The genus Equus is represented as far back as the latter part of the Miocene epoch; but in deposits belonging to the middle of that epoch its place is taken by two other genera, Hipparion and Anchitherium; and, in the lowest Miocene and upper Eocene, only the last genus occurs. A species of Anchitherium was referred by Cuvier to the Paloeotheria under the name of P. aurelianense.
Far back in the distant Eocene Epoch of our planet's history, the Colorado was the outlet of an inland sea which drained off toward the Pacific, as the country of northwestern Arizona rose; and the Grand Cañon illustrates, on a stupendous scale, the system of erosion which, in a lesser degree, has deeply furrowed the entire region.
The Zeuglodons from Eocene down to Pliocene, the Dolphins in the Pliocene, and the Ziphoids Catodontidae, and Balaenidae in the Pliocene, are all fully developed forms, with no intermediate species. Eohippus Lower Eocene of America; fore-feet have four toes and a rudimentary thumb or pollex. 2. Anchitherium Eocene and Lower Miocene; three toes, but 2 and 4 are diminutive. 4.
As a matter of fact, in modern man's wild chase after wealth and pleasure, it is only one person out of every ten thousand who pauses to regard such causes, unless cornered by some protectionist fanatic, held fast and coerced to listen. We are not discussing the animals of the Pleistocene, or the Eocene, or any period of the far-distant Past.
There can be little doubt that even the talcose granite or gneiss of Mont Blanc itself has been in a fused or pasty state since the flysch was deposited at the bottom of the sea; and the question as to its age is not so much whether it be a secondary or tertiary granite or gneiss, as whether it should be assigned to the Eocene or Miocene epoch.
In all the essentials of its very peculiar structure, the Macropoma of the Chalk is identical with the Coelacanthus of the Coal. Look at the genus Lepidotus, again, persisting without a modification of importance from the Liassic to the Eocene formations inclusively.
I formerly dissented from this division, but I now find that I must admit it to be the only one which will agree with the distribution of the Miocene mammalia, while even the mollusca of the Fontainebleau sands, which were formerly supposed to present at preponderance of affinities to an Eocene fauna, have since been shown to agree more closely with the fossils of certain deposits always regarded as Middle Tertiary at Mayence and in Belgium.
Croll believes that the last great glacial period occurred about 240,000 years ago, and endured, with slight alterations of climate, for about 160,000 years. With respect to more ancient glacial periods, several geologists are convinced, from direct evidence, that such occurred during the miocene and eocene formations, not to mention still more ancient formations.
But these newly-discovered records do not fill up the wide gap, some of them being closely allied to the Eocene, and others to the Cretaceous type, while none appear as yet to possess so distinct and characteristic a fauna as may entitle them to hold an independent place in the great chronological series.
This stone-embedded relic of the moth that sucked the juices of the plants of the Mesozoic world, incalculable ages before the time even of the gigantic mammals, is preserved in the Teyler Museum at Haarlem. When the new era of the Eocene period developed modern forms of plants, their rapid growth was accompanied by a great increase in the number of insects.