Part 8

[Sidenote: Fig. 96. _Acer trilobatum_, a three-lobed palmate leaf, like that of the Maple, with the lobes unequal, inciso-dentate, the lateral ones spreading, found at Œningen. Fig. 97. _Ulmus Bronnii_, a petiolate leaf, like that of the Elm, unequally ovato-acuminate, feather-veined and toothed, found in Bohemia. Fig. 98. _Rhamnus Aizoon_, a petiolate elliptical obtuse feather-veined leaf, with an entire margin, found in Styria.]

The most striking characters of the Miocene epoch consist in the mixture of exotic forms of warm regions with those of temperate climates. Unger says that it resembles that of the southern part of North America. Thus we meet with Palms, such as species of Flabellaria and Phœnicites, a kind of Bamboo called Bambusium sepultum; Lauraceæ, as Daphnogene and Laurus; Combretaceæ, as Getonia and Terminalia; Leguminosæ, as Phaseolites, Desmodophyllum, Dolichites, Erythrina, Bauhinia, Mimosites, and Acacia--all plants having their living representatives in warm climates; Echitonium, Plumiera, and other Apocynaceæ of equatorial regions; Comptonia (Fig. 95), a Proteaceous genus, and Steinhauera, a Cinchonaceous genus; mingled with species of Acer (Fig. 96), Ulmus (Fig. 97), Rhamnus (Fig. 98); and Amentiferous forms, such as Myrica, Betula, Alnus (Fig. 99), Quercus, Fagus, Carpinus, all belonging to temperate and cold climates. The statements as to the occurrence of Pinus sylvestris and Betula alba among the Miocene fossils have not been founded on complete data. It is by no means easy, even in the present day, to distinguish fragments of dried specimens of Pinus Pumilio from those of P. sylvestris, and from a great many other Pines. The difficulty is still greater in fossils (Hook. Kew Journ. v. 413). There are a very small number of plants belonging to orders with gamopetalous corollas. In the Miocene formation of Lough Neagh in Ireland, and of Mull in Scotland, silicified trunks of considerable size have been found. The Irish silicified wood has been denominated Cupressoxylon Pritchardi from its apparent resemblance to the Cypress. As connected with the Miocene epoch, we may notice the leaf-beds found at Ardtun, in the island of Mull, by the Duke of Argyll.[22] Above and below these beds basalt occurs, and there are peculiar tuff-beds alternating with the leafy deposits. These tuff-beds were formed by the deposit of volcanic dust in pools probably of fresh water. They contain fragments of chalk and flint. The leaves are those of plants allied to the Yew, Rhamnus, Plane, and Alder, along with the fronds of a peculiar Fern, and the stems of an Equisetum. The genera are Taxites or Taxodites (Fig. 100), Rhamnites (Fig. 101), Platanites, Alnites, Filicites, and Equisetum (Fig. 102). In the leaf-beds at Bournemouth Mr. Wanklyn detected several ferns. One is a species of Didymosorus, and shows distinct venation and fructification. Fossilised wood was found in the Arctic Regions by Captain M'Clure. At the N.W. of Banks Land he found trees with trunks 1 foot 7 inches in diameter.

[Sidenote: Fig. 99. _Alnus gracilis_, an ovate-oblong leaf, like that of the Alder, found in Bohemia.]

[Sidenote: Figures 100, 101, 102, exhibit fragments of plants which occur in the leaf-bed at Ardtun Head, in Mull, and which is referred to the Miocene epoch. The figures are from the Duke of Argyll's paper.]

[Sidenote: Fig. 100. _Taxites_, or perhaps _Taxodites Campbellii_, a branch with leaves resembling those of the Yew, or rather those of Taxodium.

Fig. 101. _Rhamnites multinervatus_, a leaf resembling that of Rhamnus.]

[Sidenote: Fig. 102. _Equisetum Campbellii_, a stem like that of an Equisetum of the present day.]

