The Ancient Life History of the Earth Part 23

Almost all the existing orders of _Birds_, if not all, are represented in the Eocene deposits by remains often very closely allied to existing types. Thus, amongst the Swimming Birds (_Natatores_) we find examples of forms allied to the living Pelicans and Mergansers; amongst the Waders (_Grallatores_) we have birds resembling the Ibis (the _Numenius gypsorum_ of the Paris basin); amongst the Running Birds (_Cursores_) we meet with the great _Gastornis Parisiensis_, which equalled the African Ostrich in height, and the still more gigantic _Dasornis Londinensis_; remains of a Partridge represent the Scratching Birds (_Rasores_); the American Eocene has yielded the bones of one of the Climbing Birds (_Scansores_), apparently referable to the Woodp.e.c.k.e.rs; the _Protornis Glarisiensis_ of the Eocene Schists of Glaris is the oldest known example of the Perching Birds (_Insessores_); and the Birds of Prey (_Raptores_) are represented by Vultures, Owls, and Hawks. The toothed Birds of the Upper Cretaceous are no longer known to exist; but Professor Owen has recently described from the London Clay the skull of a very remarkable Bird, in which there is, at any rate, an approximation to the structure of _Ichthyornis_ and _Hesperornis_. The bird in question has been named the _Odontopteryx totiapicus_, its generic t.i.tle being derived from the very remarkable characters of its jaws. In this singular form (fig. 227) the margins of both jaws are furnished with tooth-like denticulations, which differ from true teeth in being actually portions of the bony substance of the jaw itself, with which they are continuous, and which were probably encased by extensions of the h.o.r.n.y sheath of the bill. These tooth-like processes are of two sizes, the larger ones being comparable to canines; and they are all directed forwards, and have a triangular or compressed conical form. From a careful consideration of all the discovered remains of this bird, Professor Owen concludes that "_Odontopteryx_ was a warm-blooded feathered biped, with wings; and further, that it was web-footed and a fish-eater, and that in the catching of its slippery prey it was a.s.sisted by this Pterosauroid armature of its jaws." Upon the whole, _Odontopteryx_ would appear to be most nearly related to the family of the Geese (_Anserinoe_) or Ducks (_Anatidoe_); but the extension of the bony substance of the jaws into tooth-like processes is an entirely unique character, in which it stands quite alone.

[Ill.u.s.tration: Fig. 227.--Skull of _Odontopteryx toliapicus restored.

(After Owen.)]

The known _Mammals_ of the Mesozoic period, as we have seen, are all of small size; and with one not unequivocal exception, they appear to be referable to the order of the Pouched Quadrupeds (_Marsupials_), almost the lowest group of the whole cla.s.s of the Mammalia. In the Eocene rocks, on the other hand, numerous remains of Quadrupeds have been brought to light, representing most of the great Mammalian orders now in existence upon the earth, and in many cases indicating animals of very considerable dimensions. We are, in fact, in a position to a.s.sert that the majority of the great groups of Quadrupeds with which we are familiar at the present day were already in existence in the Eocene period, and that their ancient root-stocks were even in this early time separated by most of the fundamental differences of structure which distinguish their living representatives.

At the same time, there are some amongst the Eocene quadrupeds which have a "generalised" character, and which may be regarded as structural types standing midway between groups now sharply separated from one another.

The order of the _Marsupials_--including the existing Kangaroos, Wombats, Opossums, Phalangers, &c.--is poorly represented in deposits of Eocene age. The most celebrated example of this group is the _Didelphys gypsorum_ of the Gypseous beds of Montmartre, near Paris, an Opossum very nearly allied to the living Opossums of North and South America.

