FOSSIL FLORA OF THE SECONDARY OR MESOZOIC PERIOD.

Reign of Gymnosperms.

Fig. 57. Fig. 59.
Fig. 58. Fig. 60.
Fig. 57. Pinus sylvestris, Scotch Fir.
Fig. 58. Abies excelsa, common Spruce Fir of northern Europe.
Fig. 59. Larix Europæa, the Larch, indigenous on the Alps of middle Europe.
Fig. 60. Cedrus Libani, Cedar of Lebanon.

 

The Gymnospermous plants of the present day are included in two natural orders, Coniferæ and Cycadaceæ. Under Coniferæ are enumerated the various species of Pine (Fig. 57), Spruce (Fig. 58), Larch (Fig. 59), Cedar (Fig. 60), Eutassa, Araucaria (Fig. 61), Sequoia, Cryptomeria, Taxodium, Cypress, Juniper (Fig. 70), Salisburia, Dacrydium, Yew (Fig. 71), etc.

Fig. 61. Fig. 65.
Fig. 62. Fig. 63. Fig. 64.
Fig. 61. Araucaria excelsa, called also Altingia or Eutassa or Eutacta excelsa, Norfolk Island Pine.
Fig. 62. Woody tubes of fir, with single rows of discs.
Fig. 63. Woody tubes of fir, with double rows of discs, which are opposite to each other.
Fig. 64. Woody tubes of Araucaria excelsa, with double and triple rows of discs, which are alternate.
Fig. 65. Longitudinal section of the stem of a Gymnosperm, showing tubes of wood marked with punctations in one or more rows, and a medullary ray composed of cells running across the pleurenchyma.
Fig. 66. Fig. 68. Fig. 69.
Fig. 66. Linear leaves of Pinus Strobus, Weymouth Pine, in a cluster of five, with scaly sheath at the base.
Fig. 67. Cone of Pinus sylvestris, Scotch Fir.
Fig. 68. Cone of Cupressus sempervirens, common Cypress.
Fig. 69. Scale, s, of mature cone of Pinus sylvestris, with two naked winged seeds, m m, at its base; ch marks the chalaza, m the micropyle.

 

The Coniferæ of the present day are distinguished as resinous trees or shrubs with punctated woody tissue (Figs. 62, 63, 64, 65), linear acerose or lanceolate parallel-veined leaves, sometimes clustered, and having a membranous sheath at the base (Fig. 66). Male flowers in deciduous catkins; female flowers in cones (Figs. 67, 68). The seeds are considered by most botanists as being naked, i.e. not contained in a true pistil (Fig. 69). Some of the conifers have a succulent cone, as the juniper (Fig. 70), and the yew (Figs. 71-73) has a succulent mass covering a single naked seed (Fig. 73). The yew also has its pleurenchyma marked both with punctations and spiral fibres. The arrangement of the punctations in the Coniferæ gives characters which enable us to classify the woods into groups that have some relation to the genera established from the reproductive organs (see Figs. 62-65).

Fig. 70. Fig. 71. Fig. 73.
Fig. 70. Fruiting branch of Juniperus communis, common Juniper, with linear acerose leaves and succulent cones.
Fig. 71. Branch of Taxus baccata, common Yew.
Fig. 72. Male flower of Yew, with bracts at the base.
Fig. 73. Fruit of Yew, consisting of a single naked seed partially covered by a succulent receptacle.

 

The natural order Cycadaceæ is not so largely represented at the present day as it was during the Mesozoic epoch. Among the genera of the present day are Cycas (Fig. 74), Zamia, Macrozamia, Encephalartos (Fig. 75), Dion, Stangeria, etc. They are small palm-like trees or shrubs, with unbranched stems, occasionally dichotomous, marked with leaf-scars, and having large medullary rays along with pitted woody tissue. The leaves are pinnate, except in Bowenia, which has a bipinnate leaf. Males in cones. Females consisting of naked ovules on the edges of altered leaves, or on the inferior surface of the peltate apex of scales.[18]

Flora of the Trias and Lias Epochs.

Fig. 74. Fig. 75.
Fig. 74. Cycas revoluta, one of the false Sago-plants found in Japan.
Fig. 75. Encephalartos (Zamia) pungens, another starch-yielding Cycad.

