Introduction to the Study of Palæontological Botany

FOSSIL FLORA OF THE TERTIARY OR CAINOZOIC PERIOD,

(INCLUDING THE CRETACEOUS EPOCH).

Reign of Angiosperms.

This reign is characterised by the appearance of Angiospermous Dicotyledons, plants which constitute more than three-fourths of the species of the existing flowering plants of the globe, and which appear to have acquired the predominance from the commencement of the Tertiary epoch. They are plants with seeds contained in seed-vessels, and each seed with two cotyledons. These plants, however, appear even at the beginning of the Cretaceous period. In this reign, therefore, Brongniart includes the upper Secondary period, or the Cretaceous system, and all the Tertiary period. The Cretaceous may be considered as a sort of transition period between the reign of Gymnosperms and Angiosperms.

Flora of the Chalk.

The Chalk flora is characterised by the Gymnospermous almost equalling the Angiospermous Dicotyledons, and by the existence of a considerable number of Cycadaceæ, which do not appear in the Tertiary period. The genus Credneria is one of the characteristic forms. In this period we find Algæ represented by Cystoseirites, Confervites, Sargassites, and Chondrites; Ferns by peculiar species of Pecopteris and Protopteris; Naiadaceæ by Zosterites; Palms, by Flabellaria and Palmacites; Cycadaceæ by Cycadites, Zamites, Microzamia, Fittonia, and Bennettites; Coniferæ, by Brachyphyllum, Widdringtonites, Cryptomeria, Abietites, Pinites, Cunninghamites, Dammarites, Araucarites; and Angiospermous Dicotyledons, by Comptonites, Alnites, Carpinites, Salicites, Acerites, Juglandites, and Credneria. At the base of the Tertiary period there are deposits of Algæ of a very peculiar form, belonging to the genera Chondrites and Munsteria. No land plants have been found mingled with these marine species.

In the Gault, near Folkestone, an interesting association of coniferous fruits has been found, consisting of two species of Sequoia, along with two of Pinus. The pines belong to the same group as those which now grow with the Wellingtonias in California, showing the remarkable fact that the coniferous vegetation of the high lands of the Upper Cretaceous period had a facies similar to that now existing in the mountains on the west of North America. We figure both the species of Sequoiites—viz. S. ovalis (Fig. 91), a large cone, and S. Gardneri (Plate II. Fig. 7). In the present day there are two species of the genus Sequoia—viz. S. gigantea (Wellingtonia gigantea) and S. sempervirens.[20] In the Lower Greensand a remarkably fine cone belonging to the same group as the Cedar has been found. This is the Pinites Leckenbyi (Plate II. Fig. 4). A section exhibits the seeds in their true position, some of which are preserved so as to exhibit the form and position of the embryo.

The Tertiary period is characterised by the abundance of Angiospermous Dicotyledons and of Monocotyledons, more especially of Palms. By this it is distinguished from the more ancient periods. Angiosperms at this period greatly exceed Gymnosperms. Cycadaceæ are very rare, if not completely wanting, in the European Tertiary strata, and the Coniferæ belong to genera of the temperate regions. In the lower Tertiaries Carruthers has found a fossil Osmunda, and the existence of a group of Pines having cones with a very thick apophysis. From their remarkable external aspect, these cones had been considered to be Cycadean, but their internal structure indicates that they are coniferous. Pinites ovatus is one of these cones (Fig. 92). The Cupressineæ are found in the Tertiary beds only. Taxodieæ are represented by Sequoiites (Plate II. Fig. 7) in the Cretaceous and Eocene strata. Peuce australis of Van Diemen's Land and P. Pritchardi of Ireland are Tertiary plants. The Peuce of Eigg (P. Eggensis), according to Geikie, is also Tertiary, and not Oolitic. Isoetes is mentioned by Schimper as a Tertiary genus. Although the vegetation throughout the whole of the Tertiary period presents pretty uniform characters, still there are notable differences in the generic and specific forms, and in the predominance of certain orders at different epochs. Brongniart does not entirely agree with Unger as to these epochs. Many of the formations classified by Unger in the Miocene division he refers with Raulin to the Pliocene. He divides the Tertiary period, as regards plants, into the Eocene, Miocene, and Pliocene epochs, and gives the following comparative results from an examination of their floras:—

Flora of the Eocene Epoch.

In the Eocene formation the fossil fruits of the Isle of Sheppey increase the number of Phanerogamous plants, only a small proportion of which have as yet been described. This is an exceptional locality, and the deposit in which the fruits occur is probably the silt found at the mouth of a large river which flowed, like the Nile, from tropical regions towards the north. The number of plants as given by Brongniart is much smaller than that mentioned by Unger (p. 23). The latter includes in his enumeration a considerable amount of uncertain species.

The Eocene epoch in general is characterised by the predominance of Algæ and marine Naiadaceæ, such as Caulinites and Zosterites; by numerous Coniferæ, the greater part resembling existing genera among the Cupressineæ, and appearing in the form of Juniperites, Thuites, Cupressinites (Plate II. Figs. 8, 9), Callitrites, Frenelites, and Solenostrobus; by the existence of a number of extra-European forms, especially of fruits, such as Nipadites, Leguminosites, Cucumites, and Hightea; and by the presence of some large species of Palm belonging to the genera Flabellaria and Palmacites (Fig. 93).

Unger says that the Eocene flora has resembled in many respects that of the present Australian vegetation. He gives the following genera as occurring at the Eocene epoch:—Araucaria, Podocarpus, Libocedrus, Callitris, Casuarina, Pterocarpus, Drepanocarpus, Centrolobium, Dalbergia, Cassia, Cæsalpinia, Bauhinia, Copaifera, Entada, Acacia, Mimosa, Inga. (Seemann's Journal of Bot. vol. iii. p. 43.) Amber is considered to be the produce of many Coniferæ of this epoch, such as Peuce succinifera or Pinites succinifera, and Pinus Rinkianus. It occurs in East Prussia in great quantity, and it is said that many pieces of fossil wood occur there, which, when moderately heated, give out a decided smell of amber. Connected with these beds are found cones belonging to Pinites sylvestrina and P. Pumilio-miocena, species nearly allied to the living species; others to Pinites Thomasianus and P. brachylepis. Goeppert contrasts the present flora of Germany and that of the Amber epoch as follows:—

(See remarks by Goeppert on the Amber Flora, etc., Edin. N. Phil. Journ. lvi. 368; and Quart. Journ. Geol. Soc. x. 37.) In the lower Eocene of Herne Bay, Carruthers noticed a fern like Osmunda (Fig. 94), which he calls Osmundites Dowkeri (Plate I. Figs. 8, 9). This specimen was silicified; starch grains contained in its cells, and the mycelium of a parasitic fungus traversing some of them, were perfectly preserved. Berkeley has detected in amber fossil fungi, which he has named Penicillium curtipes, Brachycladium Thomasinum, and Streptothrix spiralis.[21] Some Characeæ are also met with, as Chara medicaginula and C. prisca, with a fossil called Gyrogonites, the nucule or the fructification of these plants. Carpolithes ovatus, a minute seed-vessel, occurs in the Eocene beds of Lewisham. Another small fruit, of a similar nature, called Folliculites minutulus, occurs in the Bovey Tracey coal, which belongs to the Tertiary beds.

Flora of the Miocene Epoch.

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.

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:—

Works on Fossil Botany.

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

EXPLANATION OF PLATES.

PLATE I.