Dr. Oswald Heer[23] has examined the plants preserved in the lignite beds of Bovey Tracey, in Devonshire, and he finds that they belong to the Miocene formation. There is a remarkable coincidence between this and several of the continental fossil floras, such as those of Salzhauser in the Wetterau, Manosque in Provence, and of some parts of Switzerland. Bovey Tracey has no species in common with Iceland, although the Tertiary flora of Iceland belongs to the same period. Two of its species (Corylus MacQuarrii and Platanus aceroides) have been found in the Miocene of Ardtun Head. Even the genera are distinct, with the exception of Sequoia and Quercus. The Bovey Tracey flora has a much more southern character, corresponding entirely with that of the Lower Miocene of Switzerland. It contains three species of Cinnamon, one Laurel, evergreen Figs, one Palm, and large Ferns, thus manifesting a subtropical climate. One of the most important plants is Sequoia Couttsiæ, a Conifer which supplies a link between S. Langsdorfii and S. Sternbergi, the widely-distributed representatives of S. sempervirens and S. gigantea (Wellingtonia), which are Californian trees. Among other characteristic plants may be mentioned Cinnamomum lanceolatum and C. Scheuchzeri; Quercus Lyellii, an evergreen oak; species of evergreen fig (Ficus Falconeri and F. Pengellii), Palmacites Dæmonorops, a prickly twining Rotang-palm; species of Vine (Vitis Hookeri and V. Britannica); Pecopteris lignitum, a large tree-fern; species of Nyssa, at present confined to North America. Among other plants recorded by Heer in his paper are the following:--Laurus primigenia, Daphnogene Ungeri, species of Dryandroides, Andromeda, Vaccinium acheronticum, Echitonium cuspidatum, Gardenia Wetzleri, species of Anona, Nymphæa Doris, Carpolithes Websteri, C. Boveyanus, and other species. In the post-tertiary white clay of Bovey Tracey, Salix cinerea, and a species allied to S. repens, as well as Betula nana, are found.

The Arctic fossil flora (Miocene), according to Heer, amounts to 162 species: Cryptogamia, 18 species, of which 9 are large ferns; Phanerogamia, Coniferæ, 31; Monocotyledons, 14; Dicotyledons, 99. Among the Coniferæ are--Pinus M'Clurii, Sequoia Langsdorffii, Sternbergi, and Couttsiæ, Taxodium dubium, Glyptostrobus europæus, Thujopsis europæa. Among leafy trees are--Fagus Deucalionis, Quercus Olafseni, Platanus aceroides, willows, beeches, Acer, Otopteryx, tulip-tree, walnuts, Magnolia Inglefieldi, Prunus Scottii, Tilia Malmgreni, Corylus M'Quarrii, Alnus Kefersteinii, Daphnogene Kannii, probably one of the Lauraceæ; and among Proteaceæ, MacClintockia? and Hakea. In Greenland are found species of Rhamnus, Paliurus, Cornus, Ilex, Cratægus, Andromeda, Myrica, Ivy, and Vine. From the flora of Spitzbergen, in the Miocene epoch, we may conclude that under 79° N. lat. the mean temperature of the year may have been 41° Fahr., while at the same epoch that of Switzerland was 69°·8 Fahr.; judging from the analogy of floras, it appears that the mean temperature has fallen 6°·9. From this it follows that at Spitzbergen, at 78° N. lat., the mean temperature was perhaps 41°·9 Fahr. In Greenland, at 70°, it would be 49°·1 Fahr., and in Iceland and on the Mackenzie, in lat. 65°, it would be 52°·7 Fahr. At the Miocene epoch the temperature seems to have been much more uniform, the mean heat diminishing much more gradually in proportion as the pole was approached. The isothermal line of 32° Fahr. might have fallen upon the pole, while now it is situated under 58° N. (See Heer's conclusions as to changes of temperature depending on proportion of sea and land, eccentricity of the earth, and the earth moving through warm and cold spaces in the universe--Ann. Nat. Hist. 4th ser. i. 66.)

In speaking of the Polar flora of former epochs, Heer says that every plant executes a slow and continuous migration. These migrations, the starting-point of which is the distant past, are recorded in the rocks; and the interweaving of the carpets of flowers which adorn our present creation retraces them for us in its turn. For the vegetation of the present day is closely connected with that of preceding epochs; and throughout all these vegetable creations reigns _one_ thought, which not only reveals itself around us by thousands upon thousands of images, but strikes us everywhere in the icy regions of the extreme north. Organic nature may become impoverished there, and even disappear when a cold mantle of ice extends over the whole earth; but where the flowers die the rocks speak, and relate the marvels of creation; they tell us that even in the most distant countries, and in the remotest parts, nature was governed by the same laws and the same harmony as immediately around us.[24]

