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There is also a much greater fusion of the characters now belonging to distinct botanical provinces than in the Upper Miocene flora, and we shall find this fusion still more strikingly exemplified as we go back to the antecedent Eocene and Cretaceous periods.
But the remarkable fossils for which the Stonesfield slate is most celebrated are those referred to the mammiferous class. The student should be reminded that in all the rocks described in the preceding chapters as older than the Eocene, no bones of any land-quadruped, or of any cetacean, had been discovered until the Spalacotherium of the Purbeck beds came to light in 1854.
Now there is every reason to believe, on other grounds, that both Hindostan, south of the Ganges, and Africa, south of the Sahara, were separated by a wide sea from Europe and North Asia during the Middle and Upper Eocene epochs.
For a moment my gaze traversed the landscape beneath until it was caught and held by four figures near the base of the cliff a human figure held at bay by three hyaenodons, those ferocious and blood-thirsty wild dogs of the Eocene. A fourth beast lay dead or dying near by.
Nothing very strange or unlike what is now living is found in the Pleistocene the latest deposits but when we go further back strange creatures are discovered, becoming stranger and less like living things as we pass through Pliocene to Miocene, and on downwards in layers, backwards in time to the Eocene.
The same moral is inculcated by the study of every other order of Tertiary monodelphous Mammalia. Each of these orders is represented in the Miocene epoch: the Eocene formation, as I have already said, contains Cheiroptera, Insectivora, Rodentia, Ungulata, Carnivora, and Cetacea.
Then there is a blank in the record, representing the Cretaceous upheaval, and it unfortunately conceals the first great ramification of the bird world. When the light falls again on the Eocene period we find great numbers of our familiar types quite developed.
This may seem a bold assumption, but it will not appear unwarrantable to those who reflect upon the very small extent of the earth's surface which has hitherto exhibited the remains of the great Mammalian fauna of the Eocene times. In this respect, the Permian land Vertebrate fauna appears to me to be related to the Triassic much as the Eocene is to the Miocene.
Later still, in the Eocene days, though the plants of Greenland had grown slightly more temperate in type, we still find among the fossils, not only oaks, planes, vines, and walnuts, but also wellingtonias like the big trees of California, Spanish chestnuts, quaint southern salisburias, broad-leaved liquidambars, and American sassafras.
Great lakes have disappeared lofty mountains have been formed, by the reiterated emission of lava, preceded and followed by showers of sand and scoriae deep valleys have been subsequently furrowed out through masses of lacustrine and volcanic origin at a still later date, new cones have been thrown up in these valleys new lakes have been formed by the damming up of rivers and more than one assemblage of quadrupeds, birds, and plants, Eocene, Miocene, and Pliocene, have followed in succession; yet the region has preserved from first to last its geographical identity; and we can still recall to our thoughts its external condition and physical structure before these wonderful vicissitudes began, or while a part only of the whole had been completed.
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