Mammals, Birds, Reptiles, Fishes, Insects, and Molluscs, form the terrestrial fauna of the Eocene period. In the waters of the lakes, whose surfaces are deeply ploughed by the passage of large Pelicans, lived Molluscs of varied forms, as _Physa_, _Limnæa_, _Planorbis_; and Turtles swam about, as _Trionyx_ and the _Emides_. Snipes made their retreat among the reeds which grew on the shore; sea-gulls skimmed the surface of the waters or ran upon the sands; owls hid themselves in the cavernous trunks of old trees; gigantic buzzards hovered in the air, watching for their prey; while heavy crocodiles slowly dragged their unwieldy bodies through the high marshy grasses. All these terrestrial animals have been discovered in England or in France, alongside the overthrown trunks of palm-trees. The temperature of these countries was then much higher than it is now. The Mammals which lived under the latitudes of Paris and London are only found now in the warmest countries of the globe. The Pachyderms (from the Greek παχυς, _thick_, δερμα, _skin_) seem to have been amongst the earliest Mammals which appeared in the Eocene period, and they held the first rank from their importance in number of species as well as in size. Let us pause an instant over these Pachyderms. Their predominance over other fossil Mammals, which exceed considerably the number now living, is a fact much insisted on by Cuvier. Among them were a great number of intermediate forms, which we seek for in vain in existing genera. In fact, the Pachyderms are separated, in our days, by intervals of greater extent than we find in any other mammalian genera; and it is very curious to discover among the animals of the ancient world the broken link which connects the chain of these beings, which have for their great tomb the plaster-quarries of Paris, Montmartre and Pantin being their latest refuge. Each block taken from those quarries encloses some fragment of a bone of these Mammals; and how many millions of these bones had been destroyed before attention was directed to the subject! The _Palæotherium_ and the _Anoplotherium_ were the first of these animals which Cuvier restored; and subsequent discoveries of other fragments of the same animals have only served to confirm what the genius of the great naturalist divined. His studies in the quarries of Montmartre gave the signal, as they became the model, for similar researches and restorations of the animals of the ancient world, all over Europe--researches which, in our age, have drawn geology from the state of infancy in which it languished, in spite of the magnificent and persevering labours of Steno, Werner, Hutton, and Saussure. [Illustration: Fig. 151.--Palæotherium magnum restored.]