178 M. Bronn on the Laws of Evolution of the Organic World 



But this is a difficult tlieory ; for the results of our investigations 

 in this direction can never be regarded as definitive, besides that 

 in this case we have probably to do only with very small chrono- 

 logical differences. 



The marine Pliocene beds also contain species of MoUusca 

 foreign to the previous periods (see Philippi, Wood, and D'Or- 

 bigny), united with others which already existed in the Miocene 

 period ; these have consequently made their appearance in the 

 course of the Pliocene epoch. The lacustrine Diluvian beds pre- 

 sent analogous facts as regards the terrestrial Mammalia. Bones 

 identical with Diluvian remains have been found in the sub- 

 Apennine Miocene sands and in the Mammaliferous crag of 

 England. But no one has yet succeeded (and perhaps no one ever 

 will succeed, from the want of constant characters) in determining 

 at what point in the Pliocene strata these latter species appeared. 



With the close of the Pliocene and Diluvian formations, the 

 last animal and vegetable species which became extinct, inde- 

 pendently of the action of man, disappeared ; for in the strata 

 of alluvium we only meet with the remains of species still actu- 

 ally in existence. It may, however, be objected to this view 

 that, in the most recent Pliocene strata, the number of extinct 

 species only reaching a very small per-centage, the determination 

 of the age must become very uncertain, owing to the organic 

 remains not being abundant. In fact, in this case it may easily 

 happen that the rare extinct species have not been preserved in 

 the locality under examination, although they may have been in 

 others. We consequently run the risk of regarding as alluvium, 

 strata which are in fact Diluvian or Pliocene, and of employing 

 as a proof, the very point which we have to demonstrate. We 

 are by no means sure that such errors have not been committed 

 in cases which have been employed to decide the question. 

 Lastly, how can we believe, after all the facts above cited, that 

 the last 5, 4, 3, or 2 per cent, of the extinct species of the Plio- 

 cene population ceased their existence at the same moment under 

 the equator and at the pole, at the bottom of the ocean and on 

 the surface of the continents ? 



This is a question as difficult to settle, as to know whether man 

 existed simultaneously with extinct species which have ceased to 

 exist without any historical intervention on his part, or whether 

 he has only appeared after their extinction. The appearance of 

 man, who has had so great an influence upon the present state 

 of our planet and upon the whole development of nature — the 

 entry upon the scene of the world of this " lord of the creation,^' 

 for whose reception all the rest could only have been a prepara- 

 tory woik, is an event which one would willingly have taken as 

 the starting-point of a new era in the history of the world. It 

 is true that human bones and fragments of artificial objects have 



