on (he Surface of the Earth. 109 



on the mode in which the different faunas succeeded each other, may 

 appear only to throw the question farther back. I indeed admit, 

 that we thereby diminish its theoretical importance, and that we re- 

 ject the discussion of hypotheses relative to the succession of ani- 

 mals in that of the theory of successive creations. But I think that, 

 in a logical sense, it is necessary that a law, which ought to be 

 merely a simple generalisation of facts, should rest solely on obser- 

 vation, and be free from all hypothetical conceptions ; in other re- 

 spects the law, such as we here understand it, still preserves suffi- 

 cient importance, whether in a palseontological view, in which it 

 establishes one of the most remarkable facts in the history of the 

 globe, or in a geological point of view, for it is not necessary for the 

 geologist to solve the question as to the origin of beings, but rather 

 to determine whether the fossils studied by ordinary zoological me- 

 thods all differ from one formation to another, and, consequently, 

 that they may all serve to characterise formations, or whether a cer- 

 tain number of them only can be regarded as characteristic shells. 



I admit, then, that the law of the specialty of fossils consists in this, 

 that each formation contains fossils which differ from all those of other 

 formations, at least, that they differ from each other as much as the 

 beings now existing in nature which we consider as different species. 

 Now, as I have stated above, I regard this fact as indisputable within 

 certain limits, and that to deny it totally is to reject the most direct 

 lessons of observation. No species (assigning to that word the value 

 given above) is found at the same time in the formations of the pri- 

 mary epoch, and in those of the secondary, any more than in one of 

 the latter, and also in the tertiary epoch. No species is common to 

 the pennine, triasic, Jurassic, or cretaceous formations. These im- 

 portant and essential facts, admitted by all geologists, and which form 

 the basis of the science, are sufficient to establish the existence of 

 this law. 



But if it be indisputable when expressed in these general terms, it 

 is also true that it is more difficult to fix its limits. MM. Agassiz, 

 D'Orbigny, &c., and numerous palaaontologists after their example, 

 extend it to all the subdivisions of the crust of the earth known under 

 the name of formations, such as the five or six Jurassic stages, the 

 five cretaceous stages, the three tertiary stages, &c. I believe, with 

 them, that the more the science advances, the more will it confirm 

 this method of regarding it ; but a complete demonstration can only 

 result from a more perfect science, and it is to the illustration of this 

 essential point that the principal efforts of pala3ontologists ought to be 

 directed. I have already shewn elsewhere (Paleontology i., 64), 

 that a multitude of erroneous assimilations have been made, and I 

 believe that the attacks upon this law are very often owing to the 

 imperfect determination of fossils, or a bad classification of formations, 

 whose limits have been sometimes misunderstood, and the subdivisions 

 too greatly multiplied. In every case, and whatever may be the 



