A Jurassic Bird
Fig. 148.—A Jurassic Bird (Archæopteryx macroura).—After Owen.
Jaw of a Cretaceous Toothed Bird
Fig. 149.—Jaw of a Cretaceous Toothed Bird (Ichthyornis dispar).—After Marsh. Natural size.
The approximation of the winged reptiles to the birds is further increased by the facts that in the Jurassic and Cretaceous periods there were birds having reptilian tails and probably toothed jaws (Archæopteryx macroura,Fig. 148). The species just named, while in its limbs, trunk, and feathers a veritable perching bird, resembles a reptile in its head and tail. In the Cretaceous of Western America, Marsh has recently discovered two distinct types of toothed birds, one having the teeth in regular sockets, the other having them implanted in a groove in the jaw. One of these birds (Ichthyornis dispar,Fig. 149) was larger than a pigeon, with powerful wings constructed like those of ordinary birds. It had also the curious and old-fashioned peculiarity of biconcave vertebræ, like those of fishes and some reptiles. Another (Hesperornis regalis) stood five or six feet high, and had rudimentary wings like those of the Penguins. These toothed birds extend into the Eocene Tertiary, where theOdontopteryxof Owen has been known for some time. In the Eocene, however, this toothed bird is associated with others of ordinary types, allied closely to the Ostriches, the Pelicans, the Ibis, the Woodpeckers, the Hawks, the Owls, the Vultures, and the ordinary perching birds. In the Later Mesozoic, indeed, some reptiles became so bird-like that they nearly approached the earliest birds; but this was a final and futile effort of the reptile to obtain in the air that supremacy which it had longenjoyed in earth and water; and its failure was immediately succeeded in the Eocene by the appearance of a cloud of true birds, representing all the existing orders of the class.
Jaw of Bathygnathus borealis (Leidy).
Fig. 150.—Jaw ofBathygnathus borealis(Leidy). A Triassic Dinosaur from Prince Edward Island.
a, Cross section of second tooth, natural size.b, Fifth tooth, natural size.
We may close our notice of the winged reptiles of the Mesozoic by quoting from Phillips his summary of the characters ofRhamphorhyncus(Fig. 147)67: “Gifted with ample means of flight, able at least to perch on rocks and scuffle along the shore, perhaps competent to dive, though not so well as a palmiped bird, many fishes must have yielded to the cruel beak and sharp teeth of theRhamphorhyncus. If we ask to which of the many families of birds the analogy of structure and probable way of life would lead us to assimilate Rhamphorhyncus, the answer must point to the swimming races, with long wings, clawed feet, hooked beak, and habits of violence and voracity; and for preference, the shortness of the legs and other circumstances may be held to claim for the Stonesfield fossil a more than fanciful similitude to the groups of Cormorants and other marine divers which constitute an effective part of the picturesque army of robbers of the sea.”
Hadrosaurus Foulkii.
Fig. 151.—Hadrosaurus Foulkii(Cope). An Herbivorous Dinosaur, 28 feet long.—After Hawkins’s restoration.
Lastly, the reptiles, in this age of their imperial sway, culminated in theDinosaurians, animals far above any modern Reptilia in the perfection of their organisation, and many of them of gigantic size. Just as the Pterosaurs filled the place now occupied by the birds, so the Dinosaurs filled that represented by the mammals, or rather they took up a place holding some close relations with both the birds and the mammals. There were thus reptilian animals which on the one hand were the elephants and lions of their time, and on the other bore a grotesque resemblance to creatures so unlike these as the Ostriches, in so far as their anatomical structure was concerned; while it is evident that their whole organisation places them in the highest position possible within the reptilian class. Someof them must have been herbivorous, and probably slow in movement and quiet in nature. Others were carnivorous and of terrible energy, while furnished with the most destructive weapons (Figs. 152, 153). Many had the power of erecting themselves on their hind-feet and walking as bipeds; and to adapt them to this end their hinder limbs were very large and strong, and they had long pillar-like tails, while their fore-feet were comparatively small, and used perhaps mainly for prehension (Figs. 151, 154).
Jaws of Megalosaurus.
Fig. 152.—Jaws ofMegalosaurus.—After Phillips. One-tenth natural size.
