XXii INTRODUCTION. 
Anthracotherium and Hippohyus, that between Cheropo- 
tamus and Hippopotamus; the Acerotherium was a link 
connecting Paleeotherium with Rhinoceros. With these 
and other forms, as Halitherium, a kind of Dugong with 
molar teeth like those of the Hippopotamus, there like- 
wise appear a few genera that predominate in the pliocene 
strata, and which are still represented on the earth ; 
though by species quite distinct from those that existed 
during either of the tertiary periods. Our own island 
yields but a dim and confused indication of the geological 
operations that took place between the eocene and pliocene 
periods, in the wreck of strata that constitute part of the 
so-called Crag-formations on its eastern coast. In the 
oldest, and probably miocene portion, called the ‘“‘ Red- 
crag,” numerous remains of three or four extinct species of 
Cetaceous mammals occur ; but these were probably washed 
out of the subjacent eocene beds. From the Red-crag 
there have, likewise, been obtained a few rolled fragments 
of teeth referable to a Bear, to a species of Felis of the size 
of a Leopard, to a Hog, and a Deer. In the Norwich, or 
fluvio-marine Crag, referred by Mr. Lyell to his oldest 
pliocene period, there are found teeth and tusks of a Mas- 
todon of the same species as that which is associated with 
the Dinotherium in the miocene deposits at Eppelsheim ; 
and no remains of Mastodon have been found in any other 
formation in this island. This rare British Fossil Mammal, 
occurring in a deposit which is very near, if not identical in 
point of time, with the continental formations containing 
more abundant and perfect remains of the same Mas- 
todon, is a fact very analogous to that of the Chero- 
potamus and Anoplothere in our fresh-water eocene beds ; 
and is equally illustrative of the relation of particular 
species to particular epochs. 
