Chapter 9

[CX]See “Memoirs of Dr. Williamson,” in “Philosophical Transactions,” for ample details.

As a type of Lepidodendron, I may describe one of the oldest Carboniferous species characteristic of the Lower Carboniferous in America, and corresponding toL. Veltheimianumof Europe.

Lepidodendron Corrugatum, Dawson.—(SeeFig. 43,supra.) “Quarterly Journal of Geological Society,” vol. xv.; “Acadian Geology,” page 451.

Habit of Growth.—Somewhat slender, with long branches and long, slender leaves having a tendency to become horizontal or drooping.

Markings of Stem.—Leaf-bases disposed in quincunx or spirally, elongate, ovate, acute at both ends, but more acute and slightly oblique at the lower end; most prominent in the upper third, and with a slight vertical ridge. Leaf-scars small, rounded, and showing only a single punctiform vascular scar. The leaf-scar on the outer surface is in the upper third of the base; but the obliquity of the vascular bundle causes it to be nearly central on the inside of the epidermis. In young succulent shoots the leaf-scars are contiguous and round as in Cyclostigma, without distinct leaf-bases. In this state it closely resemblesL. Olivieri, Eichwald.[CY]

[CY]Lethæa Rossica, Plate Y, Figs. 12, 13.

In the ordinary young branches the leaf-scars are contiguous, and closely resemble those ofL. elegans, Brongt. (Fig. 43 C). As the branches increase in diameter the leaf-scars slightly enlarge and sometimes assume a verticillate appearance (Fig. 43 D). As they still further enlarge they become separated by gradually increasing spaces of bark, marked with many waving striæ or wrinkles (Fig. 43 I, N). At the base of old stems the bark assumes a generally wrinkled appearance without distinct scars.

Knorria or Decorticated States.—Of these there is a great variety, depending on the state of preservation, and the particular longitudinal ridges.Fig. 43 Dshows a form in which the vascular bundles appear as cylindrical truncate projections. Other forms showthe leaf-bases prominent, or have an appearance of longitudinal ribbing produced by the expansion of the bark.

Structure of Stem.—This is not perfectly preserved in any of my specimens, but one flattened specimen shows a central medulla with a narrow ring of scalariform vessels surrounding it, and constituting the woody axis. The structure is thus similar to that ofL. Harcourtii, which I regard as probably the same with the closely allied European species L. Veltheimianum.

Leaves.—These are narrow, one-nerved, curving somewhat rapidly outward (Figs. 43, B, C, D). They vary from one to two inches in length.

Roots.—I have not seen these actually attached, but they occur very abundantly in the under-clays of some erect forests of these plants at Horton Bluff, and are of the character of Stigmariæ (Figs.30,31). In some of the under-clays the long, flattened rootlets are excessively abundant, and show the mark of a central vascular bundle.

Fructification.—Cones terminal, short, with many small, acute imbricate scales. Spore-cases globular, smooth (Fig. 43 C). On the surface of some shales and sandstones at Horton there are innumerable round spore-cases of this tree about the size of mustard-seed (Fig. 43 F). Large slabs are sometimes covered with these, and thin layers of shale are filled with flattened specimens.

This is the characteristic species of the Lower Carboniferous coal-measures, occurring in great profusion at Horton Bluff and its vicinity, also at Sneid’s Mills near Windsor, Noel and Five-Mile River, at Norton Creek and elsewhere in New Brunswick (Matthew’s collection), and at Antigonish (Honeyman’s collection).

I have received from the lowest Carboniferous beds of Ohio specimens of this species.[CZ]According to Rogers and Lesquereux similar forms occur in the Vespertine of Pennsylvania and in the Lower Carboniferous of Illinois.L. Veltheimianumof western Europe andL. glincanumof Russia are closely allied Lower Carboniferous species.[DA]

[CZ]“Journal of Geological Society,” November, 1862, p. 313.

[DA]For comparisons of these see “Report on Plants of Lower Carboniferous of Canada,” p. 21.

