The Student's Elements of Geology Part 23

But let us suppose that no fruit, seed, or flower had ever been met with in a fossil state, we should still have been indebted to the persevering labours of botanical palaeontologists for one of the grandest scientific discoveries for which the present century is remarkable-- namely, the proofs now established of the prevalence of a mild climate and a rich arborescent flora in the arctic regions in that Miocene epoch on the history of which we are now entering. It may be useful if I endeavour to give the reader in a few words some idea of the nature of the evidence of these important conclusions, to show how far they may be safely based on fossil leaves alone. When we begin by studying the fossils of the Newer Pliocene deposits, such as those of the Upper Val d'Arno, before alluded to, we perceive that the fossil foliage agrees almost entirely with the trees and shrubs of a modern European forest. In the plants of the Older Pliocene strata of the same region we observe a larger proportion of species and genera which, although they may agree with well-known Asiatic or other foreign types, are at present wanting in Italy. If we then examine the Miocene formations of the same country, exotic forms become more abundant, especially the palms, whether they belong to the European or American fan-palms, Chamaerops and Sabal, or to the more tropical family of the date-palms or Phoenicites, which last are conspicuous in the Lower Miocene beds of Central Europe. Although we have not found the fruit or flower of these palms in a fossil state, the leaves are so characteristic that no one doubts the family to which they belong, or hesitates to accept them as indications of a warm and sub-tropical climate.

When the Miocene formations are traced to the northward of the 50th degree of lat.i.tude, the fossil palms fail us, but the greater proportion of the leaves, whether identical with those of existing European trees or of forms now unknown in Europe, which had accompanied the Miocene palms, still continue to characterise rocks of the same age, until we meet with them not only in Iceland, but in Greenland, in lat.i.tude 70 degrees N., and in Spitzbergen, lat.i.tude 78 degrees 56', or within about 11 degrees of the pole, and under circ.u.mstances which clearly show them to have been indigenous in those regions, and not to have been drifted from the south (see Chapter 15). Not only, therefore, has the botanist afforded the geologist much palaeontological a.s.sistance in identifying distinct tertiary formations in distant places by his power of accurately discriminating the forms, veining, and microscopic structure of leaves or wood, but, independently of that exact knowledge derivable from the organs of fructification, we are indebted to him for one of the most novel, unexpected results of modern scientific inquiry.

The Miocene formations of Switzerland have been called MOLa.s.sE, a term derived from the French MOL, and applied to a SOFT, incoherent, greenish sandstone, occupying the country between the Alps and the Jura. This mola.s.se comprises three divisions, of which the middle one is marine, and being closely related by its sh.e.l.ls to the faluns of Touraine, may be cla.s.sed as Upper Miocene. The two others are fresh-water, the upper of which may be also grouped with the faluns, while the lower must be referred to the Lower Miocene, as defined in the next chapter.

UPPER FRESH-WATER MOLa.s.sE.

This formation is best seen at Oeningen, in the valley of the Rhine, between Constance and Schaffhausen, a locality celebrated for having produced in the year 1700 the supposed human skeleton called by Scheuchzer "h.o.m.o diluvii testis," a fossil afterwards demonstrated by Cuvier to be a reptile, or aquatic salamander, of larger dimensions than even its great living representative, the salamander of j.a.pan.