The size of some of these creatures was stupendous. TheHadrosaurusof New Jersey, an Herbivorous species (Fig. 151), when erected on its hind limbs and tail, must have stood more than twenty feet in height.MegalosaurusandIguanodon, of the English Jurassic and Wealden, must have been of still more gigantic size. The former was a carnivorous animal, its head (Fig. 152) four or five feet in length, armed with teeth, sabre-shaped, sharp and crenate on the edges (Fig. 153), its hind limbs of enormous power, so that if our imagination does not fail us in the attempt to realise such a wonder, we may evensuppose this huge animal, much larger than the largest elephant, springing like a tiger on its prey, a miracle of terrible strength and ferocity, before which no living thing could stand. Its companion,Iguanodon, was, on the contrary, a harmless herbivorous creature, using its great strength and stature as a means of obtaining leaves and fruits for food, and perhaps falling a prey to the larger Carnivorous Dinosaurs its contemporaries. A still more bulky animal was theCeteosaurus, so admirably described by Phillips. Its thigh-bone measures more than five feet in length and a foot in diameter; and it must have stood ten feet high when on all fours, while its length must have reached forty or fifty feet. It seems from the forms of its bones to have been able to walk on land, but probably spent most of its time in the water, where it may be compared to a huge reptilian hippopotamus. Very recently some bones found in rocks, possibly of Wealden age, inWestern America, and described by Cope and by Marsh, indicate that evenCeteosaurushad not attained to the maximum of Dinosaurian dimensions. These new animals have vertebræ twenty inches in length and from twelve inches to thirteen inches in the diameter of their bodies, while their lateral processes stretched three and a half feet. The shoulder-blade of one species is five feet in length, and its thigh-bone is six feet long. From these measurements Cope concludes that, unlike most other Dinosaurs, it had the fore-feet larger in proportion than the hind-feet, so as to have somewhat the appearance of a large giraffe. The bones of the back have a remarkable cavernous structure, which Cope interprets as indicating air cavities, to give lightness, as in the case of the bones of birds; but Owen suggests that the cavities were filled with cartilage, and that the animals were aquatic in their habits. Evidently in point of size the Dinosaurs had a better claim than even Behemoth to be called the “chief of the ways of God.” Some of them, however, were of small size, and probably active and bird-like in their movements. One of these is the animal represented inFig. 154, a species from the lithographic limestone of Solenhofen.68
Tooth of Megalosaurus.
Fig. 153.—Tooth ofMegalosaurus. Natural size.
a, Cross section.b, Crenellation of edges. Enlarged.
Nothing in the life of the Mesozoic has so seized on the imagination of evolutionists as the links of connection between birds and reptiles, which has even been introduced by Huxley into the classification of animals, by his grouping these heretofore very distinct classes in one gigantic and comprehensive class ofSauropsida. It is necessary, therefore, to glance at these connections, and if possible to arrive at some conception of their true value. The links which connect the reptiles and the birds are twofold. First, that between the Dinosaurs and the ostrich tribe,69and, secondly, that between the Pterodactyls andtheir allies, and the peculiar Mesozoic birds, such asArchæopteryx. The first would serve to account for the few exceptional Struthious birds of the modern world. The second would account for the Passerine and other more ordinary birds; and thus, according to evolution, the now somewhat homogeneous class of birds would have a double, or more probably multiple, origin from several lines of reptilian ancestors. This, no doubt, greatly complicates the links of connection, whether these be supposed to indicate derivation or not.
Compsognathus.
Fig. 154.—Compsognathus.One of the smaller Dinosaurs.—After Wagner.
If we inquire as to the first connection above stated, we may define it briefly in the words of Prof. Phillips, with reference toMegalosaurus, which “was not a ground-crawler, like the alligator, but moving with free steps, chiefly, if not solely, on the hind limbs, and claiming a curious analogy, if not some degree of affinity, with the ostrich.”70But thequestion arises, Was this resemblance merely that of two oviparous bipeds, or anything more? and when we set off, against the resemblance in haunch bones and hind limbs, the entire dissimilarity in head, in fore limbs, in vertebræ, in tail, and probably in external covering, we are disposed to agree with Huxley in his statement, with respect to the Struthious birds, that their “total amount of approximation to the reptilian type is but small; and the gap between reptiles and birds is but very slightly narrowed by their existence.” There is therefore here a great gap, even in the linking together of the types, independently of any question of derivation.
The second line of connection appears at first sight more promising.Archæopteryxhas a reptilian tail, and claws on the wing; and, as it had toothed jaws, like some of the birds in the Cretaceous, must have altogether made a much nearer approach to a reptile than any modern bird does. The remarkable “fish-bird” (Ichthyornis) of Marsh is also very reptilian in some of its characters. But when we compare these reptilian birds with the Pterodactyls and their allies, a vast gap at once becomes apparent. Disregarding the external clothing, we find the wing in the two groups entirely dissimilar in details of construction, and this dissimilarity extends to the hind limbs as well, so that the Pterodactyls resemble bats rather than birds.