 

In this reign the Acrogenous species are less numerous; the Gymnosperms almost equal them in number, and ordinarily surpass them in frequency. There are two periods in this reign, one in which Coniferæ predominate, while Cycadaceæ scarcely appear; and another in which the latter family preponderates as regards the number of species, and the frequency and variety of generic forms. Cycadaceæ occupied a more important place in the ancient than in the present vegetable world. They extend more or less from the Trias formation up to the Tertiary. They are rare in the Grès bigarré or lower strata of the Triassic system. They attain their maximum in the Lias and Oolite, in each of which upwards of 40 species have been enumerated, and they disappear in the Tertiary formations. Schimper describes 13 genera of fossil Zamiæ, and about 20 Cycadeæ. He thinks that Trigonocarpum (15 species), Rhabdocarpum (24 species), Cardiocarpum (21 species), and Carpolithes (9 species), are all fruits of Cycadeæ. Many supposed fossil Cycads are looked upon by Carruthers as Coniferæ. Zamia macrocephala, or Zamites macrocephalus, or Zamiostrobus macrocephalus, is called by him Pinites macrocephalus; Zamia ovata, or Zamites ovatus, or Zamiostrobus ovatus, is Pinites ovatus; Zamia Sussexiensis is Pinites Sussexiensis. Among other species of Pinites noticed by Carruthers are Pinites oblongus, P. Benstedi, P. Dunkeri, P. Mantellii, P. patens, P. Fittoni, P. elongatus. It is important to notice that in an existing Cycad called Stangeria paradoxa the veins of the pinnæ rise from a true midrib and fork, characters which render untenable the distinction usually relied upon between the foliage of Ferns and Cycads.

Fig. 76.
Fig. 76. Schizoneura heterophylla, one of the fossil Coniferæ of the Triassic system.

In Brongniart's Vosgesian period, the Grès bigarré, or the Red Sandstones and Conglomerates of the Triassic system, there is a change in the flora. Sigillarias and Lepidodendrons disappear, and in their place we meet with Gymnosperms, belonging to the genera Voltzia, Haidingera, Zamites, Ctenis, Æthophyllum, and Schizoneura (Fig. 76). The genus Voltzia is confined to the Trias, and though a true conifer, it is not easy to correlate it with any living form. It is apparently Abietineous, having two seeds to each scale, but they are placed on the dilated upper portion of the scale. The leaves are of two kinds, the one broad and short, and the other at the tops of the branches long and linear. Species of Neuropteris, Pecopteris, and other acrogenous coal genera are still found, along with species of Anomopteris and Crematopteris—peculiar Fern-forms, which are not found in later formations. Stems of arborescent Ferns are more frequent than in the next period.

Fig. 77.

The Jurassic period of Brongniart embraces the Keupric period or variegated marls of the Triassic system, the Liassic epoch, the Oolitic and the Wealden. The flora of the Keupric epoch differs from that of the Grès bigarré of the Vosges. The Acrogens are changed as regards species, and frequently in their genera. Thus we have the genera Camptopteris, Sagenopteris, and Equisetum. Among Gymnosperms, the genera Pterophyllum and Taxodites occur.

Fig. 78. Fig. 79.
Figs. 77 to 81. Cycadaceæ of the Jurassic epoch of Brongniart, and of the Oolite. Fig. 77. Zamites, one of the fossil Cycadaceæ. Fig. 78. Pterophyllum Pleiningerii, leaf of a fossil Cycad. Fig. 79. Nilssonia compta (Pterophyllum comptum of Lindley and Hutton), from the Oolite of Scarborough. Lower part of the pinnatifid leaf, with blunt almost square divisions. There are numerous veins, slightly varying in thickness; while in Pterophyllum there are numerous veins of equal thickness, in Cycadites there is a solitary vein forming a thick midrib. Fig. 80. Palæozamia pectinata (Zamia pectinata of Brongniart, and Lindley and Hutton), a pinnated leaf, with a slender rachis. The pinnæ are linear, somewhat obtuse, with slender equal ribs. It is found in the Oolite of Stonesfield (Lindley and Hutton).
Fig. 80.

 

In the Lias the essential characters of the flora are the predominance of Cycadaceæ, in the form of species of Cycadites, Otozamites, Zamites (Fig. 77), Ctenis, Pterophyllum (Fig. 78), and Nilssonia (Fig. 79), Palæozamia (Fig. 80), and the existence among the Ferns of many genera with reticulated venation, such as Camptopteris and Thaumatopteris, some of which began to appear at the Keupric epoch. Coniferous genera, as Brachyphyllum (Fig. 81), Taxodites, Palissya, and Peuce, are found. In the Lias near Cromarty, Miller states that he found a cone with long bracts like those of Pinus bracteata.

Flora of the Oolitic Epoch.

