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In these the scheme of life, as now known to us, was incomplete—either some great order being largely predominant, or one or more orders altogether wanting. Taking the fauna alone, the Laurentian, Cambrian, and Silurian were characterised by the general absence of vertebrata; in the Old Eed Sandstone we had no reptiles, nor birds, nor mammals; in the Coal, no birds nor mammals; and in the secondary ages, nothing apparently higher than marsupials. But now, and for the first time in the history of the earth, we are presented with all the great orders of plants and animals, and were it not for certain forms that have become extinct and others that are peculiar to the current epoch, we could almost fancy we were dealing with the botany and zoology of the present day. So far as they have been critically examined, the plants of the lower European tertiaries indicate a much warmer climate than now prevails over the same latitudes; and this higher temperature was in all likelihood brought about by the peculiar disposition of the sea and land. Broad rivers flowing from tropical latitudes, and inland seas extending longitudinally into sub-tropical or even tropical zones, would be sufficient to account for the presence of palms and other allied vegetation in the lignites of Europe; and what we already know of the boundaries of the lower tertiaries, affords the best reason for believing that such were the great geographical arrangements of the period. In our reasonings on former climates we are too apt to look to mere zones of latitude, without sufficiently' allowing for disposition and altitude of land, the trend of oceanic currents, the prevailing set of winds, the effects of atmospheric humidity, and other similar incidents by which the luxuriance or sterility of life is often more immediately affected than by mere propinquity to the equator. During the deposition of the middle and upper tertiaries the climate seems to have gradually declined, and the European lignites of these periods exhibit a flora bearing a striking resemblance to that which now flourishes in North America. We say "European lignites," for the lignites of Eastern Asia, of New Zealand, and of British America, seem each to be characterised by its own peculiar plants, and these for the most part having a general relationship to the existing vegetation of the same regions; It must be admitted, however, that the flora of all the tertiaries—lower, middle, and upper—requires much more minute botanical investigation; and till this is done, geologists can offer little more than mere approximations to the conditions of the period.
Like the flora, the fauna of the lower tertiaries would seem to imply the existence of genial conditions at once of climate, food, and habitat. Gigantic sharks, turtles, crocodiles, and sea-serpents in the basins of London, Paris, and the Ehine, indicate much warmer waters than these latitudes now enjoy; while elephantine, tapir-like, camel-like, lion-like, and ape-like forms among their terrestrial fauna, point unmistakably to sub-tropical or tropical surroundings. Nor is it mere variety of generic and specific forms among these mammalia, but their huge size and vast numerical abundance, that point in the same manner to favourable conditions of existence. Indeed one of the most remarkable features in the life of the period is the vast bulk of the mammalia as compared with the same orders still existing. This massiveness of structure runs throughout all the divisions of the system—lower, middle, and upper—and marks alike the tertiary fauna of Europe, Asia, America, and Australia. If the number and magnitude of reptilian forms that thronged the secondary waters have conferred on that cycle the designation of "The Age of Eeptiles," the number and magnitude of mammalian forms that peopled the tertiary lands may in like manner entitle this period to be signalised as " The Age of Mammals." Palmotheres, or tapir-like beasts, huge as elephants; hippotheres, or horse-like animals of massive form and structure; sivatheres, or antelope-forms, tall as giraffes; megatheres, or sloths, weightier than the weightiest hippopotamus; glyptodons, or armadilloes, that could enclose a score of the living species under their shields; macrauchenes, or llama-forms, bulky as camels; hycenodons, or hyaenas, stronger than tigers; diprotodons, or kangaroos, heavier than oxen; and colossocheles, or carapaced turtles, full fourteen feet in diameter, are but random instances of the colossal structures that have been exhumed from the sediments of the tertiary epoch. In this respect the fauna of the period seems to corroborate the idea that there is a culminating point in the life of orders, as there is in the life of individuals—a period when they attain their maximum development in numbers, variety, and magnitude, and after which they gradually decline and disappear, to make way for some newer and advancing order. Or as it has been put by one of the most recent writers on systematic geology (Professor Haughton), "it appears to be an almost universal law of life on the globe, that each group of organic beings increased in size and in importance in an uninterrupted line from the commencement of its existence, until its members reached their maximum in some short time—I mean, short as compared with their whole life-history—after their original creation and appearance upon the globe; and it would almost seem as if, having reached that maximum of development, they then commenced a process of degeneracy and decline."