Without committing ourselves to any doctrine of development, we might have rejoiced if our geological discoveries had established a continuous chain, or two continuous chains, of being between the reptiles and the birds; but this end is evidently still far from being attained, though some approximation has undoubtedly been made. To quote again the admission of Huxley: “Birds are no more modified reptiles than reptiles are modified birds, the reptilian and ornithic types being both in reality somewhat different superstructures, raised upon one and the same ground-plan”—that ground-plan being the idea of the air-breathing oviparous vertebrate, and the reptilerepresenting the less specialized and less ornate building. As yet the origin of that idea, and the mode of carrying it out to completion, remain unknown, except to the Architect and Builder, who may reveal them to earnest seekers for truth in His own good time.
As to links of connection with the Mammalia, these are still more obscure. In the Mesozoic the mammals are represented as yet only by a few small species allied to the pouched (Marsupial) and insectivorous quadrupeds of Australia, and these are closely linked with some of the smaller carnivorous Mammalia of the early Tertiary; but neither approach very closely to any known reptilian types. Nor have we yet any connecting links between the great marine reptiles and the Cetaceans and Sirenians which in the Tertiary take their place in the sea.
It is an interesting fact, to come before us in our next chapter, that the great land reptiles of the Mesozoic survived long enough to become contemporary with the introduction and first luxuriance of the modern types of vegetation in the later Cretaceous. It would be natural to suppose that access to these great supplies of better food would have stimulated the increase and development of the herbivorous species, and would have indirectly had the same effect on those that were carnivorous; but the opposite result seems to have followed, and in the next period the reptiles altogether gave place to the mammals, unless, indeed, they were themselves by some mysterious and comparatively rapid process transformed into Mammalia, to suit them to the better conditions of an improved world.
So far as yet known, the reign of reptiles was world-wide in its time; and the imagination is taxed to conceive of a state of things in which the seas swarmed with great reptiles on every coast, when the land was trodden by colossal reptilian bipeds and quadrupeds, in comparison with some of which our elephants are pygmies, and when the air was filled with the grotesque and formidable Pterodactyls. Yet this is no fancypicture. It represents a time which actually existed, when that comparatively low, brutal, and insensate type of existence represented by the modern crocodiles and alligators was supreme in the world. The duration of these creatures was long, and in watching the progress of creation, they would have seemed the permanent inhabitants of the earth. Yet all have perished, and their modern successors, except a few large species existing in the warmer climates, have become subject to the more recently introduced Mammalia.
How did the ancient reptile aristocracy perish? We are ignorant of the details of the catastrophe, but their final disappearance and replacement by the more modern fauna was connected with a great continental subsidence in the Cretaceous age, and with changes of climate and conditions preceding and subsequent to it. Yet the struggle for continued dominion was hard and protracted; and toward its close some of the champions of the reign of reptiles were the greatest and most magnificent examples of the type; as if they had risen in their might to defy approaching ruin. Thus some of the most stupendous forms appear in the later Cretaceous, after the great subsidence had made progress and almost attained its consummation. Like the antediluvian giants, they were undismayed even when the land began to sink beneath their feet; and for them there was no ark of deliverance.
Lower Cretaceous Leaves.
Lower Cretaceous Leaves. Reduced in size.—After Lesquereux.
a,Aralia Saporteana.b,Sassafras araliopsis.c,Quercus primordialis.d,Fagus polyclada.e,Salix proteæfolia.f,Laurus proteæfolia.
Fora long time it was believed by geologists that a great and mysterious gap separated the Upper Cretaceous from the oldest Tertiary formations; and in Western Europe, in so far as physical conditions and animal life are concerned, the severance seemed nearly complete. Oceanic deposits, like the Upper Chalk, are succeeded by beds of littoral and estuarine characters. The last and some of the greatest of the Mesozoic Saurians have their burial-places in the Upper Cretaceous, and appear no more on earth. The wonderful shell-fishes of the Ammonite group, and the cuttle-fishes of the Belemnite type, share the same fate. With the earliest deposits of the Eocene Tertiary came in multitudes of large Mammalia heretofore unknown, and the Cetaceans appear in the sea instead of the great marine lizards; while shells, corals, and crustaceans of modern types swarm in the waters. Thus it is true that a great and apparently somewhat abrupt change takes place at the close of the Cretaceous, and terminates for ever the reptilian age. Even in regions like Western America, where physically the later Cretaceous shades gradually into the earlier Tertiary, so that there have been doubts as to the limits of these several periods, the same great change in animal life occurs.
