INTRODUCTION. XXI 



tirtct from any known existing Cetacea, and which, pro- 

 bably, like some of the eocene quadrupeds, retained fully 

 developed characters which are embryonic and transitory 

 in existing cognate Mammals. 



With the last layer of the eocene deposits we lose, in 

 this island, every trace of the Mammalia of that remote 

 period. The imagination strives in vain to form an idea 

 commensurate with the evidence of the intervening ope- 

 rations which Continental Geology teaches to have gra- 

 dually and successively taken place, of the length of time 

 that elapsed before the foundations of England were again 

 sufficiently settled to serve as the theatre of life to another 

 race of warm-blooded quadrupeds. The miocene strata of 

 the basins of the Danube and the Rhine, and the valley 

 of the Bormida, attest the share which the sea took in 

 the contribution of these deposits, between the end of the 

 eocene period and the time when we again find Mam- 

 malian fossils in England. Lakes and rivers intercalated 

 their sediments with those of the sea, as at Saucats, south 

 of Bordeaux ; whilst active volcanoes in Auvergne, Hun- 

 gary, and Transylvania, were adding their share of solid 

 matter to the rising continent.* 



Our knowledge of the progression of Mammalian life in 

 Europe during this period, is derived exclusively from 

 continental fossils. These teach us that one or two of the 

 generic forms most frequent in the older tertiary strata 

 still lingered on the earth, but that the rest of the eocene 

 Mammalia had been superseded by a new race, some of 

 which present characters intermediate between those of 

 eocene and those of pliocene genera. The Dinotherium 

 and narrow-toothed Mastodon, for example, diminish the 

 interval between the Lophiddon and the Elephant ; the 



* Lyell, loc. cit. ch. xv. 



