76 



ERA OF THE TERTIARY FORMATION. 



having never ceased, the fauna had undergone such an amount 

 of change as naturalists are accustomed to describe (their 

 language being wholly arbitrary) as a renewal of species. 



It is in perfect harmony with this view, that from the com- 

 mencement of the Tertiaries, and as we ascend in the series, we 

 find more and more specific forms identical with those still 

 existing upon earth, as if we had now reached the dawn of 

 the present state of the zoology of our planet. By the study 

 of the shells alone, Mr. Lyell has formed a division of the 

 whole term into four sub-periods, to which he has given 

 names with reference to the proportions which they respec- 

 tively present of surviving species first, eocene; second, 

 miocene ; third, older pliocene ; fourth, newer pliocene. ( 40 ) 

 This division, however, is to be regarded as not safely appli- 

 cable to the Tertiaries generally, except as a convenient 

 means of indicating various portions of the series. 



The eocene period presents, in three continental groups, 

 1238 species of shells, of which forty-two, or 3*5 per cent, 

 yet flourish unchanged. Some of these are remarkable 

 enough ; but they all sink into insignificance beside the mam- 

 malian remains which the lower eocene deposits of the Paris 

 basin present to us, showing that the land had now become 

 the theatre of an extensive creation of the highest class of 

 animals. Cuvier ascertained about fifty species of these, all 

 of them long since extinct. About four-fifths are of the 

 order Pachydermata, thick-skinned animals, to which our 

 modern elephant, rhinoceros, horse, and pig belong. Nearly 

 the whole of these, however, belong to a family which is 

 now confined to South America and Sumatra, namely, the 

 tapirs, an animal of squat figure, and possessing a short pro- 

 boscis, an inhabitant of the woods, and. an herbivore, but of 

 unsocial habits. It is curious to find that a family now so 

 limited in its range, had formerly been distributed over 

 France, England, and other parts of the earth. Naturalists 

 have conferred the names, Palaeotherium, Lophiodon, Cory- 

 phodon, &c., upon the ancient extinct tapirs, which seem 

 chiefly to differ from modern species in a few peculiarities of 

 the constitution of the teeth, and in having three, instead of 