No member of the _Edenates_ (Sloths, Ant-eaters, and Armadillos) has. .h.i.therto been detected in any Eocene deposit. The aquatic order of the _Sirenians_ (Dugongs and Manatees), with their fish-like bodies and tails, paddle-shaped forelimbs, and wholly deficient hind-limbs, are represented in strata of this age by remains of the ancient "Sea-Cows," to which the name of _Halitherium_ has been applied. Nearly allied to the preceding is the likewise aquatic order of the Whales and Dolphins (_Cetaceans_), in which the body is also fish-like, the hind-limbs are wanting, the fore-limbs are converted into powerful "flippers" or swimming-paddles, and the terminal extremity of the body is furnished with a horizontal, tail-fin. Many existing Cetaceans (such as the Whalebone Whales) have no true teeth; but others (Dolphins, Porpoises, Sperm Whales) possess simple conical teeth. In strata of Eocene age, however, we find a singular group of Whales, const.i.tuting the genus _Zeuglodon (fig. 228), in which the teeth differed from those of all existing forms in being of two kinds,--the front ones being conical incisors, whilst the back teeth or molars have serrated triangular crowns, and are inserted in the jaw by two roots. Each molar (fig. 228, A) looks as if it were composed of two separate teeth united on one side by their crowns; and it is this peculiarity which is expressed by the generic name (Gr. _zeugle_, a yoke; _odous_, tooth). The best-known species of the genus is the _Zeuglodon cetoides_ of Owen, which attained a length of seventy feet. Remains of these gigantic Whales are very common in the "Jackson Beds" of the Southern United States. So common are they that, according to Dana, "the large vertebrae, some of them a foot and a half long and a foot in diameter, were formerly so abundant over the country, in Alabama, that they were used for making walls, or were burned to rid the fields of them."

[Ill.u.s.tration: Fig. 228.--_Zeuglodon cetoides_. A, Molar tooth of the natural size; B, Vertebra, reduced in size. From the Middle Eocene of the United States. (After Lyell.)]

The great and important order of the Hoofed Quadrupeds (_Ungulata_) is represented in the Eocene by examples of both of its two princ.i.p.al sections--namely, those with an uneven number of toes (one or three) on the foot (_Perissodactyle Ungulates_), and those with an even number of toes (two or four) to each foot (_Artiodactyle Ungulates_).

Amongst the Odd-toed Ungulates, the living family of the Tapirs (_Tapirdoe_) is represented by the genus _Coryphodon_ of Owen.

Nearly related to the preceding are the species of _Paloeotherium_, which have a historical interest as being amongst the first of the Tertiary Mammals investigated by the ill.u.s.trious Cuvier.

Several species of _Paloeothere_ are known, varying greatly in size, the smallest being little bigger than a hare, whilst the largest must have equalled a good-sized horse in its dimensions. The species of _Paloeotherium_ appear to have agreed with the existing Tapirs in possessing a lengthened and flexible nose, which formed a short proboscis or trunk (fig. 229), suitable as an instrument for stripping off the foliage of trees--the characters of the molar teeth showing them to have been strictly herbivorous in their habits. They differ, however, from the Tapirs, amongst other characters, in the fact that both the fore and the hind feet possessed three toes each; whereas in the latter there are four toes on each fore-foot, and the hind-feet alone are three-toed.

The remains of _Paloeotheria_ have been found in such abundance in certain localities as to show that these animals roamed in great herds over the fertile plains of France and the south of England during the later portion of the Eocene period. The accompanying ill.u.s.tration (fig. 229) represents the notion which the great Cuvier was induced by his researches to form as to the outward appearance of _Paloeotherium magnum_. Recent discoveries, however, have rendered it probable that this restoration is in some important respects inaccurate. Instead of being bulky, ma.s.sive, and more or less resembling the living Tapirs in form, it would rather appear that _Paloeotherium magnum_ was in reality a slender, graceful, and long-necked animal, more closely resembling in general figure a Llama, or certain of the Antelopes.

[Ill.u.s.tration: Fig. 229.--Outline of _Paloeotherium magnum_, restored. Upper Eocene, Europe. (After Cuvier.)]

The singular genus _Anchitherium_ forms a kind of transition between the _Paloeotheria_ and the true Horses (_Equidoe_). The Horse (fig. 230, D) possesses but one fully-developed toe to each foot, this being terminated by a single broad hoof, and representing the _middle_ toe--the _third_ of the typical five-fingered or five-toed limb of Quadrupeds in general. In addition, however, to this fully-developed toe, each foot in the horse carries two rudimentary toes which are concealed beneath the skin, and are known as the "splint-bones." These are respectively the _second_ and _fourth_ toes, in an aborted condition; and the first and fifth toes are wholly wanting. In _Hipparion_ (fig.

230, C), the foot is essentially like that of the modern Horses, except that the second and fourth toes no longer are mere "splint-bones," hidden beneath the skin; but have now little hoofs, and hang freely, but uselessly, by the side of the great middle toe, not being sufficiently developed to reach the ground.

