The Testimony of the Rocks Part 3

LYCOPODIUM CLAVATUM.]

[Ill.u.s.tration: Fig. 8.

EQUISETUM FLUVIATILE.]

We stand, at low ebb, on the outer edge of one of those iron-bound sh.o.r.es of the Western Highlands, rich in forests of algae, from which, not yet a generation bygone, our Celtic proprietors used to derive a larger portion of their revenues than from their fields and moors. Rock and skerry are brown with sea weed. The long cylindrical lines of _Chorda filum_, many feet in length, lie aslant in the tideway; long s.h.a.ggy bunches of _Fucus serratus_ and _Fucus nodosus_ droop heavily from the rock sides; while the flatter ledges, that form the uneven floor upon which we tread, bristle thick with the stiff, cartilaginous, many-cleft fronds of at least two species of chondrus,--the common carrageen, and the smaller species, _C. Norvegicus_. Now, in the thickly-spread fucoids of this Highland sh.o.r.e we have not a _very_ inadequate representation of the first, or thallogenic vegetation,--that of the great Silurian period, as exhibited in the rocks, from the base to nearly the top of the system. And should we add to the rocky tract, rich in fucoids, a submarine meadow of pale sh.e.l.l sand, covered by a deep green swathe of zostera, with its jointed saccharine roots and slim flowers, unfurnished with petals, we would render it perhaps more adequately representative still.

[Ill.u.s.tration: Fig. 9.

OSMUNDA REGALIS. (Royal Fern.)]

We cross the beach, and enter on a bare brown moor, comparatively fertile, however, in the club mosses. One of the largest and finest of the species, _Lycopodium clavatum_, with its long scaly stems and upright spikes of lighter green,--altogether a graceful though flowerless plant, which the herd-boy learns to select from among its fellows, and to bind round his cap,--goes trailing on the drier spots for many feet over the soil; while at the edge of trickling runnel or marshy hollow, a smaller and less hardy species, _Lycopodium inundatum_, takes its place. The marshes themselves bristle thick with the deep green horse tail, _Equisetum fluviatile_, with its fluted stem and verticillate series of linear brandies. Two other species of the same genus, _Equisetum sylvatic.u.m_ and _Equisetum arvense_, flourish on the drier parts of the moor, blent with two species of minute ferns, the moonwort and the adder's tongue,--ferns that, like the magnificent royal fern (_Osmunda regalis_), though on a much humbler scale, bear their seed cases on independent stems, and were much sought after of old for imaginary virtues, which the modern schools of medicine refuse to recognize. Higher up the moor, ferns of ampler size occur, and what seems to be rushes, which bear atop conglobate panicles on their smooth leafless stems; but at its lower edge little else appears than the higher Acrogens,--ferns and their allies. There occurs, however, just beyond the first group of club mosses,--a remarkable exception in a solitary pine,--the advance guard of one of the ancient forests of the country, which may be seen far in the background, clothing with its s.h.a.ggy covering of deep green the lower hill-slopes. And as we found in the Thallogens of that littoral zone over which we have just pa.s.sed, representatives of the marine flora of the Silurian System, from the first appearance of organisms in its nether beds, to its bone-bed of the Upper Ludlow rocks, in which the Lycopodites first appear, so in the Acrogens of that moor, with its solitary coniferous tree, we may recognize an equally striking representative of the terrestrial flora which existed during the deposition of these Ludlow rocks, and of the various formations of the Old Red Sandstone, Lower, Middle, and Upper.

[Ill.u.s.tration: Fig. 10.

PINUS SYLVESTRIS. (Scotch Fir.)]

[Ill.u.s.tration: Fig. 11.

CALAMITE? Of the Lower Old Red Sandstone. Shetland. (One eighth nat.

size.)]

[Ill.u.s.tration: Fig. 12.

LYCOPODITE? Of the Lower Old Red Sandstone. Thurso. (Mag. two diameters.)]