Another remarkable feature in the tertiary fauna is the prevalence of what are styled "intermediate forms," that is, of creatures partaking of the characteristics of two or more adjacent orders—a sort of interfusion, as it were, of families and genera, which now stand distinct and separate. We have thus elephant-like tapirs, camel-like stags, giraffelike camels, horse-like antelopes, lion-like bears, tiger-like hyaenas, and. numerous other inosculating forms, which, had they existed now, would have filled up more closely the meshes of the great network of existence. Nor is it among the mammalia alone that this gigantic size and peculiarity of form make their appearance; for birds, reptiles, and fishes partake of similar characteristics, and point to the same favourable conditions of growth, and to the same great law of structural relationship and development. We say structural relationship, for, as has been well remarked by Professor Jukes, "in speaking of these extinct animals as forming links between our existing forms, we must never forget that the living forms are not the types, but the variations from the types. We are apt to assume that the forms with which we are most familiar are the most simple and natural; but the scientific naturalist often finds some extinct form as the simple archetype, from which numerous others have departed more and more by variation and combination of parts in subsequent periods." We are right when we speak of these tertiary mammals as holding an intermediate place between some existing forms, but we are wrong if we consider them on that account to be either more complex in structure or varied in function. "A three-toed horse (hippotherium) would now be looked upon says Mr Woodward, "as a lusus natural; but in truth, the ordinary one-toed horse of the present day is by far more wonderful."
We have already remarked, that though the distribution of the tertiary seas and lands differed considerably from the present, there must still have been a certain approximation to the present arrangement, inasmuch as the tertiary flora and fauna of every region, and especially of the later tertiaries, bear a considerable resemblance to the plants and
animals that yet flourish theTe. There may be local differences among the tertiary basins of Europe and Asia • but still throughout the whole there is, if we may so phrase it, an aspect of Old World forms. The species and genera may differ, and there may be forms that stand intermediate between two or three conterminous families; yet, on the whole, we see in the mastodons and mammoths, the pakeotheres and anoplotheres, the hyopotami and chaeropotami, the sivatheres and merycotheres, the machairodons and hyaenodons, the prototypes and forerunners of the elephants, rhinoceroses, hippopotami, river-hogs, antelopes, giraffes, camels, horses, oxen, lions, tigers, and hyaenas, that now inhabit the eastern hemisphere. In like manner the megatheres, mylodons, glyptodons, and macrauchenes of South America, were the gigantic forerunners of the sloths, armadilloes, and llamas that now people that continent; while the diprotodons, zygomatures, and nototheres of Australia, foreshadow the kangaroos and wombats so exclusively characteristic of that peculiar sub-continent.* Everything, indeed, both in flora and fauna, indicates the approach of existing nature; but this, as in all other cosmical operations, by slow and gradual steps—the eocene, miocene, and pliocene, each having its own special phases, and these diverging from those of the current epoch according to their relative distances in time.
What a picturesque and luxuriant scene these grassy plains and glades and river-banks of the old tertiary times must have presented! Uplands fretted with scrub, lagoons and river-creeks fringed with palms and tropical forest-growths, and swampy deltas teeming with tangling
* By a perusal of the illustrations in any work on Palaeontology, such as Owen's * Fossil Mammals/ the non-scientific reader will be enabled to trace the resemblance between these extinct forms and the existing fauna far more readily than by any amount of verbal description.