_FLORA OF THE PLIOCENE EPOCH._

The flora of the Pliocene epoch has a great analogy to that of the temperate regions of Europe, North America, and Japan. We meet with Coniferæ, Amentiferæ, Rosaceæ, Leguminosæ, Rhamnaceæ, Aceraceæ, Aquifoliaceæ, Ericaceæ, and many other orders. There is a small number of Dicotyledons with gamopetalous corollas. The twenty species with such corollas recognised by Brongniart are referred to the Hypogynous Gamopetalous group of Exogens, which in the general organisation of the flowers approach nearest to Dialypetalæ. In this flora there is the predominance of Dicotyledons in number and variety; there are few Monocotyledons. No species appear to be identical, at least with the plants which now grow in Europe. Thus the flora of Europe, even at the most recent geological epoch of the Tertiary period, was very different from the European flora of the present day.

Taking the natural orders which have at least four representatives, Raulin[25] gives the following statement as to the Tertiary flora of central Europe. The Eocene flora of Europe is composed of 128 species, of which 115 belong to Algæ, Characeæ, Pandanaceæ, Palmæ, Naiadaceæ, Malvaceæ, Sapindaceæ, Proteaceæ, Papilionaceæ, and Cupressineæ. The Miocene flora has 112 species, of which 69 belong to Algæ, Palmæ, Naiadaceæ, Apocynaceæ, Aceraceæ, Lauraceæ, Papilionaceæ, Platanaceæ, Quercineæ, Myricaceæ, and Abietineæ. The Pliocene flora has 258 species, of which 226 belong to Algæ, Fungi, Musci, Filices, Palmæ, Ericaceæ, Aquifoliaceæ, Aceraceæ, Ulmaceæ, Rhamnaceæ, Papilionaceæ, Juglandaceæ, Salicaceæ, Quercineæ, Betulaceæ, Taxaceæ, Cupressineæ, and Abietineæ. The Eocene species are included in genera which belong at the present day to inter-tropical regions, comprising in them India and the Asiatic islands of Australia. Some are peculiar to the Mediterranean region. The aquatic plants, which form almost one-third of the flora, belong to genera now peculiar to the temperate regions of Europe and of North America, or occurring everywhere. The Miocene species belong to genera, of which several are found in India, tropical America, and the other inter-tropical regions, but which for the most part inhabit the sub-tropical and temperate regions, including the United States. Some of the genera are peculiar to the temperate regions. The aquatic genera, poor in species, occur everywhere, or else solely in the temperate regions. The Pliocene species belong to genera which almost all inhabit the temperate regions, either of the old continent or of the United States. A few only are of genera existing in India, Japan, and the north of Africa. These various floras, which present successively the character of those of inter-tropical, sub-tropical, and temperate regions, seem to indicate that central Europe has, since the commencement of the Tertiary period, been subjected, during the succession of time, to the influence of these three different temperatures. It would appear, then, Raulin remarks, that the climate of Europe has during the Tertiary period gradually become more temperate.

Brown coal occurs in the upper Tertiary beds, and in it vegetable structure is easily seen under the microscope. Goeppert, on examining the brown coal deposits of northern Germany and the Rhine, finds that Coniferæ predominate in a remarkable degree; among 300 specimens of bituminous wood collected in the Silesian brown coal deposits alone, only a very few other kinds of Exogenous wood occur. This seems remarkable, inasmuch as in the clays of the brown coal formation in many other places leaves of deciduous Dicotyledonous trees have been found; and yet the stems on which we may suppose them to have grown are wanting. The leaves have been floated away from the place where they grew by a current of water which was not powerful enough to transport the stems. The coniferous plants of these brown coal deposits belong to Taxineæ and Cupressineæ chiefly; among the plants are Pinites protolarix and Taxites Ayckii. Many of the Coniferæ exhibit highly compressed, very narrow annual rings, such as occur in Coniferæ of northern latitudes. Goeppert has described a trunk, or rather the lower end of a trunk, of Pinites protolarix, discovered in 1849 in the brown coal of Laasan in Silesia. It was found in a nearly perpendicular position, and measured more than 32 feet in circumference. Sixteen vast roots ran out almost at right angles from the base of the trunk, of which about four feet stood up perfect in form, but stripped of bark. Unfortunately the interior of the stem was almost entirely filled with structureless brown coal, so that only two cross sections could be obtained from the outer parts, one sixteen inches, the other three feet six inches broad. In the first section Goeppert counted 700, in the second 1300 rings of wood, so that for the half-diameter of 5½ feet, at least 2200 rings must have existed. As there is every reason to believe that the rings were formed in earlier ages just as the annual zones are now, this tree would be from 2200 to 2500 years old. Exogenous stems in lignite are often of great size and age. In a trunk near Bonn, Nöggerath counted 792 annual rings. In the turf bogs of the Somme, at Yseux near Abbeville, a trunk of an oak-tree has been found above 14 feet in diameter.