In the upper beds of the Upper Silurian, as has been already remarked, Lycopodites are the only terrestrial plants yet found. In the Lower Old Red Sandstone we find added to these, with Thallogens that bear at least the same _general_ character as in the system beneath, minute ferns, and a greatly larger plant, allied to the horse tails. The Old Red flora seems to have been prevailingly an acrogenic flora; and yet with almost its first beginnings,--contemporary with at least the earlier fossils of the system in Scotland, we find a true polycotyledonous tree, not lower in the scale than the araucarites of the Coal Measures,--which in structure it greatly resembles,--or than the pines or cedars of our own times (see Fig. 3). In the Middle Old Red Sandstone there occurs, with plants representative apparently of the ferns and their allies, a somewhat equivocal and doubtful organism, which may have been the panicle or compound fruit of some aquatic rush; while in the Upper Old Red, just ere the gorgeous flora of the Coal Measures began to be, there existed in considerable abundance a stately fern, the _Cyclopteris Hibernicus_ (see Fig. 2), of mayhap not smaller proportions than our monarch of the British ferns, _Osmunda regalis_, a.s.sociated with a peculiar lepidodendron, and what seems to be a lepidostrobus,--possibly the fructiferous spike or cone of the latter, mingled with carbonaceous stems, which, in the simplicity of their texture, and their abundance, give evidence of a low but not scanty vegetation. Ere pa.s.sing to the luxuriant carboniferous flora, I shall make but one other remark. The existing plants whence we derive our a.n.a.logies in dealing with the vegetation of this early period, contribute but little, if at all, to the support of animal life. The ferns and their allies remain untouched by the grazing animals. Our native club mosses, though once used in medicine, are positively deleterious; the horse tails, though harmless, so abound in silex, which wraps them round with a cuticle of stone, that they are rarely cropped by cattle; while the thickets of fern which cover our hill-sides, and seem so temptingly rich and green in their season, scarce support the existence of a single creature, and remain untouched in stem and leaf, from their first appearance in spring, until they droop and wither under the frosts of early winter. Even the insects that infest the herbaria of the botanist almost never injure his ferns.

Nor are our resin-producing conifers, though they nourish a few beetles, favorites with the herbivorous tribes in a much greater degree. Judging from all we yet know, the earliest terrestrial flora may have covered the dry land with its mantle of cheerful green, and served its general purposes, chemical and others, in the well-balanced economy of nature; but the herb-eating animals would have fared but ill even where it throve most luxuriantly; and it seems to harmonize with the fact of its non-edible character, that up to the present time we know not that a single herbivorous animal lived among its shades. From all that appears, it may be inferred that it had not to serve the purposes of the floras of the pa.s.sing time, in which, according to the poet,

"The world's bread depends on the shooting of a seed."

[Ill.u.s.tration: Fig. 13.

FERN? of Lower Old Red Sandstone. Orkney.

(Nat. Size.)]

The flora of the Coal Measures was the richest and most luxuriant, in at least individual productions, with which the fossil botanist has formed any acquaintance. Never before or since did our planet bear so rank a vegetation as that of which the numerous coal seams and inflammable shales of the carboniferous period form but a portion of the remains,--the portion spared, in the first instance, by dissipation and decay, and in the second by the denuding agencies. Almost all our coal,--the stored up fuel of a world,--forms but a comparatively small part of the produce of this wonderful flora. Amid much that was so strange and antique of type in its productions as to set the a.n.a.logies of the botanist at fault, there occurred one solitary order, not a few of whose species closely resembled their cogeners of the present time. I refer, of course, to its ferns. And these seem to have formed no small proportion of the entire flora of the period. Francis estimates the recent dorsiferous ferns of Great Britain at thirty-five species, and the species of all the other genera at six more,--forty-one species in all; and as the flowering plants of the country do not fall short of fourteen hundred species, the ferns bear to them the rather small proportion of about one to thirty-five; whereas of the British Coal Measure flora, in which we do not yet reckon quite three hundred species of plants, about a hundred and twenty were ferns. Three sevenths of the entire carboniferous flora of Britain belonged to this familiar cla.s.s; and for about fifty species more we can discover no nearer a.n.a.logies than those which connect them with the fern allies. And if with the British Coal Measure we include those also of the Continent of America, we shall find the proportions in favor of the ferns still greater. The number of carboniferous plants. .h.i.therto described amounts, says M. Ad.