In _Anchitherium_, again (fig. 230, B), the foot is three-toed, like that of _Hipparion_; but the two lateral toes (the second and fourth) are so far developed that they now reach the ground.

The _first_ digit (thumb or great toe) is still wanting; as also is the _fifth_ digit (little finger or little toe). Lastly, the Eocene rocks have yielded in North America the remains of a small Equine quadruped, to which Marsh has given the name of _Orohippus_.

In this singular form--which was not larger than a fox--the foot (fig. 230, A) carries _four_ toes, all of which are hoofed and touch the ground, but of which the _third_ toe is still the largest. The _first_ toe (thumb or great toe) is still wanting; but in this ancient representative of the Horses, the _fifth_ or "little"

toe appears for the first time. As all the above-mentioned forms succeed one another in point of time, it may be regarded as probable that we shall yet be able to point, with some certainty, to some still older example of the _Equidoe_, in which the first digit is developed, and the foot a.s.sumes its typical five-fingered condition.

[Ill.u.s.tration: Fig. 230.--Skeleton of the foot in various forms belonging to the family of the _Equidoe_. A, Foot of _Orohippus_, Eocene; B, Foot of _Anchitherium, Upper Eocene and Lower Miocene; C, Foot of _Hipparion_, Upper Miocene and Pliocene: D, Foot of Horse (_Equus_), Pliocene and Recent. The figures indicate the numbers of the digits in the typical five-fingered hand of Mammals.

(After Marsh.)]

Pa.s.sing on to the Even-toed or _Artiodactyle Ungulates_, no representative of the _Hippotamus_ seems yet to have existed, but there are several forms (_Ch.o.e.ropotamus, Hyopotamus_, &c.) more or less closely allied to the Pigs (_Suida_); and the singular group of the _Anoplotheridoe_ may be regarded as forming a kind of transition between the Swine and the Ruminants. The _Anoplotheria_ (fig. 231) were slender in form, the largest not exceeding a donkey in size, with long tails, and having the feet terminated by two hoofed toes each, sometimes with a pair of small accessory hoofs as well. The teeth exhibit the peculiarity that they are arranged in a continuous series, without any gap or interval between the molars and the canines; and the back teeth, like those of all the Ungulates, are adapted for grinding vegetable food, their crowns resembling in form those of the true Ruminants.

The genera _Dichobune_ and _Xiphodon_, of the Middle and Upper Eocene, are closely related to _Anoplotherium_, but are more slender and deer-like in form. No example of the great Ruminant group of the Ungulate Quadrupeds has as yet been detected in deposits of Eocene age.

[Ill.u.s.tration: Fig. 231.--_Anoplotherium commune_. Eocene Tertiary, France. (After Cuvier.)]

Whilst true Ruminants appear to be unknown, the Eocene strata of North America have yielded to the researches of Professor Marsh examples of an extraordinary group (_Dinocerata_), which may be considered as in some respects intermediate between the Ungulates and the Proboscideans. In _Dinoceras_ itself (fig.

232) we have a large animal, equal in dimensions to the living Elephants, which it further resembles in the structure of the ma.s.sive limbs, except that there are only four toes to each foot.

The upper jaw was devoid of front teeth, but there were two very large canine teeth, in the form of tusks directed perpendicularly downwards; and there was also a series of six small molars on each.

Each upper jaw-bone carried a bony projection, which was probably of the nature of a "horn-core," and was originally sheathed in horn. Two similar, but smaller, horn-cores are carried on the nasal bones; and two much larger projections, also probably of the nature of horn-cores, were carried upon the forehead. We may thus infer that _Dinoceras_ possessed three pairs of horns, all of which resembled the horns of the Sheep and Oxen in consisting of a central bony "core," surrounded by a h.o.r.n.y sheath. The nose was not prolonged into a proboscis or "trunk," as in the existing Elephants; and the tail was short and slender. Many forms of the _Dinocerata_ are known; but all these singular and gigantic quadrupeds appear to have been confined to the North American continent, and to be restricted to the Eocene period.

[Ill.u.s.tration: Fig. 232.--Skull of _Dinoceras mirabilis_, greatly reduced. Eocene, North America. (After Marsh.)]