A very different type is furnished by a new species from the middle coal-formation of Clifton, New Brunswick.

Lepidodendron Cliftonense, Dawson.—Habit of Growth.—Robust, with thick branches, and leaves several inches in length. Terminal branches becoming slender, with shorter leaves.

Markings of Stem.—Leaf-bases long oval, pointed at ends, enlarging with growth of stem. Leaf-scars central, rhombic, transverse.

Leaves.—One-nerved, acutely pointed, from four inches in length on the larger branches to one inch or less on the branchlets.

Fructification.—Cones large, cylindrical or long oval, with large scales of trigonal form, and not elongated but lying close to the surface. Borne on lateral, slender branchlets, with short leaves.

GenusLepidophloios, Sternberg;Ulodendron, L. and H.;Lomatophloios, Corda.

Lepidophloios.—Under this generic name, established by Sternberg, I include those lycopodiaceous trees of the coal-measures which have thick branches, transversely elongated leaf-scars, each with three vascular points and placed on elevated or scale-like protuberances, long one-nerved leaves, and large lateral strobiles in vertical rows or spirally disposed. Their structure resembles that ofLepidodendron, consisting of aSternbergiapith, a slender axis of large scalariform vessels, giving off from its surface bundles of smaller vessels to the leaves, a very thick cellular bark, and a thin dense outer bark, having some elongated cells or bast-tissue on its inner side. In these trees the exogenous outer cylinder is less developed than in the Lepidodendra, and is sometimes wanting in stems or branches of some thickness.

RegardingL. laricinumof Sternberg as the type of the genus, and taking in connection with this the species described by Goldenberg, and my own observations on numerous specimens found in Nova Scotia, 1 have no doubt thatLomatophloios crassicaulisof Corda, and other species of that genus described by Goldenberg,UlodendronandBothrodendronof Lindley,Lepidodendron ornatissimumof Brongniart, andHalonia punctataof Geinitz, all belong to this genus, and differ from each other only in conditions of growth and preservation. Several of the species ofLepidostrobusandLepidophyllumalso belong toLepidophloios.

The species ofLepidophloiosare readily distinguished fromLepidodendronby the form of the areoles, and by the round scars on the stem, which usually mark the insertion of the large strobiles, though in barren stems they may also have produced branches; still, the fact of my finding the strobilesin situin one instance, the accurate resemblance which the scars bear to those left by the cones of the red pine when borne on thick branches, and the actual impressions of the radiating scales in some specimens, leave no doubt in mymind that they are usually the marks of cones; and the great size of the cones ofLepidophloiosaccords with this conclusion.

The species ofLepidophloiosare numerous, and individuals are quite abundant in the coal formation, especially toward its upper part. Their flattened bark is frequent in the coal-beds and their roofs, affording a thin layer of pure coal, which sometimes shows the peculiar laminated or scaly character of the bark when other characters are almost entirely obliterated. The leaves also are nearly as abundant as those of Sigillaria in the coal-shales. They can readily be distinguished by their strong, angular midrib.

The markings ofLepidophloiosmay easily be mistaken for those of theClathrariatype ofSigillaria. When the stem only is seen, they can be distinguished by the length of the leaf-bases inLepidophloios, and by the dominant central vascular scar; also by the one-nerved and ribbed leaves. Where the large, round marks of the cones are present, these are an infallible guide, never being present inSigillaria. As the cones grew on the upper sides of the branches, the impression of the lower side often shows no cone-scars, or only two lateral rows, whereas on the upper side of the same branch they appear spirally arranged. I may describe as an example—

Lepidophloios Acadianus, Dawson. Leaf-bases broadly rhombic, or in old stems regularly rhombic, prominent, ascending, terminated by very broad rhombic scars having a central point and two lateral obscure points. Outer bark laminated or scaly. Surface of inner bark with single points or depressions. Leaves long, linear, with a strong keel on one side, five inches or more in length. Cone-scars sparsely scattered on thick branches, either in two rows or spirally, both modes being sometimes seen on the same branch. Scalariform axis scarcely an inch in diameter in a stem five inches thick. Fruit, an ovate strobile with numerous acute scales covering small globular spore-cases. This species is closely allied toUlodendron majusandLepidophloios laricinus, and presents numerous varieties of marking. Coal-formation, Nova Scotia.