_GENERAL CONCLUSIONS._

We have thus seen that the vegetation of the globe is represented by numerous distinct floras connected with the different periods of its history, and that the farther back we go, the more are the plants different from those of the present day. There can be no doubt that there have been successive deposits of stratified rocks, and successive creations of living beings. We see that animals and plants have gone through their different phases of existence, and that their remains in all stages of growth and decay have been imbedded in rocks superimposed upon each other in regular succession. It is impossible to conceive that these were the result of changes produced within the limits of a few days. Considering the depth of stratification, and the condition and nature of the living beings found in the strata at various depths, we must conclude (unless our senses are mocked by the phenomena presented to our view) that vast periods have elapsed since the Creator in the beginning created the heavens and the earth. How far it may be possible in the future to correlate the history of the earth inscribed on its rocky tablets and deciphered by the geologist, and that short narrative which forms the introduction to the Sacred Volume, it is too difficult to say. At present there are no satisfactory materials for such a correlation; but one thing is certain, that both Revelation and Geology testify with one voice to the work of a Divine Creator.

"Who shall declare (Hugh Miller remarks) what through long ages the history of creation has been? We see at wide intervals the mere fragments of successive Floras; but know not how, what seem the blank interspaces, were filled; or how, as extinction overtook in succession one tribe of existences after another, and species, like individuals, yielded to the great law of death, yet other species were brought to the birth, and ushered upon the scene, and the chain of being was maintained unbroken. We see only detached bits of that green web which has covered our earth ever since the dry land first appeared. But the web itself seems to have been continuous throughout all time; though, as breadth after breadth issued from the creative loom, the pattern was altered, and the sculpturesque and graceful forms that illustrated its first beginnings and its middle spaces have yielded to flowers of richer colour and blow, and fruits of fairer shade and outline; and for gigantic club-mosses stretching forth their hirsute arms, goodly trees of the Lord have expanded their great boughs; and for the barren fern and the calamite clustering in thickets beside the waters, or spreading on flowerless hill-slopes, luxuriant orchards have yielded their ruddy flush, and rich harvests their golden gleam."

When we find animals and plants, of forms unknown at the present day, in all stages of development, we read a lesson as to the history of the earth's former state as conclusive as that which is derived from the Nineveh relics (independent of Revelation) in regard to the history of the human race. There is no want of harmony between Scripture and Geology. The Word and the Works of God must be in unison, and the more we truly study both, the more they will be found to be in accordance. Any apparent want of correspondence proceeds either from imperfect interpretation of Scripture or from incomplete knowledge of science. The changes in the globe have all preceded man's appearance on the scene. He is the characteristic of the present epoch, and he knows by Revelation that the world is to undergo a further transformation, when the elements shall melt with fervent heat, and when all the present state of things shall be dissolved, ere the ushering in of a new earth, wherein righteousness is to dwell.

_RECAPITULATION._

Recapitulation of the chief points connected with Fossil Botany:--

1. The vegetation of the globe has varied at different epochs of the earth's history.

2. The farther we recede in geological history from the present day, the greater is the difference between the fossil plants and those which now occupy the surface.

3. All fossil plants may be referred to the great classes of plants of the present day, Acotyledons, Monocotyledons, and Dicotyledons.

4. The fossil species are different from those of the present flora, and it is only when we reach the Tertiary periods that we meet with some genera which are without doubt identical.

5. Fossil plants are preserved in various conditions, according to the nature of their structure, and the mode in which they have been acted upon. Sometimes mere casts of the plants are found, at other times they are carbonised and converted into coal, while at other times, besides being carbonised, they are infiltrated with calcareous or siliceous matter, and finally, they may be petrified.

6. Cellular plants, and the cellular portions of vascular plants, have rarely been preserved, while woody species, and especially Ferns, which are very indestructible, have retained their forms in many instances.

7. In some cases, especially when silicified or charred, the structure of the woody stems can be easily seen in thin sections under the microscope.

8. The determination of fossil plants is a matter of great difficulty, and requires a thorough knowledge of structure, and of the markings on stems, roots, etc.