But a link of connection has at length been found in the history of the vegetable kingdom. The modern flora camein with its full force in the later Cretaceous, before the end of the reptilian age, and continued onward to the present time. Thus the plant takes precedence of the animal, and the preparation was made for the mammalian life of the Eocene by the introduction of the modern flora in the Cretaceous period. In like manner it is possible that the great graphite deposits of the Laurentian indicate a vegetation which preceded the swarming marine life of the Cambrian; and it is not improbable that the Palæozoic land flora existed long before the first land animals. Thus the plant, as in the old Mosaic record, ever appears on the day before the animal, in each stage of the development of the world.
In ChapterIV.we traced the history of the old and rich vegetation of the Coal period. But this vegetation consisted principally of cryptogams and those lowest phænogams, of the pine and cycad groups, which have naked seeds. In the modern flora we may arrange the several groups of plants, somewhat naturally, as follows:—
With reference to the history of these groups the record stands as follows:—In the Palæozoic age classes 3 and 4 culminated, and constituted the great mass of the arboreal vegetation. On entering the Mesozoic, No. 3becomes somewhat diminished, but No. 4 continues with unabated prevalence, so that the Mesozoic has sometimes been characterized as emphatically the age of Gymnosperms. With these appear some Endogens, allied to the modern Yuccas and Screw pines and Arums. But in the lower Mesozoic rocks we have no representatives of the broad-leaved Exogens (Angiosperms), which constitute the great mass of ordinary forest vegetation; and it is only in the Cretaceous that we find them appearing in force, and that the monotonous vegetation of the older style was replaced by the more beautiful and varied forms of our modern woods.
In Europe, in the lower part of the Upper Cretaceous of Bohemia (Cenomanian), have been found some leaves which indicate the beginning of this change. These have been referred to Cæsalpinias or Brasilettos, pod-bearing trees of India and tropical America, Aralias or Ginsengs, Magnolias, Laurels, an Ivy, and a peculiar and uncertain genus (Credneria). With these are noble palms, both of the types with pinnate and palmate leaves, and trees allied to the Giant Sequoias of California, and to the Araucarian pines of the southern hemisphere. (See Frontispiece to this Chapter.) These ancient Cretaceous forests of Eastern Europe are compared by Saporta with those which now live in the warmer portions of China or in South America—truly a marvellous change from the sombre and uniform vegetation by which they seem to have been immediately preceded. A still further development of modern vegetation takes place in the next or highest member of the Cretaceous, the Maestricht beds (Senonian), where we find a crowd of modern types. On this great change Count Saporta remarks with truth that there seem to have been periods of pause and of activity in the introduction of plants. The Jurassic period was one of inactivity; and a new and vigorous evolution, as he regards it, is introduced in the middle of the Cretaceous.
This new and grand elevation of the vegetable kingdom inthe Cretaceous age was not local merely. In Moravia, in the Hartz, in Belgium and France, even in Greenland, the same great renewing of the face of the earth was in progress. In America it was proceeding on a grand scale, and seems to have set in earlier than in Europe.71In the Dakota group of the West, one of the lower members of the Cretaceous, and covering a vast area, a rich angiospermous flora has been discovered by Hayden, and described by Lesquereux and Newberry, and beds of coal have been formed from its remains. In Vancouver’s Island in British Columbia, Cretaceous coal measures occur, comparable in value and in the excellence of the fuel they afford with those of the true coal formation. Some of the beds of coal are eight feet in thickness, and the shales associated with them abound in leaves of exogenous trees generally similar to those still living in America. In these beds are also found mineralized trunks, which present under the microscope the familiar structures of our oaks, birches, and other modern trees. Thus all over the northern hemisphere the elevation of the land out of the waters of the great Cretaceous subsidence was signalized by a development of noble and exuberant forest vegetation, of the types still extant. The following list of families found in the Cretaceous, after Saporta, will show the botanist how fully our modern Exogens are represented:—
Of the plants in this list, some, like the oaks, birches, willows, and heaths, are common and familiar members of the flora of the northern hemisphere to-day, and even of the European flora. Some, like the Magnolias, Myricas, and witch-hazels, are characteristically American, and a few, like the Proteaceæ, are now confined to the southern hemisphere. Some of these families have dwindled since the Cretaceous time, so as to be represented by very few species, or at least have not advanced, while others have multiplied and prospered; and on the whole the flora of the northern hemisphere seems to have been as rich in this early beginning of our modern forests as it is at the present day. Lesquereux’s results, with reference to the American flora of the Dakota group, are very similar, and present some surprising features of resemblance to modern American forests, though he remarks that these Cretaceous trees are generally characterized by the even or unserrated edges of their leaves; and the same remark seems to apply to the oldest Cretaceous leaves of Europe.
