on the Surface of the Earth. Ill 



their characteristic fossils, the ammonites and belemnites of the 

 Jurassic seas, as well as the genera and species which we find only in 

 the tertiary and modern formations ; — it would be necessary, in other 

 words, that all the facts collected by palaeontologists and geologists 

 for forty years should be considered as null and void. 



The second theory is that of the transition of species from one into 

 another. It assumes that the animals of recent epochs have all de- 

 scended, by direct generation, from the animals of the most ancient 

 epochs, and that the prolonged modifying action of exterior agents, 

 by perfecting or altering a long series of generations, is the only cause 

 of the differences that exist between different faunas. This theory is 

 founded on some facts which I have referred to above, and it sees, in 

 the circumstances to which we have traced the power of forming races, 

 forces sufficient to explain all the appearances of new types. Its 

 advocates think that the same agents, whose present action is limited, 

 and can produce only slight differences, may have exercised a more 

 powerful influence when nature was younger, and in a state of things 

 when the constitution of the surface of the globe was more variable 

 than it is now. According to these naturalists, the different forma- 

 tions contain, in their fossil remains, only the traces of the state at 

 which organism had arrived at the time when they were deposited. 



I shall not here enter into the detailed discussion of a theory 

 which I have already so often combated ; I shall merely state, that 

 the very slight modifications produced in our own day in species by 

 the prolonged influence of exterior agents, never exceeding the super- 

 ficial characters, are just a proof of the insufficiency of the variations 

 of these agents to alter essential characters. It is particularly to be 

 remarked, that the object is not to explain modifications of little im- 

 portance, but the existence, at all periods, of numerous types alto- 

 gether peculiar ; and that, in order to apply the theory in question, 

 it would be necessary to admit that reptiles of the secondary epoch 

 have had their ascendants in the fishes of the primary epoch, and 

 their descendants in the reptiles, and perhaps in the mammifera, of 

 our own epoch. We ought, in such a case, to seek the origin of the 

 cycloid and ctenoid fishes of our seas, in the ganoids of the secondary 

 epoch, and the forefathers of the latter in the anomalous fishes of 

 the primary epoch. We ought to admit that the diverse types of 

 mammifera are only transformations, by way of generation, from the 

 more imperfect animals which have preceded them, and that ele- 

 phants, rhinoceroses, &c., are the direct descendants of the pachy- 

 derms of the eocene period. It would, finally, be necessary that 

 man should look for his forefathers among some of the superior 

 types of the animal kingdom. Where are facts to be found which 

 justify such bold and extravagant fancies ? Are they not opposed to 

 all that observation teaches us ? 



There remains, then, the third theory, that of successive creations ; 