In the Oolitic epoch the flora consists of numerous Cycadaceæ and Coniferæ, some of them having peculiar forms. Its distinctive characters are, the rarity of Ferns with reticulated venation, which are so numerous in the Lias, the frequency of the Cycadaceous genera Otozamites and Zamites, which are most analogous to those now existing; the occurrence of a remarkable group presenting very anomalous structure in their organs of reproduction, to which Carruthers has given the name of Williamsonia; and the diminution of Ctenis, Pterophyllum, Palæozamia, and Nilssonia, genera far removed from the living kinds; and lastly, the greater frequency of the coniferous genera, Brachyphyllum and Thuites, which are much more rare in the Lias. In the Scottish Oolite at Helmsdale, Miller detected about 60 species of plants, including Cycadaceæ and Coniferæ, with detached cones, and Fern-forms resembling Scolopendrium. He also discovered a species of Equisetum, and what he supposed to be a Calamite.

Fig. 81. Fig. 82.
Fig. 81. Brachyphyllum mammillare, a Coniferous plant of the Oolitic system, Yorkshire.
Fig. 82. Equisetum columnare, a fossil species of the Oolite of Yorkshire.
Fig.83. Fig. 85.
Fig. 83. Araucarites sphærocarpus, Carr., found in the inferior Oolite at Bruton, Somersetshire.
Fig. 84. Termination of a scale of Araucarites sphærocarpus, Carr.
Fig. 85. Section of a scale of Araucarites sphærocarpus, Carr., showing the size and position of the seed.
Fig. 86. Fig. 87.
Fig. 86. The Dirt-bed of the Island of Portland, containing stumps of fossil Cycadaceæ in an erect position.
Fig. 87. Cycadoidea megalophylla (Mantellia nidiformis of Brongniart), a subglobose depressed trunk, with a concave apex, and with the remains of the petioles disposed in a spiral manner, the markings being transversely elliptical. It is found in the Oolite of the Island of Portland, in a silicified state.

 

There is an absence of true coal-fields in the secondary formations generally; but in some of the Oolitic series, as in the lower Oolite at Brora, in Sutherlandshire, and in the north-east of Yorkshire, and the Kimmeridge clay of the upper Oolite, near Weymouth, there are considerable deposits of carbonaceous matter, sometimes forming seams of coal which have been worked for economic purposes.[19] Some suppose that the Brora coal was formed chiefly by Equisetum columnare (Fig. 82). In the sandstones and shales of the Oolitic series, especially in the lower Oolite of the north of England, as at Whitby and Scarborough, as well as in Stonesfield slate, the Portland Crag of the middle, and the Portland beds of the upper Oolite, numerous fossil plants are found. Peuce Lindleyana is one of the Coniferæ of the lower Oolite. Beania (Plate II. Fig. 2) is a Cycadaceous fossil from the Oolite of Yorkshire (Carruthers, Geol. Mag. vi. 91). Araucarites sphærocarpus (Figs. 83, 84, 85) is found in the inferior Oolite, and separate scales of Araucarian fruits occur in the Oolitic shales of Yorkshire (Araucarites Phillipsii, Plate II. Fig. 11), and in the "slate" at Stonesfield (A. Brodiei, Plate II. Fig. 10). The upper Oolite at Portland contains an interesting bed, about a foot in thickness, of a dark brown substance. This is the Dirt-bed (Fig. 86) made up of black loam, which, during the Purbeck period, formed a surface soil which was penetrated by the roots of trees, fragments of whose stems are now found in it fossilised. These consist of an assemblage of silicified stumps or stools of large trees, from 1-3 feet high, standing in their original position, with the roots remaining attached to them, and still penetrating the earth in which they grew. Besides the erect trunks many stems have been broken and thrown down, and are buried in a horizontal position in the bed. They belong to Coniferæ and Cycadaceæ. One of these is Mantellia nidiformis, shown in Fig. 87. Carpolithes conicus and C. Bucklandi are fruits found in the Oolite. Some look upon them as fruits of palms.

Fig. 88. Fig. 89.
Fig. 88. Kaidacarpum ooliticum, Carr., fruit of a fossil allied to Pandanaceæ, from the great Oolite near Northampton.
Fig. 89. Pandanus odoratissimus, Screw-pine, with adventitious roots.

 

Several species of Pandanaceous fruits have been found in Oolitic strata. Buckland described one of them as Podocarya, which is remarkable, as it consists of a single but many-seeded drupe. To another form, more nearly allied to the existing plants, Carruthers has given the name Kaidacarpum, and has described three species. These fruits are made up of a large number of single-seeded drupes. The species figured (Fig. 88) is from the great Oolite, near Northampton. In Fig. 89 a representation is given of one of the Pandanaceæ, the screw-pines of the present day.

Flora of the Wealden Epoch.

Fig. 90.
Fig. 90. Fossil Wood, Abietites Linkii. A Coniferous plant from the Wealden, showing punctated woody tissue and medullary rays.