A very singular feature of the Cretaceous flora is the number of species of some genera now represented by few or even a single species; and this is the more remarkable when we consider how few species, comparatively, of the older flora, are known to us. For example, Lesquereux, though aware of the great variability of the modern Sassafras of America, recognizes eight species of this genus in the Dakota Cretaceous, one of which seems to be that still living in America, so that it has continued unchanged, while the others have perished (Fig. 155). Thus this genus culminates at once in the Cretaceous, but continues still in one of its species. Again, the tulip-tree,Liriodendron, one of the most beautiful, unique, and invariable of American trees, is represented by one sole species in the present world. There seem to be no less than four in the Dakota beds, besides others in the Cretaceous of New Jersey, and one species is found in the Tertiary of Greenland as well as in that of Europe (Fig. 156). There areprobably four or five species of plane-tree (Platanus) now extant, of which but one occurs in America, unlessP. Mexicana, the Mexican plane-tree, is a good species as distinct from the ordinary, more northern, form. There are seven species, according to Lesquereux, in the Cretaceous of Dakota alone. This sort of evolution backward, or from many species to few, would probably be greatly increased, had we fuller knowledge of the Cretaceous flora, as there are several genera already represented by as many species as they can boast in modern times. We have already seen that this abrupt and sudden culmination of genera and families, and their subsequent decadence, is no rare thing in geology, and it connects itself with that idea of periods of creative activity which we have already had occasion to notice.
Sassafras cretaceum.
Fig. 155.—Sassafras cretaceum(Newberry).
A Cretaceous Tulip-tree.
Fig. 156.—Liriodendron primævum(Newberry). A Cretaceous Tulip-tree.
Onoclea sensibilis.
Fig. 157.—Onoclea sensibilis.Eocene.—After Newberry.
Davallia tenuifolia.
Fig. 158.—Davallia tenuifolia.Eocene.—After Dawson. Natural size and enlarged.
I have dwelt principally on the phænogamous plants of the Cretaceous, as presenting the most noteworthy and new features of the time; but we must not forget that though cryptogams were deposed from the high position they held in the Palæozoic, they still existed; and there are more especially many interesting species of ferns and equisetums in the Cretaceous and Eocene rocks. These are, however, of moderntypes; and it is remarkable that some of them appear to have continued without even specific change from the later Cretaceous up to the present time. A striking illustration of this is afforded by two ferns discovered side by side in the oldest Eocene beds72of the plains west of Red River, and described in Dr. G. M. Dawson’s report on the 49th parallel. One of these is the well-known and very commonOnoclea sensibilis(Fig. 157), or sensitive fern of Eastern America.73This species came into existence at latest at the close of the Cretaceous, and has apparently been continued in America up to the present time. In Europe, where it does not now live, it occurs as a fossil in Eocene beds in the Isle of Mull. The other isDavallia tenuifolia(Fig. 158), a delicate little plant belonging to a genus not now represented in America, and to a species at present found only in Asia. Yet this species alsolived in America in early Eocene times, but has since been banished, though its former companion, theOnoclea, still holds its ground. Such cases of specific persistence along with great changes of habitat are very instructive as to the permanence of species.
Count Saporta, whose just remarks on the marvellously sudden incoming of the Cretaceous flora we have already referred to, also notices the fact that the families and genera represented in this flora are a most miscellaneous and unconnected assemblage, showing either the simultaneous appearance of many dissimilar types, or requiring us to believe in the existence of these and of intermediate forms for a very long period before that in which they are first found. This may, however, be placed in connection with the appearance of an exogenous tree (Syringoxylon) in the Devonian, referred to in a previous chapter. It would be a strange and now little suspected case of imperfection of the record, if it should be found that trees of this type were lurking in exceptional corners through all the vast periods between the Devonian and the Cretaceous, to burst forth in unwonted variety and luxuriance in the latter period.