The Oeningen strata consist of a series of marls and limestones, many of them thinly laminated, and which appear to have slowly acc.u.mulated in a lake probably fed by springs holding carbonate of lime in solution. The elliptical area over which this fresh-water formation has been traced extends, according to Sir Roderick Murchison, for a distance of ten miles east and west from Berlingen, on the right bank of the river to w.a.n.gen, and to Oeningen, near Stein, on the left bank. The organic remains have been chiefly derived from two quarries, the lower of which is about 550 feet above the level of the Lake of Constance, while the upper quarry is 150 feet higher. In this last, a section thirty feet deep displays a great succession of beds, most of them splitting into slabs and some into very thin laminae. Twenty-one beds are enumerated by Professor Heer, the uppermost a bluish-grey marl seven feet thick, with organic remains, resting on a limestone with fossil plants, including leaves of poplar, cinnamon, and pond- weed (Potamogeton), together with some insects; while in the bed No. 4, below, is a bituminous rock, in which the Mastodon tapiroides, a characteristic Upper Miocene quadruped, has been met with. The 5th bed, two or three inches thick, contains fossil fish, e.g., Leuciscus (roach), and the larvae of dragon-flies, with plants such as the elm (Ulmus), and the aquatic Chara. Below this are other plant-beds; and then, in No. 9, the stone in which the great salamander (Andrias Scheuchzeri) and some fish were found. Below this other strata occur with fish, tortoises, the great salamander before alluded to, fresh-water mussels, and plants. In No. 16 the fossil fox of Oeningen, galecynus Oeningensis, Owen, was obtained by Sir R. Murchison. To this succeed other beds with mammalia (Lagomys), reptiles, (Emys), fish, and plants, such as walnut, maple, and poplar. In the 19th bed are numerous fish, insects, and plants, below which are marls of a blue indigo colour.

In the lower quarry eleven beds are mentioned, in which, as in the upper, both land and fresh-water plants and many insects occur. In the 6th, reckoning from the top, many plants have been obtained, such as Liquidambar, Daphnogene, Podogonium, and Ulmus, together with tortoises, besides the bones and teeth of a ruminant quadruped, named by H. von Meyer Palaeomeryx eminens. No. 9 is called the insect-bed, a layer only a few inches thick, which, when exposed to the frost, splits into leaves as thin as paper. In these thin laminae plants such as Liquidambar, Daphnogene, and Glyptostrobus, occur, with innumerable insects in a wonderful state of preservation, usually found singly. Below this is an indigo- blue marl, like that at the bottom of the higher quarry, resting on yellow marl ascertained to be at least thirty feet thick.

(FIGURE 138. Cinnamomum polymorphum, Ad. Brong. Upper and Lower Miocene.

a. Leaf.

b. Flower, natural size; Heer Plate 93 Figure 28.

c. Ripe fruit of Cinnamomum polymorphum, from Oeningen; Heer, Plate 94 Figure 14.

d. Fruit of recent Cinnamomum camphorum of j.a.pan; Heer, Plate 152 Figure 18.)

All the above fossil-bearing strata were evidently formed with extreme slowness.

Although the fossiliferous beds are, in the aggregate, no more than a few yards in thickness, and have only been examined in the small area comprised in the two quarries just alluded to, they give us an insight into the state of animal and vegetable life in part of the Upper Miocene period, such as no other region in the world has elsewhere supplied. In the year 1859, Professor Heer had already determined no less than 475 species of plants and more than 800 insects from these Oeningen beds. He supposes that a river entering a lake floated into it some of the leaves and land insects, together with the carca.s.ses of quadrupeds, among others a great Mastodon. Occasionally, during tempests, twigs and even boughs of trees with their leaves were torn off and carried for some distance so as to reach the lake. Springs, containing carbonate of lime, seem at some points to have supplied calcareous matter in solution, giving origin locally to a kind of travertin, in which organic bodies sinking to the bottom became hermetically sealed up. The laminae, says Heer, which immediately succeed each other were not all formed at the same season, for it can be shown that, when some of them originated, certain plants were in flower, whereas, when the next of these layers was produced, the same plants had ripened their fruit. This inference is confirmed by independent proofs derived from insects. The princ.i.p.al insect-bed is rarely two inches thick, and is composed, says Heer, of about 250 leaf-like laminae, some of which were deposited in the spring, when the Cinnamomum polymorphum (Figure 138) was in flower, others in summer, when winged ants were numerous, and when the poplar and willow had matured their seed; others, again, in autumn, when the same Cinnamomum polymorphum (Figure 138) was in fruit, as well as the liquidambar, oak, clematis, and many other plants. The ancient lake seems to have had a belt of poplars and willows round its borders, countless leaves of which were imbedded in mud, and together with them, at some points, a species of reed, Arundo, which was very common.

One of the most characteristic shrubs is a papilionaceous and leguminous plant of an extinct genus, called by Heer Podogonium, of which two species are known.

