INTRODUCTION. XX1 
tinct 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Mammalia had been superseded by a new race, some of 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 Lophiodon and the Elephant; the 
raalivell oct cite: Clty 2 Ve 
