44 NOTICES OF NEW BOOKS. 



existence of something like a series of distinct faunas. " The com- 

 parison of such faunas sometimes presents very important results, by 

 generalising from which certain supposed laws have been arrived 

 at, which it is assumed have governed the succession of organized 

 beings. Possibly these have been too hastily assumed, and the im- 

 portance of some phaenomena overrated ; but at any rate such gene- 

 ralizations have been useful, and they have greatly tended to advance 

 palaeontological science. It will be useful to consider what these 

 supposed laws are, and how far they are well-grounded. The num- 

 ber of the principal ones may be reduced to five, and we will exa- 

 mine them successively." — Vol. i. p. 57. 



Law 1. " The species of animals belonging to one geological epoch 

 have not existed either before or after this epoch, so that each for-- 

 mation has special fossils, and identical species are not found in 

 two formations of different age^. 



" Concerning this law, I believe that the progressive advance of 

 science will every day demonstrate more clearly its certainty and 

 generality ; but it is one not equally admitted by all geologists ; and 

 many, whose authority possesses great weight, consider that although 

 true with regard to the greater number of the species of each epoch, 

 yet that it is not generally true, since many species, as they sup- 

 pose, have been carried through, and are the same, from one epoch 

 to another. 



" The determination of the question thus at issue is a matter of 

 great interest in palaeontology, for upon the degree to which our 

 supposed law is admitted, depends entirely the opinion that will be 

 had of the application of this science to geology. If fossils are pe- 

 culiar to certain formations, they characterise them absolutely ; but if, 

 on the contrary, some are peculiar, while others are common to se- 

 veral groups of strata, a portion only of the whole number can fur- 

 nish us with results, and thence is introduced a source of consider- 

 able uncertainty and great chance of error. Those geologists who 

 have not admitted what may be termed the speciality of fossils, but 

 who at the same time are aware that these bodies must exercise an 

 inportant influence on the determination of formations, have made 

 a distinction between characteristic fossils, — those namely whose pre- 

 sence is looked upon as a certain criterion by which to mark the age 

 of a bed, and those, on the other hand, which are not characteristic, 

 or, in other words, are not capable of being made use of for such 

 purpose. But those naturalists who admit the speciality of fossils 

 regard them all as characteristic and as furnishing equally certain 

 results, provided only that they are distinctly made out. 



" In the discussion of this important law, palaeontologists do not 

 all start with the same data. M. Defrance indeed has assumed a sort 

 of special position in the study of fossil shells. In comparing them, 



* [This being a view altogether different from that taken by most English pa- 

 laeontologists, I have thought it better to translate literally the illustration of the 

 supposed law as given by the author. — Ed,] 