The new Cretaceous flora appears first in beds which had been recently elevated from the ocean of the great Cretaceous subsidence; and when it first flourished, in temperate regions at least, the continents were of small dimensions, and broken up into groups of islands. Farther, America would seem to have had precedence of the Eastern Continent, and the Arctic of the Temperate regions. Thus on the elevation of the later Cretaceous land, plants previously established in the far north spread themselves southward, over newly-raised lands, radiating from the polar regions into Europe, Asia, and America. This seems the only way of accounting for the similarity of the plants in these distant countries. The new flora of the Upper Cretaceous in its journey southward met with a climate probably warmer than the present, yet not so warm as to prevent treessimilar to those now living in the same latitudes from flourishing.
Let us now trace this flora through the succeeding ages, in which I shall follow pretty closely some general statements made by Count De Saporta in memoirs recently published.
Eocene Leaves.
Fig. 159.—Eocene Leaves. From Aix.
a,Quercus antecedens(Saporta).b,Diospyros pyrifolia(Saporta).c,Myrica Mathesonii(Saporta).
At the beginning of the Eocene we find a humid and warm climate in Europe, with great forests of oaks, chestnuts, laurels, giant pines, and other genera, some of them still European, others Asiatic or American, and many of them survivors of the Cretaceous (Figs. 159 to 162); and at the same period similar forests overspread those great plains of North America which were rising from out the Cretaceous sea, and there vast swampy beds were formed of vegetabledébris, giving origin to beds of brown coal, some of them eighteen feet in thickness. Then came in Europe and Asia that great subsidence under the sea, during which the Nummuline limestones were deposited, and when the old continent was resolved again into an archipelago of islands, perhaps closely connectedwith more southern lands. This led to a great increase of southern forms of plants, which does not seem to have occurred to the same extent in America, where the flora is more continuous, though showing a warmer climate in the older than in the newer Eocene. At this period Palms, Screw pines, Proteaceous shrubs, Myrtles, Acacias, and other plantsof the character of those of more southern climates were dominant in Europe (Fig. 163). The well-known beds of Bournemouth, in the south of England,74contain a rich flora of the Eocene age, perhaps of its middle period, and reminding us of the forests of sub-tropical India or Australia.
An Ancient Clover.
Fig. 160.—An Ancient Clover (Trifolium palæogæum, Saporta). Eocene. Aix.
An Eocene Maple.
Fig. 161.—An Eocene Maple (Acer sextianus, Saporta). Aix.
A European Magnoli of the Eocene.
Fig. 162.—A European Magnoli of the Eocene (M. dianæ, Saporta). Aix.
Flower and Leaf of Bombax sepultiflorum.
Fig. 163.—Flower and Leaf ofBombax sepultiflorum. Eocene of Aix.—After Saporta.
A European representative of the Silk-cotton-tree of the East Indies and Tropical America.
Gradual elevation of the land favoured for a time the extension of these plants, and the warmth of the climate allowed them to extend even into Arctic latitudes. But in the middle of the Eocene another subsidence occurred, which exterminated much of the Eocene flora, and was perhaps accompanied with a reduction of temperature, in which the more northern lands became covered with great forests of trees allied to the Pines. In England a remarkable deposit ofthis age is that of Bovey Tracey, in Devonshire, where beds of clay and brown coal have afforded a rich flora of American and southern types. TheSequoiashown inFig. 164abounds at this place, and is a near relation to the celebrated “big trees” of California; theCinnamomuminFig. 165is a type equally foreign from modern England. It is a curious feature of the Bovey deposit that immediately above these Eocene beds, holding a rich flora of warm temperate character, are glacial clays with leaves of Arctic willows and of the dwarf birch, indicating a climate much more severe than that of the British Islands at present.75
Branch and Fruit of Sequoia Couttsiae.
Fig. 164.—Branch and Fruit ofSequoia Couttsiæ(Heer). Eocene. England.
In the Miocene period the land again rose, and the northern flora spread itself southward equally over Europe, Asia, and America, so that the Miocene flora of all these regions is very similar; and this Miocene flora continues substantially to this day in Eastern America and Eastern Asia, except that it hasbeen greatly reduced in number of species by the intervention of the cold glacial period; but in Europe and Western America it has been largely replaced by other apparently more modern species.
Cinnamomum Scheuchzeri.
Fig. 165.—Cinnamomum Scheuchzeri(Heer). Eocene. England.
A striking result of recent discoveries is the fact that in Cretaceous and Eocene times a very warm climate prevailed in the extreme Arctic regions, and trees of temperate latitudes grew there freely. In the recent Arctic expedition, Captain Fielden found in latitude 81° 40', within 600 miles of the Pole, a bed of lignite, from twenty-five to thirty feet in thickness, associated with remains of plants such as now grow only in temperate latitudes.