FamilyCalamiteæ;GenusCalamites, Suckow.

The plants of this genus are unquestionably allied to the modernEquisetaceæ, but excel these so much in variety of form and structure, and are so capricious in their states of preservation, and so liable to be mistaken for parts of plants generically different, that they have given rise to much controversy. The following considerations will enable us to arrive at some certainty.

The genusCalamiteswas originally founded in the longitudinallyribbed and jointed stems so frequent in the coal-formation, and of which the commonC. Suckoviiis a typical form. The most perfect of these stems represent the outer surface immediately within the epidermis, in which case transverse lines or constrictions mark the nodes, and at the nodes there are rounded spots, sometimes indicating radial processes of the pith, first described by Williamson; in other cases, the attachment of branchlets, or in some specimens both. But some specimens show the outer surface of the epidermis, in which case the transverse nodal lines are usually invisible, though the scars of branchlets may appear. In still other examples the whole of the outer tissues have perished, and the so-called Calamite is a cast of the interior of the stem, showing merely longitudinal ribbing and transverse nodal constrictions. In studying these plantsin situin the erect Calamite brakes of the coal-formation of Nova Scotia, one soon becomes familiar with these appearances, but they are evidently unknown to the majority of palæobotanists, though described in detail more than twenty years ago.

When the outer surface is preserved it is sometimes seen to bear verticils of long needle-like leaves (C. Cistii), or of branchlets with secondary whorls of similar leaves (C. SuckoviiandC. undulatus). No Calamite known to me bears broad one-nerved leaves like those ofAsterophyllitesandAnnularia, though the larger stems of these plants have been described as Calamites, and the termCalamocladushas been used to include both groups. The base of the Calamite stem usually terminates in a blunt point, and may be attached to a rhizome, or several stems may bud out from each other in a group or stool. The roots are long and cylindrical, sometimes branching. The fruit consists of spikes of spore-cases, borne in whorls and subtended by linear floral leaves. To these strobiles the name Calamostachys has been given.

Williamson has shown that the stem of Calamites consists of a central pith or cavity of large size surrounded by a cylinder consisting of alternate wedges of woody and cellular matter, with vertical canals at the inner sides of the wedges, and slender medullary rays. The thick cellular wedges intervening between the woody wedges he calls primary medullary rays; the smaller medullary rays in the wedges, secondary medullary rays. There is thus a highly complex exogenous stem based on the same principle with the stem of a commonEquisetum, but with much greater strength and complexity.

Williamson has also shown that there are different sub-types of these stems. More especially he refers to the three following:

(a)Calamitesproper, which has the woody wedges of scalariform or barred tissue with thin medullary rays, and the thick primary medullary rays are cellular.

(b)Calamopitushas reticulated or multiporous tissue in the woody wedges with medullary rays, and the primary medullary wedges are composed of elongated cells.

(c)Calamodendronhas the woody wedges of barred tissue as ina, with medullary rays, but has the intervening medullary wedges of an elongated tissue approaching to woody fibre, and also with medullary rays.

To these I would add a fourth type, which I have described, from the coal-formation of Nova Scotia.[DB]

[DB]“Quarterly Journal of the Geological Society,” 1871.

(d)Eucalamodendrondiffers fromCalamodendronin having true bordered pores or pseudo-scalariform slit-pored tissue, and corresponds to the highest type of calamitean stem.

I would also add that underaandbthere are some species in which the woody cylinder is very thin in comparison to the size of the stem. Incanddthe woody cylinder is thick and massive, and the stems are often large and nodose.