The important order of the Elephants (_Proboscidea_) is also not known to have come into existence during the Eocene period. On the other hand, the great order of the Beasts of Prey (_Carnivora_) is represented in Eocene strata by several forms belonging to different types. Thus the _Ardocyon_ presents us with an Eocene Carnivore more or less closely allied to the existing Rac.o.o.ns; the _Paloeonyctis_ appears to be related to the recent Civet-cats; the genus _Hyoenodon_ is in some respects comparable to the living Hyaenas; and the _Canis Parisiensis_ of the gypsum-bearing beds of Montmartre may perhaps be allied to the Foxes.

[Ill.u.s.tration: Fig. 233.--Portion of the skeleton of _Vespertilio Parisienis_. Eocene Tertiary, France.]

The order of the Bats (_Cheiroptera_) is represented in Eocene strata of the Paris basin (Gypseous series of Montmartre) by the _Vespertilio Parisiensis_ (fig. 233), an insect-eating Bat very similar to some of the existing European forms. Lastly, the Eocene deposits have yielded more or less satisfactory evidence of the existence in Europe at this period of examples of the orders of the Gnawing Mammals (_Rodentia_), the Insect-eating Mammals (_Insectivora_), and the Monkeys (_Quadrumana_).[24]

[Footnote 24: A short list of the more important works relating to the Eocene rocks and fossils will be given after all the Tertiary deposits have been treated of.]

CHAPTER XIX.

THE MIOCENE PERIOD.

The Miocene rocks comprise those Tertiary deposits which contain less than about 35 per cent of existing species of sh.e.l.ls (_Mollusca_), and more than 5 per cent--or those deposits in which the proportion of living sh.e.l.ls is less than of extinct species. They are divisible into a _Lower Miocene_ (_Oligocene_) and an _Upper Miocene_ series.

In _Britain_, the Miocene rocks are very poorly developed, one of their leading developments being at Bovey Tracy in Devonshire, where there occur sands, clays, and beds of lignite or imperfect coal. These strata contain numerous plants, amongst which are Vines, Figs, the Cinnamon-tree, Palms, and many Conifers, especially those belonging to the genus Sequoia (the "Red-Foods"). These Bovey Tracy lignites are of Lower Miocene age, and they are lacustrine in origin. Also of Lower Miocene age are the so-called "Hempstead Beds" of Yarmouth in the Isle of Wight. These attain a thickness of less than 200 feet, and are shown by their numerous fossils to be princ.i.p.ally a true marine formation. Lastly, the Duke of Argyll, in 1851, showed that there existed at Ardtun, in the island of Mull, certain Tertiary strata containing numerous remains of plants; and these also are now regarded as belonging to the Lower Miocene.

In _France_, the Lower Miocene is represented in Auvergne, Cantal, and Velay, by a great thickness of nearly horizontal strata of sands, sandstone, clays, marls, and limestones, the whole of fresh-water origin. The princ.i.p.al fossils of these lacustrine deposits are _Mammalia_, of which the remains occur in great abundance. In the valley of the Loire occur the typical European deposits of Upper Miocene age. These are known as the "Faluns,"

from a provincial term applied to sh.e.l.ly sands, employed to spread upon soils which are deficient in lime; and the Upper Miocene is hence sometimes spoken of as the "Falunian" formation. The Faluns occur in scattered patches, which are rarely more than 50 feet in thickness, and consist of sands and marls. The fossils are chiefly marine; but there occur also land and fresh-water sh.e.l.ls, together with the remains of numerous Mammals. About 25 per cent of the sh.e.l.ls of the Faluns are identical with existing species. The sands, limestones, and marls of the Department of Gers, near the base of the Pyrenees, rendered famous by the number or Mammalian remains exhumed from them by M. Lartet, also belong to the age of the Faluns.

In _Switzerland_, between the Alps and the Jura, there occurs a great series of Miocene deposits, known collectively as the "Mola.s.se," from the soft nature of a greenish sandstone, which const.i.tutes one of its chief members. It attains a thickness of many thousands of feet, and rises into lofty mountains, some of which--as the Rigi--are more than 6000 feet in height. The middle portion of the Mola.s.se is of marine origin, and is shown by its fossils to be of the age of the Faluns; but the lower and upper portions of the formation are mainly or entirely of fresh-water origin. The Lower Mola.s.se (of Lower Miocene age) has yielded about 500 species of plants, mostly of tropical or sub-tropical forms. The Upper Mola.s.se has yielded about the same number of plants, with about 900 species of Insects, such as wood-eating Beetles Water-beetles, White Ants, Dragon-flies, &c.