“From the character of the plant-remains, Dr. Heer infers that the lignite of this locality represents an ancient peat-moss, which must have been of wide extent, with reeds, sedges, birches, poplar, and certain conifers growing on its banks; while the higher and drier ground in the neighbourhood probably supported a growth of pines and firs, with elms and hazel-bushes. The remains of water-lilies suggest the existence of a fresh-water lake in the old peat-moss, which must have remained unfrozen during a great part of the year.”
It is to be observed with reference to the age of these beds, that as the Later Cretaceous and Eocene flora of Europe and America migrated from the north, the plants found in the beds of that age in the temperate latitudes may really be somewhat older in the Arctic regions, a fact which produces some uncertainty as to their actual age.
The warmth required for the growth of luxuriant forests near the Pole might be secured by a different distribution of land and water, and of the oceanic currents, but the requirements of plants as to light seem more difficult to meet, and it has been doubted whether species similar to those which are accustomed in modern times to regular alternations of day and night could submit to the long Arctic winter darkness. It is known, however, that in conservatories in Northern Russia plants supplied with heat and moisture can endure in winter great deprivation of light, and at Disco, in Greenland, roses and fuchsias flourish as house plants.76These facts show that if there were sufficient light and heat in summer, a great number of the plants of temperate latitudes could endure extreme cold and much deprivation of light in winter.
It may be well here to inform the reader that some confusion as to the succession of the Cretaceous and Tertiary floras in America has arisen from the fact that the plants which are evidently Eocene in Greenland and America have been until lately incorrectly regarded as Miocene in Europe. In the
Western States, the Dakota group of Lesquereux is overlain by 2000 feet of Cretaceous beds, containing the marine shells characteristic of that age, but no plants. But in Vancouver’s Island these same Upper Cretaceous beds contain an abundant flora, which some botanists have called Tertiary for the reason already mentioned. Above the 2000 feet of marine beds overlying the Dakota group is the Lower Lignite group of Lesquereux, holding many fossil plants, including Palms and other evidences of a warmer climate than that of the Cretaceous, and which constitute a Lower Eocene flora corresponding in some respects to that of Europe. This is succeeded by an Upper Lignite group, also Eocene, but representing a more temperate climate, and therefore resembling more nearly the Cretaceous flora. This is nearly identical with the so-called Miocene of Greenland, Alaska, and Mackenzie River, which the facts collected by the Canadian geologists have shown to be really Eocene.77But the Canadian reports containing these facts are comparatively little known in Europe, hence incorrect ideas as to the succession of these floras have been handed from one writer to another.
To those who adopt extreme views as to the refrigeration of the northern hemisphere in so-called glacial times, there is great difficulty in accounting for the continued existence of the early Tertiary flora; but if we adopt moderate views as to this, and demand merely a great subsidence, with much reduction of mean temperature, we may suppose that the plants previously existing were preserved on insular spots, whence they were ready to recolonize the land on its emergence from the sea. It seems certain, however, that our continents never regained, after the Glacial period, the exuberance of plant life which they presented in the Miocene and earlier Pliocene; and we shall find that this statement applies to the world of animals as well as to that of plants. This reduction was more extreme in Europe than in Eastern Asia and Eastern
America, and the fact is thus accounted for in a recent lecture by Prof. Asa Gray:—
“I conceive that three things have conspired to this loss. First, Europe, hardly extending south of latitude 40°, is all within the limits generally assigned to severe glacial action. Second, its mountains trend east and west, from the Pyrenees to the Carpathians and the Caucasus beyond, near its southern border; and they had glaciers of their own, which must have begun their operations, and poured down the northward flanks, while the plains were still covered with forest, on the retreat from the great ice-wave coming from the north. Attacked both on front and rear, much of the forest must have perished then and there. Third, across the line of retreat of those which may have flanked the mountain-ranges, or were stationed south of them, stretched the Mediterranean, an impassable barrier. Some hardy trees may have eked out their existence on the northern shore of the Mediterranean and the Atlantic coast. But we doubt not,Taxodiumand Sequoias, Magnolias and Liquidambars, and even Hickories and the like, were among the missing. Escape by the east, and rehabilitation from that quarter until a very late period, were apparently prevented by the prolongation of the Mediterranean to the Caspian, and thence to the Siberian ocean. If we accept the supposition of Nordenskiöld, that, anterior to the Glacial period, Europe was ‘bounded on the south by an ocean extending from the Atlantic over the present deserts of Sahara and Central Asia to the Pacific,’ all chance of these American types having escaped from or re-entered Europe from the south and east is excluded. Europe may thus be conceived to have been for a time somewhat in the condition in which Greenland is now, and indeed to have been connected with Greenland in this or in earlier times.78Such a junction, cutting off access of the Gulf Stream to the Polar Sea,would, as some think, other things remaining as they are, almost of itself give glaciation to Europe. Greenland may be referred to, by way of comparison, as a country which, having undergone extreme glaciation, bears the marks of it in the extreme poverty of its flora, and in the absence of the plants to which its southern portion, extending six degrees below the Arctic Circle, might be entitled. It ought to have trees, and might support them. But since destruction by glaciation no way has been opened for their return. Europe fared much better, but suffered in its degree in a similar way.