As an example of an ordinary Calamite in which the external surface and foliage are preserved, I may quote the following from my report on the “Flora of the Lower Carboniferous and Millstone Grit,” 1873:

Calamites Undulatus, Brongniart.—This species is stated by Brongniart to be distinguished from theC. Suckovii, the characteristic Calamite of the middle coal-formation, by its undulated ribs marked with peculiar cellular reticulation. He suggests that it may be merely a variety ofC. Suckovii, an opinion in which Schimper coincides; but since I have received large additional collections from Mr. Elder, containing not only the stems and branches, but also the leaves and rhizomes, I am constrained to regard it as a distinct though closely allied species.

The rhizomata are slender, being from one to two inches in diameter, and perfectly flattened. They are beautifully covered with a cellular reticulation on the thin bark, and show occasional round areoles marking the points of exit of the rootlets. I have long been familiar with irregular flattened stems thus reticulate, but have only recently been able to connect them with this species of Calamite.

The main stems present a very thin carbonaceous bark reticulated like the rhizomes. They have flat, broad ribs separated by deepand narrow furrows, and undulated in a remarkable manner even when the stems are flattened. This undulation is, however, perhaps an indication of vertical pressure while the plant was living, as it seems to have had an unusually thin and feeble cortical layer, and the undulations are apparently best developed in the lower part of the stem. At the nodes the ribs are often narrowed and gathered together, especially in the vicinity of the rounded radiating marks which appear to indicate the points of insertion of the branches. At the top of each rib we have the usual rounded areole, probably marking the insertion of a primary branchlet.

The branches have slender ribs and distant nodes, from which spring secondary branchlet s in whorls, these bearing in turn small whorls of acicular leaflets much curved upward, and which are apparently round in cross section and delicately striate. They are much shorter than the leaves ofCalamites Suckovii, and are less dense and less curved than those ofC. nodosus, which I believe to be the two most closely allied species.

Lesquereux notices this species as characteristic of the lower part of the Carboniferous in Arkansas.

It will be observed that I regard the striated and ribbed stems not as internal axes, but as representing the outer surface of the plants. This was certainly the case with the present species and withC. SuckoviiandC. nodosus. Other species, and especially those which belonged to Calamodendron, no doubt had a smooth or irregularly wrinkled external bark; but this gives no good ground for the manner in which some writers on this subject confound Calamites with Calamodendra, and both with Asterophyllites and Sphenophyllum. With this no one who has studied these plants, rooted in their native soils, and with their appendages still attached, can for a moment sympathise. One of the earliest geological studies of the writer was a bed of these erect Calamites, which he showed to Sir C. Lyell in 1844, and described in the “Proceedings of the Geological Society” in 1851, illustrating the habit of growth as actually seen well exposed in a sandstone cliff. Abundant opportunities of verifying the conclusions formed at that time have since occurred, the results of which have been summed up in the figures in Acadian Geology, which, though they have been treated by some botanists as merely restorations, are in reality representations of facts actually observed.

On these subjects, without entering into details, and referring for these to the elaborate discussions of Schimper, Williamson, and McNab, and to my paper on the subject, “Journal of the Geological Society,” vol. xxvii, p. 54, I may remark:

1. That the aërial stems of ordinary Calamites had a thin cortical layer, with lacunæ and fibrous bundles and multiporous vessels—the whole not differing much from the structure of modern Equiseta.

2. Certain arborescent forms, perhaps allied to the true Calamites, as well as possibly the old underground stems of ordinary species[DC]assumed a thick-walled character in which the tissues resembled the wedges of an exogen, and abundance of pseudo-scalariform fibres were developed, while the ribbing of the external surface became obsolete or was replaced by a mere irregular wrinkling.

[DC]Williamson, “Transactions of the Royal Society.” McNab, in “Proceedings of the Edinburgh Botanical Society.”

3. Sufficient discrimination has not been exercised in separating casts of the internal cavities of Calamites and Calamodendron from those representing other surfaces and the proper external surface.

4. There is no excuse for attributing to Calamites the foliage of Annularia, Asterophyllites, and Sphenophyllum, since these leaves have not been found attached to true Calamite stems, and since the structure of the stems of Asterophyllites as described by Williamson, and that of Sphenophyllum as described by the writer,[DD]are essentially different from those of Calamites.