In _Belgium_, strata of both Lower and Upper Miocene age are known,--the former (_Rupelian Clays_) containing numerous marine fossils; whilst the latter (_Bolderberg Sands_) have yielded numerous sh.e.l.ls corresponding with those of the Faluns.

In _Austria_, Miocene strata are largely developed, marine beds belonging to both the Lower and Upper division of the formation occurring extensively in the Vienna basin. The well-known Brown Coals of Radaboj, in Croatia, with numerous plants and insects, are also of Lower Miocene age.

In _Germany_, deposits belonging to both the Lower and Upper division of the Miocene formation are extensively developed.

To the former belong the marine strata of the Mayence basin, and the marine _Rupelian Clay_ near Berlin; whilst a celebrated group of strata belonging to the Upper Miocene occurs near Epplesheim, in Hesse-Darmstadt, and is well known for the number of its Mammalian remains.

In _Greece_, at Pikerme, near Athens, there occurs a celebrated deposit of Upper Miocene age, well known to palaeontologists through the researches of M. M. Wagner, Roth, and Gaudry upon the numerous Mammalia which it contains. In _Italy_, also, strata of both Lower and Upper Miocene age are well developed in the neighbourhood of Turin.

In the _Siwalik Hills_, in India, at the southern foot of the Himalayas, occurs a series of Upper Miocene strata, which have become widely celebrated through the researches of Dr Falconer and Sir Proby Cautley upon the numerous remains of Mammals and Reptiles which they contain. Beds of corresponding age, with similar fossils, are known to occur in the island of Perim in the Gulf of Cambay.

Lastly, Miocene deposits are found in _North America_, in New Jersey, Maryland, Virginia, Missouri, California, Oregon, &c., attaining a thickness of 1500 feet or more. They consist princ.i.p.ally of clays, sands, and sandstones, sometimes of marine and sometimes of fresh-water origin. Near Richmond, in Virginia, there occurs a remarkable stratum, wrongly called "Infusorial Earth," which is occasionally 30 feet in thickness, and consists almost wholly of the siliceous envelopes of certain low forms of plants (Diatoms), along with the spicules of Sponges and other siliceous organisms (see fig. 16). The _White River Group_ of Hayden occurs in the Upper Missouri region, and is largely exposed over the barren and desolate district known as the "Mauvaises Terres." They have a thickness of 1000 feet or more, and contain numerous remains of Mammals. They are of lacustrine origin, and are believed to be of the age of the Lower Miocene. Upon the whole, about from 15 to 30 per cent of the _Mollusca_ of the American Miocene are identical with existing species.

In addition to the regions previously enumerated, Miocene strata are known to be developed in _Greenland, Iceland, Spitzbergen_, and in other areas of less importance.

The _life_ of the Miocene period is extremely abundant, and, from the nature of the deposits of this age, also extremely varied in its character. The marine beds of the formation have yielded numerous remains of both Vertebrate and Invertebrate sea-animals; whilst the fresh-water deposits contain the skeletons of such sh.e.l.ls, fishes, &c., as now inhabit rivers or lakes. Both the marine and the lacustrine beds have been shown to contain an enormous number of plants, the latter more particularly; whilst the Brown Coals of the formation are made up of vegetable matter little altered from its original condition. The remains of air-breathing animals, such as Insects, Reptiles, Birds, and Mammals, are also abundantly found, more especially in the fresh-water beds.

The _plants_ of the Miocene period are extraordinarily numerous, and only some of the general features of the vegetation of this epoch can be indicated here. Our chief sources of information as to the Miocene plants are the Brown Coals of Germany and Austria, the Lower and Upper Mola.s.se of Switzerland, and the Miocene strata of the Arctic regions. The lignites of Austria have yielded very numerous plants, chiefly of a tropical character--one of the most noticeable forms being a Palm of the genus _Sabal_ (fig.

234, B), now found in America. The plants of the Lower Miocene of Switzerland are also mostly of a tropical character, but include several forms now found in North America, such as a Tulip-tree (_Liriodendron_) and a Cypress (_Taxodium_). Amongst the more remarkable forms from these beds may be mentioned Fan-Palms (_Chamoerops_, fig 234, A), numerous tropical ferns, and two species of Cinnamon. The plant-remains of the Upper Mola.s.se of Switzerland indicate an extraordinarily rank and luxuriant vegetation, composed mainly of plants which now live in warm countries. Among the commoner plants of this formation may be enumerated many species of Maple (_Acer_), Plane-trees (_Plata.n.u.s_ fig. 235), Cinnamon-trees (fig. 236), and other members of the _Lauraceoe_, many species of _Proteaccoe_ (_Banksia, Grevillea_, &c.), several species of Sarsaparilla (_Smilax_), Palms, Cypresses, &c.