“Turning for a moment to the American continent for a contrast, we find the land unbroken and open down to the tropic, and the mountains running north and south. The trees, when touched on the north by the on-coming refrigeration, had only to move their southern border southward, along an open way, as far as the exigency required; and there was no impediment to their due return. Then the more southern latitude of the United States gave great advantage over Europe. On the Atlantic border, proper glaciation was felt only in the northern part, down to about latitude 40°. In the interior of the country, owing doubtless to greater dryness and summer heat, the limit receded greatly northward in the Mississippi Valley, and gave only local glaciers to the Rocky Mountains; and no volcanic outbreaks or violent changes of any kind have here occurred since the types of our present vegetation came to the land. So our lines have been cast in pleasant places, and the goodly heritage of forest-trees is one of the consequences.
“The still greater richness of North-east Asia in arboreal vegetation may find explanation in the prevalence of particularly favourable conditions, both ante-glacial and recent. The trees of the Miocene circumpolar forest appear to have found there a secure home; and the Japanese islands, to which most of these trees belong, must be remarkably adapted to them. The situation of these islands—analogous to that of Great Britain, but with the advantage of lower latitude and greater sunshinetheir ample extent north and south, their diversified configuration, their proximity to the great Pacific gulf-stream, by which a vast body of warm water sweeps along their accentuated shores, and the comparatively equable diffusion of rain throughout the year, all probably conspire to the preservation and development of an originally ample inheritance.”
The comparative paucity in species of the west coast of America, though the Sequoias and some other forms which have perished elsewhere are retained there, is admitted to be exceptional, and not easily explained, except by the supposition of peculiar local conditions affecting the comparatively narrow strip of land between the Rocky Mountains and coast ranges, and the Pacific.
To such widely-distributed and varied and complex phenomena as those which have been discussed in the present chapter, it is impossible to do justice in the space at our command. Details in relation to them will be found in the publications of Heer, of Saporta, and of Lesquereux, and are well worthy of study by botanists, to whom alone they can be made fully intelligible. In general, with reference to now prevalent theories of derivation, they present two very dissimilar aspects. No difficulty can be greater to the evolutionist than to account for the simultaneous appearance of so many modern generic forms in the Cretaceous; and the fact of many of the genera presenting more and more species the farther we trace them back is a strange anomaly of evolution. On the other hand, the number of species continuing unchanged from the Eocene to the Modern, the others only slightly modified, and the representative species occurring in the floras of the old and new continents, appear to many to give great support to the doctrine of gradual transformation of species. Farther facts and farther comprehension of the difference between species and races will be necessary to the settlement of these questions. In the meantime it would appear that the Jurassic flora rapidly gave place, at a particularpoint of geological time, to that of the modern world, and this not merely in one locality, but over the whole northern hemisphere; and there are apparently similar facts in the southern hemisphere as well. It farther appears that each genus was at first represented by many species, and that as time went on these were gradually reduced to a few best suited to survive; and that the changes of climate and level which occurred distributed these over different parts of the continents in a way at first sight very anomalous, but which Prof. Gray somewhat quaintly represents as follows:—
“It is as if Nature, when she had enough species of a genus to go round the four floral regions (Europe, East Asia, West America, and East America), dealt them fairly one at least to each quarter of our zone; but when she had only two of some peculiar kind, gave one to us, and the other to Japan, Mantchuria, or the Himalayas; and when she had only one, divided it between the two partners on the opposite sides of the table.”
Lastly, it seems very probable that many so-called species are nothing more than varietal forms, which may very well be modified descendants of Miocene or Eocene plants now figuring in our lists under different names.