The flora of the Wealden epoch is characterised in the south of England by the abundance of the fern called Lonchopteris Mantellii, and in Germany by the predominance of the Conifer denominated Abietites Linkii (Fig. 90), and the presence of Araucarites Pippingfordensis, as well as by numerous Cycadaceæ, such as species of Cycadites, Zamites, Pterophyllum, Mantellia, Bucklandia, and a remarkable genus having a fleshy fruit, and related to the ordinary Cycadaceæ as Taxus is to the other Coniferæ, which has been fully described in the Linn. Trans., under the name of Bennettites (Plate II. Fig. 3). In the Wealden at Brook Point, Isle of Wight, Cycads have been detected allied to Encephalartos. The fruits of them are described by Carruthers as Cycadeostrobus. He describes the following species:—Cycadeostrobus ovatus (Plate II. Fig. 1), C. truncatus, C. tumidus, C. elegans, C. Walkeri, C. sphæricus, in the Oxford clay of Wiltshire; C. primævus in the inferior Oolite at Burcott Wood and Livingston, and C. Brunonis. Mantell states that he has found 40 or 50 fossil cones in the Wealden of England; they belong either to the genus Cycadeostrobus or to the pines mentioned below as occurring in the Wealden. The Wealden fresh-water formation terminates the reign of Gymnosperms. Carruthers gives the following list of the remains of Coniferæ which have been found in the secondary strata of Britain, excluding the Trias:—

Upper Chalk.—Wood in flint nodules.

Upper Greensand.—Foliage and cone of Sequoiites Woodwardii; cone of Pinites oblongus.

Gault.—Cones of Pinites gracilis and P. hexagonus, Sequoiites Gardneri and S. ovalis.

Lower Greensand.—Water-worn and bored pieces of wood; cones of Pinites Benstedi, P. Sussexiensis, and P. Leckenbyi.

Wealden.—Driftwood, foliage of Abietites Linkii; cones of Pinites Dunkeri, P. Mantellii, P. patens, and P. Fittoni, and of Araucaria Pippingfordensis; foliage (and drupes?) of Thuites Kurrianus.

Purbeck.—Fossil forest in situ at Isle of Portland; cone "nearly related to Araucaria excelsa" in the Dirt-bed.

Portland Stone.—Driftwood Araucarites.

Kimmeridge Clay.—Cone of Pinites depressus.

Oxford Clay.—Driftwood and foliage of Araucarites.

Great Oolite.—Driftwood of Araucarites; foliage of Thuites acutifolius, T. articulatus, T. cupressiformis, T. divaricatus, and T. expansus, and of Taxites podocarpoides; detached cones at Helmsdale, Sutherland.

Inferior Oolite.—Wood of Peuce Eggensis (Tertiary according to Geikie); foliage of Brachyphyllum mammillare, Cryptomerites? divaricatus, and Palissya? Williamsonis; cones of Araucarites sphærocarpus, A. Brodiei, and A. Phillipsii. Pinites primæva (Lindl. and Hutt.) is a Cycadean fruit.

Lias.—Wood of Pinites Huttonianus and P. Lindleyanus; foliage of Araucaria peregrina and Cupressus latifolia; cone of Pinites elongatus, and "cone with long bracts like those of Pinus bracteata," from Cromarty.

Carruthers gives the following arrangement of fossil Cycadaceæ in the Transactions of the Linn. Soc. vol. xxvi.—Firstly, the Cycadeæ: including the genus Bucklandia, Presl; and species B. anomala, B. Mantellii, B. squamosa, B. Milleriana—the two first-named species being from the Wealden, and the two last-named from the Oolite. Secondly, the Zamieæ: including the genus Yatesia, Carr.; and species Y. Morrisi, Lower Cretaceous; Y. gracilis, Lias; Y. crassa, M. Oolite; Y. Joassiana, M. Oolite; the genus Fittonia, Carr., and species F. squamata, U. Cretaceous; the genus Crossozamia, Pomel, and species C. Moreaui, Pomel, Jurassic, and C. Buvignieri, Pomel, Jurassic—both from St. Michel, France. Thirdly, the Williamsonieæ: including the genus Williamsonia, Carr.; and species W. gigas, W. pecten, W. hastula, all from the inferior Oolite. Fourthly, the Bennettiteæ: including the genus Bennettites, Carr., and species B. Saxbyanus, Wealden; B. Gibsonianus, Lr. Greensand; B. maximus, Wealden; B. Portlandicus, Lr. Purbeck; and B. Peachianus, M. Oolite; the genus Mantellia, Brong., and species M. nidiformis, M. intermedia, M. microphylla, from the Lr. Purbeck; and M. inclusa, from the Lr. Cretaceous; the genus Raumeria, Goeppert, and species R. Reichenbachiana, from Galicia, and R. Schulziana from Silesia.