Entire twigs have been found with flowers, and always without leaves, as the flowers evidently came out, as in the poplar and willow tribe, before any leaves made their appearance. Other specimens have been obtained with ripe fruits accompanied by leaves, which resemble those of the tamarind, to which it was evidently allied, being of the family Caesalpineae, now proper to warmer regions.

(FIGURE 139. Acer trilobatum, normal form; Heer, Flora Tert. Helv. Plate 114 Figure 2. Size 1/2 diam. (Part only of the long stalk of the original fossil specimen is here given ). Upper Miocene, Oeningen; also found in Lower Miocene of Switzerland.)

(FIGURE 140. Acer trilobatum.

a. Abnormal variety of leaf; Heer, Plate 110 Figure 16.

b. Flower and bracts, normal form; Heer, Plate 111 Figure 21.

c. Half a seed-vessel; Heer, Plate 111 Figure 5.)

(FIGURE 141. Plata.n.u.s aceroides, Gopp.; Heer, Plate 88 Figures 5-8. Size 2/3 diam. Upper Miocene, Oeningen.

a. Leaf.

b. The core of a bundle of pericarps.

c. Single fruit or pericarp, natural size.)

The Upper Miocene flora of Oeningen is peculiarly important, in consequence of the number of genera of which not merely the leaves, but, as in the case of the Podogonium just mentioned, the fruit also and even the flower are known. Thus there are nineteen species of maple, ten of which have already been found with fruit. Although in no one region of the globe do so many maples now flourish, we need not suspect Professor Heer of having made too many species in this genus when we consider the manner in which he has dealt with one of them, Acer trilobatum, Figures 139 and 140. Of this plant the number of marked varieties figured and named is very great, and no less than three of them had been considered as distinct species by other botanists, while six of the others might have laid claim, with nearly equal propriety, to a like distinction. The common form, called Acer trilobatum, Figure 139, may be taken as a normal representative of the Oeningen fossil, and Figure 140, as one of the most divergent varieties, having almost four lobes in the leaf instead of three.

(FIGURE 142. Smilax sagittifera; Heer, Plate 30 Figure 7. Size 1/2 diameter.

a. Leaf.

b. Flower magnified, one of the six petals wanting at d. Upper Miocene, Oeningen.

c. Smilax obtusifolia; Heer, Plate 30 Figure 9; natural size. Upper Miocene, Oeningen.)

(FIGURE 143. Fruit of the fossil and recent species of Hakea, a genus of Proteaceae.

a. Leaf of fossil species, Hakea salicina. Upper Miocene, Oeningen; Heer Plate 97 Figure 29. 1/3 diameter.

b. Impression of woody fruit of same, showing thick stalk. 2/3 diameter.

c. Seed of same, natural size.

d. Fruit of living Australian species, Hakea saligna, R. Brown. 1/2 diameter.

e. Seed of same, natural size.)

Among the conspicuous genera which abounded in the Miocene period in Europe is the plane-tree, Plata.n.u.s, the fossil species being considered by Heer to come nearer to the American P. occidentalis than to P. orientalis of Greece and Asia Minor. In some of the fossil specimens the male flowers are preserved. Among other points of resemblance with the living plane-trees, as we see them in the parks and squares of London, fossil fragments of the trunk are met with, having pieces of their bark peeling off.

The vine of Oeningen, Vitis teutonica, Ad. Brong, is of a North American type.

Both the leaves and seeds have been found at Oeningen, and bunches of compressed grapes of the same species have been met with in the brown coal of Wetteravia in Germany. No less than eight species of smilax, a monocotyledonous genus, occur at Oeningen and in other Upper Miocene localities, the flowers of some of them, as well as the leaves, being preserved; as in the case of the very common fossil, S. sagittifera, Figure 142, a.

Leaves of plants supposed to belong to the order Proteaceae have been obtained partly from Oeningen and partly from the lacustrine formation of the same age at Locle in the Jura. They have been referred to the genera Banksia, Grevillea, Hakea, and Persoonia. Of Hakea there is the impression of a supposed seed- vessel, with its characteristic thick stalk and seeds, but as the fruit is without structure, and has not yet been found attached to the same stem as the leaf, the proof is incomplete.

