period being able to perpetuate their specific existence into the 

 succeeding period. Consequently each period preserves for us 

 the remains of a special creation, terminated by a general cata- 

 clysm. Such is the theory of successive creations, which has 

 ruled during about a quarter-century and which has given a 

 remarkable impulse to palseontolog3^ 



"In the opposing school, to which are attached the names of 

 Brocchi, Constant Prevost, Boue, Lyell, d'Archiac, Gaudry, 

 Tournouer, and which, in certain points of view, approaches the 

 theories of Lamarck, of Geoff'roy Saint-Hilaire and of Darwin, 

 great cataclysms no longer exist as the general cause of the 

 destruction of life; their influence is purely local ; life has never 

 been interrupted, although modified during the series of ages. 



" In the appreciation of the fossils these two schools arrive 

 at nearly identical conclusions. For the school of multiple 

 creations, the fossil serves to characterize a period ; for the 

 developmental school, the fossil, by its more or less advanced 

 state of evolution, takes the place of a chronometer for judging 

 the antiquit}^ of the beds where it has been discovered. What- 

 ever may be the theory, it is admitted then as demonstrated, 

 that each period of life on the surface of the earth has been 

 characterized by living beings, the ensemble of which has differed 

 from that of the preceding and subsequent periods. Each 

 fossiliferous bed of importance may practically be considered as 

 representing a distinct creation ; consequently each period has 

 its peculiar fossils." 



A circumstance which gives to fossils a great importance as 