[DD]“Journal of the Geological Society,” 1866.

5. As the species above described indicates, good external characters can be found for establishing species of this genus, and these species are of value as marks of geological age.

GenusArchæocalamites, Sternberg.

This genus has been established to include certain Calamites of the Devonian and Lower Carboniferous, in which the furrows on the stem do not alternate at the nodes or joints, and the leaves in one species at least bifurcate.C. radiatus, Brongniart, is the typical species. In North America it occurs in the Erian, probably as low as the Middle Erian. In Europe it has so far been recognised in the Lower Carboniferous only. I have, however, seen stems from alleged Devonian beds in Devonshire which may have belonged to this species.

FamilyAsterophylliteæ;GenusAsterophyllites, Brongniart.

Stems ribbed and jointed like theCalamites, but with inflated nodes and a stout internal woody cylinder, which has been described by Williamson. From the joints proceeded whorls of leaves or of branchlets, bearing leaves which differed from those ofCalamitesin their having a distinct middle rib or vein. The fructification consistedof long slender cones or spikes, having whorls of scales bearing the spore-cases. Some authors speak ofAsterophyllitesas only branches and leaves ofCalamites; but though at first sight the resemblance is great, a close inspection shows that the leaves of Asterophyllites have a true midrib, which is wanting inCalamites.

GenusAnnularia.—It is perhaps questionable whether these plants should be separated fromAsterophyllites, The distinction is that they produce branches in pairs, and that their whorls of leaves are one-sided and usually broader than those ofAsterophyllites, and united into a ring at their insertion on the stem. One little species,A. sphenophylloides, is very widely distributed.

Pinnularia—a provisional genus—-includes slender roots or stems branching in a pinnate manner, and somewhat irregularly. They are very abundant in the coal shales, and were probably not independent plants, but aquatic roots belonging to some of the plants last mentioned. The probability of this is farther increased by their resemblance in miniature to the roots ofCalamites. They are always flattened, but seem originally to have been round, with a slender thread-like axis of scalariform vessels, enclosed in a soft, smooth, cellular bark.

FamilyRhizocarpeæ;GenusSphenophyllum.

Leaves in whorls, wedge-shaped, with forking veins. Fructification on spikes, with verticils of sporocarps. These plants are by some regarded as allied to theCalamiteæandAsterophylliteæ, by others as a high grade of Rhizocarps of the type of Marsilia. The stem had a star-shaped central bundle of scalariform or reticulato-scalariform vessels.

GenusSporangites. (Sporocarpon, Williamson.)

Under this name we may provisionally include those rounded spherical bodies found in the coal and its accompanying beds, and also in the Erian, which may be regarded as Macrospores or Sporocarps of Protosalvinia, or other Rhizocarpean plants akin to those described above inChapter III, which see for description.

GenusProtosalvinia.—Under this we include sporocarps allied to those ofSalvinia, as described inChapter III.

FamilyFilices.

Under this head I shall merely refer to a few groups of special interest, and to the provisional arrangement adopted for the fronds of ferns when destitute of fructification.

The external appearances of trunks of tree-ferns have been already referred to.

With respect to tree ferns, the oldest known examples are those from the Middle Devonian of New York and Ohio, which I have described in the “Journal of the Geological Society,” 1871 and 1881. As these are of some interest, I have reproduced their descriptions in anoteappended to Chapter III, which see.

The other forms most frequently occurring in the Carboniferous areCaulopteris,Palæopteris, andMegaphyton[DE]Stems showing merely masses of aërial roots are known by the namePsaronius.

[DE]See my “Acadian Geology,” also below.

With reference to the classification of Palæozoic ferns, this has hitherto been quite arbitrary, being based on mere form and venation of fronds, but much advance has recently been made in the knowledge of their fructification, warranting a more definite attempt at classification. The following are provisional genera usually adopted:

1.Cyclopteris, Brongniart.—Leaflets more or less rounded or wedge-shaped, without midrib, the nerves spreading from the point of attachment. This group includes a great variety of fronds evidently of different genera, were their fructification known; and some of them probably portions of fronds, the other parts of which may be in the next genus.