9. The rocks containing organic remains are called fossiliferous, and are divided into Primary, Secondary, and Tertiary, or into Palæozoic, Mesozoic, and Cainozoic, each of these series being characterised by a peculiar facies of vegetable life.

10. The mere absence of organic remains will not always be a correct guide as to the state of the globe.

11. The number of fossil species has been estimated at between 3000 and 4000; but many parts of plants are described as separate species, and even genera, and hence the number is perhaps greater than it ought to be.

12. Brongniart divides the fossil flora into three great epochs:--1. The reign of Acrogens; 2. The reign of Gymnosperms; 3. The reign of Angiosperms.

13. The reign of Acrogens embraces the Silurian, Carboniferous, and Permian epochs, in which there was a predominance of plants belonging to the natural orders Filices, Lycopodiaceæ, and Equisetaceæ, associated, however, with others of a higher class.

14. The reign of Gymnosperms embraces the lower and middle Secondary periods, and is characterised by the presence of numerous Coniferæ and Cycadaceæ.

15. The reign of Angiosperms includes the Cretaceous and Tertiary periods, and is marked by the predominance of Angiospermous Dicotyledons.

16. Coal is a vague term, referring to all kinds of fuel formed from the chemically-altered remains of plants.

17. When there is a great admixture of mineral matter, so that it will not burn as fuel, then a shale is produced.

18. The microscopic structure of Coal probably varies according to the nature of the plants of which it is composed, and the changes produced by pressure, heat, and other causes. Cellular tissue, punctated woody tissue, and scalariform vessels, have been detected in it.

19. Certain temporary and local floras seem to have given origin to peculiar layers of coal.

20. During the Carboniferous epoch we meet with Ferns, Sigillarias, and their roots called Stigmarias, Lepidodendrons, Ulodendrons, Calamites, Gymnosperms, etc.

21. The plants forming coal have grown in the basin where the coal is found; but sandstone rocks in the coal-measures deposited by water having a considerable velocity, and consequently carrying power, contain sometimes trunks of large trees which have been drifted like snags.

22. The strata between the Permian epoch and Chalk display numerous Gymnosperms, especially belonging to the Cycadaceous Order. Some of them exhibit limited coal deposits.

23. The Chalk and Tertiary strata display not only Acrogens and Gymnosperms, but also Angiospermous Dicotyledons, some of which, at the Miocene period, belong apparently to genera of the present day.

24. Brown Coal occurs in the Upper Tertiary beds, and in it vegetable structure is easily seen under the microscope.

25. Raulin thinks that during the Tertiary epoch the flora of Europe has gradually assumed a more temperate character.

26. The Eocene flora, according to Unger, resembled in many respects that of Australia at the present day.

27. The Miocene flora is characterised by a number of exotic forms of warm regions with those of temperate climates. It is largely seen in the Arctic Regions.

28. The Pliocene flora has great analogy with that of the temperate regions of Europe, North America, and Japan.

_WORKS ON FOSSIL BOTANY._

On the subject of Fossil Botany the following works may be consulted:--

Abhandlungen der Kaiserlich Königlichen Geologischen Reichsanstalt, Band. ii. Wien. 1855.

Argyll, Duke of, on Tertiary Leaf-Beds in the Isle of Mull, Journ. Geol. Soc. Lond., vii. May 1851.

Balfour, J. H., on certain Vegetable Organisms in Coal from Fordel, Trans. R.S.E., vol. xxi. p. 187.

Baily, W. H., Figures of Characteristic British Fossils, 1871-2.

Bennett, J. Hughes, on the Structure of Torbane Hill Mineral and other Coals, Trans. R. Soc. Ed., vol. xxi. p. 173.

Binney, E. W., on Calamites and Calamodendron, Palæontographical Society's Memoirs, 1868.

---- on the Structure of Fossil Plants found in the Carboniferous Strata. Palæontographical Society's Memoirs, 1871.

---- Description of some Fossil Plants, showing Structure in the Lower Coal Seam of Lancaster and Yorkshire, Phil. Trans., vol. 155, p. 579.

Bowerbank, Fossil Fruits and Seeds of the London Clay.

Brongniart, Histoire des Végétaux Fossiles, 1828-44.

---- Observations sur la Structure intérieure du Sigillaria, etc., in Archives du Museum, i. 405.

---- Exposition Chronologique des Périodes de Végétation, in Ann. des Sc. Nat. 3d series, Bot. xi. 285.