To whatever family the foliage hitherto regarded as proteaceous by many able palaeontologists may eventually be shown to belong, we must be careful not to question their affinity to that order of plants on those geographical considerations which have influenced some botanists. The nearest living Proteaceae now feel the in Abyssinia in lat.i.tude 20 degrees N., but the greatest number are confined to the Cape and Australia. The ancestors, however, of the Oeningen fossils ought not to be looked for in such distant regions, but from that European land which in Lower Miocene times bore trees with similar foliage, and these had doubtless an Eocene source, for cones admitted by all botanists to be proteaceous have been met with in one division of that older Tertiary group (see Figure 206 Chapter 16). The source of these last, again, must not be sought in the antipodes, for in the white chalk of Aix-la-Chapelle leaves like those of Grevillea and other proteaceous genera have been found in abundance, and, as we shall see in Chapter 17, in a most perfect state of preservation. All geologists agree that the distribution of the Cretaceous land and sea had scarcely any connection with the present geography of the globe.

(FIGURE 144. Glyptostrobus Europaeus.

Branch with ripe fruit; Heer, Plate 20 Figure 1. Upper Miocene, Oeningen.)

In the same beds with the supposed Proteaceae there occurs at Locle a fan-palm of the American type Sabal (for genus see Figure 151), a genus which ranges throughout the low country near the sea from the Carolinas to Florida and Louisiana. Among the Coniferae of Upper Miocene age is found a deciduous cypress nearly allied to the Taxodium distichum of North America, and a Glyptostrobus (Figure 144), very like the j.a.panese G. heterophyllus, now common in our shrubberies.

Before the appearance of Heer's work on the Miocene Flora of Switzerland, Unger and Goppert had already pointed out the large proportion of living North American genera which distinguished the vegetation of the Miocene period in Central Europe. Next in number, says Heer, to these American forms at Oeningen the European genera preponderate, the Asiatic ranking in the third, the African in the fourth, and the Australian in the fifth degree. The American forms are more numerous than in the Italian Pliocene flora, and the whole vegetation indicates a warmer climate than the Pliocene, though not so high a temperature as that of the older or Lower Miocene period.

The conclusions drawn from the insects are for the most part in perfect harmony with those derived from the plants, but they have a somewhat less tropical and less American aspect, the South European types being more numerous. On the whole, the insect fauna is richer than that now inhabiting any part of Europe.

No less than 844 species are reckoned by Heer from the Oeningen beds alone, the number of specimens which he has examined being 5080. The entire list of Swiss species from the Upper and Lower Miocene together amount to 1322. Almost all the living families of Coleoptera are represented, but, as we might have antic.i.p.ated from the preponderance of arborescent and ligneous plants, the wood-eating beetles play the most conspicuous part, the Buprestidae and other long-horned beetles being particularly abundant.

(FIGURE 145. Harpactor maculipes, Heer. Upper Miocene, Oeningen.)

The patterns and some remains of the colours both of Coleoptera and Hemiptera are preserved at Oeningen, as, for example in Harpactor (Figure 145), in which the antennae, one of the eyes, and the legs and wings are retained. The characters, indeed, of many of the insects are so well defined as to incline us to believe that if this cla.s.s of the invertebrata were not so rare and local, they might be more useful than even the plants and sh.e.l.ls in settling chronological points in geology.

MIDDLE OR MARINE MOLa.s.sE (UPPER MIOCENE) OF SWITZERLAND.

It was before stated that the Miocene formation of Switzerland consisted of, first, the upper fresh-water mola.s.se, comprising the lacustrine marls of Oeningen; secondly, the marine mola.s.se, corresponding in age to the faluns of Touraine; and thirdly, the lower fresh-water mola.s.se. Some of the beds of the marine or middle series reach a height of 2470 feet above the sea. A large number of the sh.e.l.ls are common to the faluns of Touraine, the Vienna basin, and other Upper Miocene localities. The terrestrial plants play a subordinate part in the fossiliferous beds, yet more than ninety of them are enumerated by Heer as belonging to this falunian division, and of these more than half are common to subjacent Lower Miocene beds, while a proportion of about forty-five in one hundred are common to the overlying Oeningen flora. Twenty-six of the ninety-two species are peculiar.