2.Neuropteris, Brongniart.—Fronds pinnate, and with the leaflets narrowed at the base; midrib often not distinct, and disappearing toward the apex. Nervures equal, and rising at an acute angle. Ferns of this type are among the most abundant in the coal-formation.

3.Odontopteris, Brongniart.—In these the frond is pinnate, and the leaflets are attached by their whole base, with the nerves either proceeding wholly from the base, or in part from an indistinct midrib, which soon divides into nervures.

4.Dictyopteris, Gutbier.—This is a beautiful style of fern, with leaflets resembling those ofNeuropteris, but the veins arranged in a network of oval spaces. Only a few species are known in the coal-formation.

5.Lonchopteris, Brongniart.—Ferns with netted veins like the above, but with a distinct midrib, and the leaflets attached by the whole base. Of this, also, we can boast but few species.

6.Sphenopteris, Brongniart.—These are elegant ferns, very numerous in species, and most difficult to discriminate. Their mostdistinctive characters are leaflets narrowed at the base, often lobed, and with nervures dividing in a pinnate manner from the base.

7.Phyllopteris, Brongniart.—These are pinnate, with long lanceolate pinnules, having a strong and well-defined midrib, and nerves proceeding from it very obliquely, and dividing as they proceed toward the margin. The ferns of this genus are for the most part found in formations more recent than the Carboniferous; but I have referred to it, with some doubt, one of our species.

8.Alethopteris, Brongniart.—This genus includes many of the most common coal-formation ferns, especially the ubiquitousA. lonchitica, which seems to have been the common brake of the coal-formation, corresponding toPteris aquilinain modern Europe and America. These are brake-like ferns, pinnate, with leaflets often long and narrow, decurrent on the petiole, adherent by their whole base, and united at base to each other. The midrib is continuous to the point, and the nervures run off from it nearly at right angles. In some of these ferns the fructification is known to have been marginal, as inPteris.

9.Pecopteris, Brongniart.—This genus is intermediate between the last andNeuropteris. The leaflets are attached by the whole base, but not usually attached to each other; the midrib, though slender, attains to the summit; the nervures are given off less obliquely than inNeuropteris. This genus includes a large number of our most common fossil ferns.

10.Beinertia, Goeppert.—A genus established by Goeppert for a curious Pecopteris-like fern, with flexuous branching oblique nervures becoming parallel to the edge of the frond.

11.Hymenophyllites, Goeppert.—These are ferns similar to Sphenopteris, but divided at the margin into one-nerved lobes, in the manner of the modern genusHymenophyllum.

12.Palæopteris, Geinitz.—This is a genus formed to include certain trunks of tree-ferns with oval transverse scars of leaves.

13.Caulopteris, Lindley and Hutton.—Is another genus of fossil trunks of tree-ferns, but with elongate scars of leaves.

14.Psaronius, Cotta.—Includes other trunks of tree-ferns with alternate scars or thick scales, and ordinarily with many aërial roots grouped round them, as in some modern tree-ferns.

15.Megaphyton, Artis.—Includes trunks of tree-ferns which bore their fronds, which were of great size, in two rows, one on each side of the stem. These were very peculiar trees, less like modern ferns than any of the others. My reasons for regarding them as ferns are stated in the following extract from a recent paper:

“Their thick stems, marked with linear scars and having two rows of large depressed areoles on the sides, suggest no affinities to any known plants. They are usually ranked withLepidodendronandUlodendron, but sometimes, and probably with greater reason, are regarded as allied to tree-ferns. At the Joggins a very fine species (M. magnificum) has been found, and at Sydney a smaller species (M. humile); but both are rare and not well preserved. If the large scars bore cones and the smaller bore leaves, then, as Brongniart remarks, the plant would much resembleLepidophloios, in which the cone-scars are thus sometimes distichous. But the scars are not round and marked with radiating scales as inLepidophloios; they are reniform or oval, and resemble those of tree-ferns, for which reason they may be regarded as more probably leaf-scars; and in that case the smaller linear scars would indicate ramenta, or small aërial roots. Further, the plant described by Corda asZippea distichais evidently aMegaphyton, and the structure of that species is plainly that of a tree-fern of somewhat peculiar type. On these grounds I incline to the opinion of Geinitz that these curious trees were allied to ferns, and bore two rows of large fronds, the trunks being covered with coarse hairs or small aërial roots. At one time I was disposed to suspect that they may have crept along the ground; but a specimen from Sydney shows the leaf-stalks proceeding from the stem at an angle so acute that the stem must, I think, have been erect. From the appearance of the scars it is probable that only a pair of fronds were borne at one time at the top of the stem; and, if these were broad and spreading, it would be a very graceful plant. To what extent plants of this type contributed to the accumulation of coal I have no means of ascertaining, their tissues in the state of coal not being distinguishable from those of ferns andLycopodiaceæ.”

16. For descriptions of the genusArchæopterisand other Erian ferns, seeChapter III.

CHAPTER V.

THE FLORA OF THE EARLY MESOZOIC.

Greatphysical changes occurred at the close of the Carboniferous age. The thick beds of sediment that had been accumulating in long lines along the primitive continents had weighed down the earth’s crust. Slow subsidence had been proceeding from this cause in the coal-formation period, and at its close vast wrinklings occurred, only surpassed by those of the old Laurentian time. Hence in the Appalachian region of America we have the Carboniferous beds thrown into abrupt folds, their shales converted into hard slates, their sandstones into quartzite and their coals into anthracite, and all this before the deposition of the Triassic Red Sandstones which constitute the earliest deposit of the great succeeding Mesozoic period. In like manner the coal-fields of Wales and elsewhere in western Europe have suffered similar treatment, and apparently at the same time.

This folding is, however, on both sides of the Atlantic limited to a band on the margin of the continents, and to certain interior lines of pressure, while in the middle, as in Ohio and Illinois in America, and in the great interior plains of Europe, the coal-beds are undisturbed and unaltered. In connection with this we have an entire change in the physical character of the deposits, a great elevation of the borders of the continents, and probably a considerable deepening of the seas, leading to the establishment of general geographical conditions which still remain, though they have been temporarily modified by subsequent subsidences and re-elevations.

Along with this a great change was in progress in vegetable and animal life. The flora and fauna of the Palæozoic gradually die out in the Permian and are replaced in the succeeding Trias by those of the Mesozoic time. Throughout the Permian, however, the remains of the coal-formation flora continue to exist, and some forms, as theCalamites, even seem to gain in importance, as do also certain types of coniferous trees. The Triassic, as well as the Permian, was marked by physical disturbances, more especially by great volcanic eruptions discharging vast beds and dykes of lava and layers of volcanic ash and agglomerate. This was the case more especially along the margins of the Atlantic, and probably also on those of the Pacific. The volcanic sheets and dykes associated with the Red Sandstones of Nova Scotia, Connecticut, and New Jersey are evidences of this.

At the close of the Permian and beginning of the Trias, in the midst of this transition time of physical disturbance, appear the great reptilian forms characteristic of the age of reptiles, and the earliest precursors of the mammals, and at this time the old Carboniferous forms of plants finally pass away, to be replaced by a flora scarcely more advanced, though different, and consisting of pines, cycads, and ferns, with gigantic equiseta, which are the successors of the genusCalamites, a genus which still survives in the early Trias. Of these groups the conifers, the ferns, and the equiseta are already familiar to us, and, in so far as they are concerned, a botanist who had studied the flora of the Carboniferous would have found himself at home in the succeeding period. The cycads are a new introduction. The whole, however, come within the limits of the cryptogams and the gymnosperms, so that here we have no advance.[DF]

[DF]Fontaine’s “Early Mesozoic Flora of Virginia” gives a very good summary of this flora in America.

Fig. 64.—Jurassic vegetation. Cycads and pines. (After Saporta.)

