216 VARIATION OF SPECIES. [Ch. XIT. 



faluns of tlie Loire, not being aware that it differed in so many 

 important respects, especially in its approach to the living fauna of 

 the neighboring sea, from the French deposit. He was one of those 

 naturalists who advocated the doctrine that there was a complete dis- 

 tinction between the fossil species of periods standing next to each 

 other in chronological succession. Had he ranked the faluns as 

 Miocene and the Crag of Suffolk as Pliocene, he would not have as- 

 similated two forms so easily distinguishable. This we are entitled to 

 infer from his refusal to admit the specific agreement of any falunian 

 and living shells, and, what is still more remarkable, his refusing to 

 allow the existence of more than 44 recent species out of 437 in his 

 newer or Subapennine group. He divided the whole tertiary series 

 into five stages, each supposed to mark an era of repose on the earth's 

 surface, at the end of which all the living inhabitants were annihilated 

 by a great catastrophe, the earth being afterward repeopled with a 

 new set of forms. Even when he was forced to admit that one or two 

 in a hundred of the fossils passed from one formation to another, he 

 was inclined to attribute that small amount of agreement to the wash- 

 ing of dead shells from older into newer strata. This doctrine of the 

 absolute distinction of species in formations next in the order of suc- 

 cession would scarcely be worth referring to now that it is so generally 

 rejected by the most experienced geologists, were it not for the great 

 ingenuity with which some of its advocates have defended their views. 

 When the shells are confessedly undistinguishable, it has sometimes 

 been suggested, that if the soft parts of the animals had been preserved, 

 they would probably have been found to differ. On the other hand, 

 it is not uninstructive to note how easily palaeontologists of unques- 

 tionable merit can, if they are under the influence of a theory, such 

 as that above alluded to, find specific distinctions wherever they are 

 wanted, or, on the other hand, pronounce the same to have merely the 

 value of a variety. 



The points of difference expressed in the two figs. 162 b. and 163 

 may be regarded by the same zoologist as mere races or geographical 

 varieties so long as both are believed to belong to the same precise era, 

 but they will take the rank of species if one be regarded as Miocene 

 and the other as Pliocene. Specimens have occasionally been found 

 of this volute in the Coralline Crag which help to connect the Tour- 

 aine form with that of the Red Crag ; but it often happens in analo- 

 gous cases that no formation of intermediate age is extant, and then all 

 intermediate gradations, all evidence of there having been a passage 

 from one form to the other, and of both having had a common descent, 

 may be lost. Zoologists, whether they adopt or reject the theory of 

 the origin of species by natural selection, are still bound to be consist- 

 ent with themselves in regard to the amount of deviation from certain 

 types which shall be deemed sufficient to constitute a specific difference. 

 It is sufficiently difficult to arrive at philosophical conclusions when 

 the characters relied on are strictly those of the external forms and inter- 