UPPER MIOCENE OF THE BOLDERBERG, IN BELGIUM.

(FIGURE 146. Oliva Dufresnii, Bast. Bolderberg, Belgium; natural size.

a. Front view.

b. Back view.)

In a small hill or ridge called the Bolderberg, which I visited in 1851, situated near Ha.s.selt, about forty miles E.N.E. of Brussels, strata of sand and gravel occur, to which M. Dumont first called attention as appearing to const.i.tute a northern representative of the faluns of Touraine. On the whole, they are very distinct in their fossils from the two upper divisions of the Antwerp Crag before mentioned (Chapter 13), and contain sh.e.l.ls of the genera Oliva, Conus, Ancillaria, Pleurotoma, and Cancellaria in abundance. The most common sh.e.l.l is an Olive (Figure 146), called by Nyst Oliva Dufresnii; and const.i.tuting, as M. Bosquet observes, a smaller and shorter variety of the Bordeaux species.

So far as the sh.e.l.ls of the Bolderberg are known, the proportion of recent species agrees with that in the faluns of Touraine, and the climate must have been warmer than that of the Coralline Crag of England.

UPPER MIOCENE BEDS OF THE VIENNA BASIN.

In South Germany the general resemblance of the sh.e.l.ls of the Vienna tertiary basin with those of the faluns of Touraine has long been acknowledged. In the late Dr. Hornes's excellent work on the fossil mollusca of that formation, we see accurate figures of many sh.e.l.ls, clearly of the same species as those found in the falunian sands of Touraine.

According to Professor Suess, the most ancient and purely marine of the Miocene strata in this basin consist of sands, conglomerates, limestones, and clays, and they are inclined inward, or from the borders of the trough towards the centre, their outcropping edges rising much higher than the newer beds, whether Miocene or Pliocene, which overlie them, and which occupy a smaller area at an inferior elevation above the sea. M. Hornes has described no less than 500 species of gasteropods, of which he identifies one-fifth with living species of the Mediterranean, Indian, or African seas, but the proportion of existing species among the lamellibranchiate bivalves exceeds this average. Among many univalves agreeing with those of Africa on the eastern side of the Atlantic are Cypraea sanguinolenta, Buccinum lyratum, and Oliva flammulata. In the lowest marine beds of the Vienna basin the remains of several mammalia have been found, and among them a species of Dinotherium, a Mastodon of the Trilophodon family, a Rhinoceros (allied to R. megarhinus, Christol), also an animal of the hog tribe, Listriodon, von Meyer, and a carnivorous animal of the canine family. The Helix turonensis (Figure 38 Chapter 3), the most common land sh.e.l.l of the French faluns, accompanies the above land animals. In a higher member of the Vienna Miocene series are found Dinotherium giganteum (Figure 136 Chapter 14), Mastodon longirostris, Rhinoceros Schleiermacheri, Acerotherium incisivum, and Hippotherium gracile, all of them equally characteristic of an Upper Miocene deposit occurring at Eppelsheim, in Hesse Darmstadt; a locality also remarkable as having furnished in lat.i.tude 49 degrees 50 north the bone of a large ape of the Gibbon kind, the most northerly example yet discovered of a quadrumanous animal.

(FIGURE 147. Amphistegina Hauerina, d'Orbigny. Upper Miocene strata, Vienna.)

M. Alcide d'Orbigny has shown that the foraminifera of the Vienna basin differ alike from the Eocene and Pliocene species, and agree with those of the faluns, so far as the latter are known. Among the Vienna foraminifera, the genus Amphistegina (Figure 147) is very characteristic, and is supposed by d'Archiac to take the same place among the Rhizopods of the Upper Miocene era which the Nummulites occupy in the Eocene period.

The flora of the Vienna basin exhibits some species which have a general range through the whole Miocene period, such as Cinnamomum polymorphum (Figure 138 Chapter 14), and C. Scheuchzeri, also Planera Richardi, Mich., Liquidambar europaeum (Figure 135 Chapter 13) Juglans bilinica, Ca.s.sia ambigua, and C.