As we ascend, however, in the Mesozoic, we find new and higher types. Even within the Jurassic epoch, the next in succession to the Trias, there are clear indications of the presence of the endogens, in species allied to the screw-pines and grasses; and the palms appear a little later, while a few exogenous trees have left their remains in the Lower Cretaceous, and in the Middle and Upper Cretaceous these higher plants come in abundantly and in generic forms still extant, so that the dawn of the modern flora belongs to the Middle and UpperCretaceous. It will thus be convenient to confine ourselves in this chapter to the flora of the earlier Mesozoic.

Passing over for the present the cryptogamous plants already familiar in older deposits, we may notice the new features of gymnospermous and phænogamous life, as they present themselves in this earlier part of the great reptilian age, and as they extended themselves with remarkable uniformity in this period over all parts of the world. For it is a remarkable fact that, if we place together in our collections fossil plants of this period from Australia, India, China, Siberia, Europe, or even from Greenland, we find wonderfully little difference in their aspect. This uniformity we have already seen prevailed in the Palæozoic flora; and it is perhaps equally marked in that of the Mesozoic. Still we must bear in mind that some of the plants of these periods, as the ferns and pines, for example, are still world-wide in their distribution; but this does not apply to others, more especially the cycads (Fig. 65).

Fig. 65.—Podozamites lanceolatus, Sternb. L. Cretaceous.

The cycads constitute a singular and exceptional type in the modern world, and are limited at present to the warmer climates, though very generally distributed in these, as they occur in Africa, India, Japan, Australia, Mexico, Florida, and the West Indies. In the Mesozoic age, however, they were world-wide in their distribution, and are found as far north as Greenland, though most of the species found in the Cretaceousof that country are of small size/ and may have been of low growth, so that they may have been protected by the snows of winter. The cycads have usually simple or unbranching stems, pinnate leaves borne in a crown at top, and fruits which, though somewhat various in structure and arrangement, are all of the simpler form of gymnospermous type. The stems are exogenous in structure, but with slender wood and thick bark, and barred tissue, or properly as tissue intermediate between this and the disc-bearing fibres of the pines.

Though the cycads have a considerable range of organisation and of fructification, and though some points in reference to the latter might assign them a higher place, on the whole they seem to occupy a lower position than the conifers or the cordaiteæ of the Carboniferous. In the Carboniferous some of the fern-like leaves assigned to the genusNoeggerathiahave been shown by Stur and Weiss to have been gymnosperms, probably allied to cycads, of which they may be regarded at least as precursors. Thus the cycadean type does not really constitute an advance in grade of organisation in the Mesozoic, any further than that, in the period now in question, it becomes much more developed in number and variety of forms. But the conifers would seem to have had precedence of it for a long time in the Palæozoic, and it replaces in the Mesozoic theCordaites, which in many respects excelled it in complexity.

The greater part of the cycads of the Mesozoic age would seem to have had short stems and to have constituted the undergrowth of woods in which conifers attained to greater height. An interesting case of this is the celebrated dirt-bed of the quarries of the Isle of Portland, long ago described by Dean Buckland. In this fossil soil trunks of pines, which must have attained to great height, are interspersed with the short, thick stems of cycads, of the genus namedCycadoideaby Buckland,and which from their appearance are called “fossil birds' nests” by the quarrymen. Some, however, must have attained a considerable height so as to resemble palms.

The cycads, with their simple, thick trunks, usually marked with rhombic scars, and bearing broad spreading crowns of large, elegantly formed pinnate leaves, must have formed a prominent part of the vegetation of the northern hemisphere during the whole of the Mesozoic period. A botanist, had there been such a person at the time, would have found this to be the case everywhere from the equator to Spitzbergen, and probably in the southern hemisphere as well, and this throughout all the long periods from the Early Trias to the Middle Cretaceous. In a paper published in the “Linnæan Transactions” for 1868, Dr. Carruthers enumerates twenty species of British Mesozoic cycads, and the number might now be considerably increased.

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