214 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



in which he is universally acknowledged to occupy the highest rank, 

 has commenced a new series of essays under the title of ' Icono- 

 graphie des Coquilles Tertiaires reputes identiques avec les especes vi- 

 vantes, ou dans differ ens terrains de Vepoque tertiaire.' In the preface 

 to the first part he announces his views and object. He says that 

 he has been long convinced that the greater number of identifica- 

 tions of tertiary shells with those of other tertiary epochs, or with 

 recent species, are incorrect. From his investigations he is led to 

 maintain, 1st, that notable differences exist between living and ter- 

 tiary species ; and 2ndly, that in the tertiary formations the difi^erent 

 stages present distinct faunae. He opposes classification founded on 

 per-centages as purely artificial, and attributes the errors to the mis- 

 taking analogues for true identifications. He holds that each geo- 

 logical epoch is characterized by a distinct system of created beings 

 (the results of a new intervention of creative power), including not 

 only different species from those of the preceding system, but also 

 new types. At the same time he admits that the " reiterated inter- 

 vention of the creative power " does not necessarily and absolutely 

 imply a specific difference between the beings of different deposits. 

 He holds however the probability of such a difference existing, and 

 his object in this ' Iconographie ' is to prove that such difference 

 has been overlooked. He goes the length of saying, that, even when 

 species are, so far as the eye can judge, identical, they may not be so. 

 " Perhaps," he says, " there may exist species so nearly allied, as to 

 render it impossible to distinguish them ; yet even that would not be 

 to my eyes a proof of their identity ; it would only prove the insuf- 

 ficiency of our means of observation : " and further, " the animals 

 might differ though the shells are like." 



In the special part of his essay, M. Agassiz proceeds on the posi- 

 tion that the law of variation is not the same in all classes, families 

 and genera ; and selects his examples from certain genera of Ace- 

 phalous MoUusca in which the characters are very constant, viz. 

 Artemis^ Venus, Cytherea, Cyprina and Lucinn, on thirty-one forms 

 of which genera, considered by him as distinct species, he gives full 

 comments and valuable details. One species only among them, the 

 Cyprina islandica, he admits to be at the same time recent and 

 fossil. 



M. Agassiz introduces the same doctrine in his Monograph of the 

 Fishes of the Old Red Sandstone. Thus he says, at page xi, that the 

 characteristic fossils of each well-marked geological epoch are the 

 representatives of so many distinct creations, and affirms that he has 

 demonstrated '■'' pour un nomhre assez considerable d especes,'' that the 

 presumed identifications are exaggerated approximations of species 

 resembling one another, but nevertheless specifically distinct. 



Whether species of Mollusca hitherto deemed common to two or 

 more of the tertiary periods be really, as M. Agassiz affirms, distinct, 

 is a doctrine that must await the concurrence of experienced con- 

 chologists before it can be made the means of overthrowing present 

 generalizations, and the basis of new ones. With regard to the 

 Mammalia, certain eocene forms have been repeatedly recognised in 