[Ill.u.s.tration: Fig. 234.--Miocene Palms A, _Chamoerops Helvetica_; B, _Sabal major_. Lower Miocene of Switzerland and France.]

[Ill.u.s.tration: Fig. 235.--_Plata.n.u.s aceroides_, an Upper Miocene Plane-tree. a, Leaf; b, The core of a bundle of fruits; c, A single fruit.]

[Ill.u.s.tration: Fig. 236.--_Cinnamomum polymorphum_. a, Leaf; b, Flower. Upper Miocene.]

In Britain, the Lower Miocene strata of Bovey Tracy have yielded remains of Ferns, Vines, Fig, Cinnamon, _Proteaccoe_, &c., along with numerous Conifers. The most abundant of these last is a gigantic pine--the _Sequoia Couttsioe_--which is very nearly allied to the huge _Sequoia_ (_Wellingtonia_) _gigantea_ of California. A nearly-allied form (_Sequoia Langsdorffi_) has been detected in the leaf-bed of Ardtun, in the Hebrides.

In Greenland, as well as in other parts of the Arctic regions, Miocene strata have been discovered which have yielded a great number of plants, many of which are identical with species found in the European Miocene. Amongst these plants are found many trees, such as Conifers, Beeches, Oaks, Maples, Plane-trees, Walnuts, Magnolias, &c., with numerous shrubs, ferns, and other smaller plants. With regard to the Miocene flora of the Arctic regions, Sir Charles Lyell remarks that "more than thirty species of Coniferae have been found, including several Sequoias (allied to the gigantic Wellingtonia of California), with species of _Thujopsis_ and _Salisburia_, now peculiar to j.a.pan. There are also beeches, oaks, planes, poplars, maples, walnuts, limes, and even a magnolia, two cones of which have recently been obtained, proving that this splendid evergreen not only lived but ripened its fruit within the Arctic circle. Many of the limes, planes, and oaks were large-leaved species; and both flowers and fruits, besides immense quant.i.ties of leaves, are in many cases preserved.

Among the shrubs are many evergreens, as _Andromeda_, and two extinct genera, _Daphnogene_ and _M'Clintockia_, with fine leathery leaves, together with hazel, blackthorn, holly, logwood, and hawthorn. A species of Zamia (_Zimites_) grew in the swamps, with _Potamogeton, Sparganium_, and _Menyanthes_; while ivy and villes twined around the forest-trees, and broad-leaved ferns grew beneath their shade. Even in Spitzbergen, as far north as lat. 78 56', no less than ninety-five species of fossil plants have been obtained, including _Taxodium_ of two species, hazel, poplar, alder, beech, plane-tree, and lime. Such a vigorous growth of trees within 12 of the pole, where now a dwarf willow and a few herbaceous plants form the only vegetation, and where the ground is covered with almost perpetual snow and ice, is truly remarkable."

Taking the Miocene flora as a whole, Dr Heer concludes from his study of about 3000 plants contained in the European Miocene alone, that the Miocene plants indicate tropical or sub-tropical conditions, but that there is a striking inter-mixture of forms which are at present found in countries widely removed from one another. It is impossible to state with certainty how many of the Miocene plants belong to existing species, but it appears that the larger number are extinct. According to Heer, the American types of plants are most largely represented in the Miocene flora, next those of Europe and Asia, next those of Africa, and lastly those of Australia. Upon the whole, however, the Miocene flora of Europe is mostly nearly allied to the plants which we now find inhabiting the warmer parts of the United States; and this has led to the suggestion that in Miocene times the Atlantic Ocean was dry land, and that a migration of American plants to Europe was thus permitted. This view is borne out by the fact that the Miocene plants of Europe are most nearly allied to the living plants of the eastern or Atlantic seaboard of the United States, and also by the occurrence of a rich Miocene flora in Greenland. As regards Greenland, Dr Heer has determined that the Miocene plants indicate a temperate climate in that country, with a mean annual temperature at least 30 warmer than it is at present.