OF THE ORGANIC FOSSILS. 435 



numerous species in the beds of Grignon, the inela- 

 nopsis, nautilus, distichopora, encrinus, oliva, conus, 

 tubipora, initra, voluta, nerita, paludina, and melania, 

 including nearly sixty species of marine and fresh 

 waters, abound as fossil in Europe, but, as living, 

 only in the tropical seas. But the value of this evi- 

 dence is by no means plain. It is first a question of 

 genera, not of species ; as it ought to be, if it were to 

 prove what is thought. There is a Coluber in Bri- 

 tain and there are many in hot climates. And no 

 animals are so notedly indifferent to temperature as 

 the mollusca. The Very same species of helix are 

 now found frozen in polar ice and broiling in the 

 African desert. Thus much for all these evidences 

 from the animals and plants themselves. 



But the hypothesis having been adopted, it was 

 also necessary to explain the causes : and having dis- 

 posed of the posteriori evidence, I must therefore ex- 

 amine the priori one. There is no provision for in- 

 terchange of climates in the present motions of the 

 earth : the axis cannot thus have changed under the 

 actual arrangement of the solar system. It is espe- 

 cially useless to assign so gratuitous a cause as the ap- 

 pulse of a comet, when the facts remain so much 

 more than doubtful ; and, if the argument from coal 

 be admitted, nothing. If it be said that the earth was 

 at first an irregular mass, and that it became sphe- 

 roidal only through a long series of changes, chiefly 

 through wear and renewal, and that thus any changes 

 of axis and climate can be accounted for, the answer 

 is the same. It is a pure hypothesis to account for 

 facts which, themselves, do not exist. 



Lastly, it has been said, in support of diminution 

 of temperature, not of interchange of climates, by 

 Button, De Luc, Breislak, and others, that this may 



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