Brogniart, to about five hundred, and of these two hundred and fifty,--one half of the whole,--were ferns.

[Ill.u.s.tration: Fig. 14.]

[Ill.u.s.tration: Fig. 15.]

[Ill.u.s.tration: Fig. 16.]

[Ill.u.s.tration: Fig. 17.]

[Ill.u.s.tration: Fig. 18.]

[Ill.u.s.tration: Fig. 19.]

[Ill.u.s.tration: FERNS OF THE COAL MEASURES.[6]]

[Ill.u.s.tration: Fig. 20.

ALTINGIA EXCELSA.

Norfolk Island Pine. (Young Specimen.)]

Rising in the scale from the lower to the higher vegetable forms of the system,--from its ferns to its trees,--we find great conifers,--so great that they must have raised their heads more than a hundred feet over the soil; and such was their abundance in this neighborhood, that one can scarce examine a fragment of coal beside one's household fire that is not charged with their carbonized remains. Though marked by certain peculiarities of structure, they bore, as is shown by the fossil trunks of Granton and Craigleith, the familiar outlines of true coniferous trees; and would mayhap have differed no more in appearance from their successors of the same order that now live in our forests, than these differ from the conifers of New Zealand or of New South Wales. We have thus, in the numerous ferns and numerous coniferous trees of the Coal Measures, known objects by which to conceive of some of the more prominent features of the flora of which they composed so large a part.

We have not inadequate conceptions of at once the giants of its forests and the green swathe of its plains and hill-sides,--of its mighty trees and its dwarf _underwood_,--of its cedars of Lebanon, so to speak, and its hyssop of the wall. But of an intermediate cla.s.s we have no existing representatives; and in this cla.s.s the fossil botanist finds puzzles and enigmas with which hitherto at least he has been able to deal with only indifferent success. There is a view, however, sufficiently simple, which may be found somewhat to lessen, if not altogether remove, the difficulty. Nature does not dwell willingly in mediocrity; and so in all ages she as certainly produced trees, or plants of tree-like proportions and bulk, as she did minute shrubs and herbs. In not a few of the existing orders and families, such as the Rosaceae, the Leguminosae, the Myrtaceae, and many others, we have plants of all sizes, from the creeping herb, half hidden in the sward, to the stately tree. The wild dwarf strawberry and minute stone-bramble are of the same order as our finer orchard trees,--apple, pear, and plum,--or as those n.o.ble hawthorn, mountain ash, and wild cherry trees, that impart such beauty to our lawns and woods; and the minute spring vetch and everlasting pea are denizens of the same great family as the tall locust and rosewood trees, and the gorgeous laburnum. Did there exist no other plants than the Rosaceae or the Leguminosae, we would possess, notwithstanding, herbs, shrubs, and trees, just as we do now. And in plants of a greatly humbler order we have instances of similar variety in point of size. The humblest gra.s.s in our meadows belongs to the same natural order as the tall bamboo, that, shooting up its panicles amid the jungles of India to the height of sixty feet, looks down upon all the second cla.s.s trees of the country. Again, the minute forked spleenwort of Arthur Seat, which rarely exceeds three inches in length, is of the same family as those tree-ferns of New Zealand and Tasmania that rise to an elevation of from twenty to thirty feet. And we know how in the ferns provision is made for the attainment and maintenance of the tree-like size and character. The rachis, which in the smaller species is either subterranean or runs along the ground, takes in the tree-fern a different direction, and, rising erect, climbs slowly upwards in the character of a trunk or stem, and sends out atop, year after year, a higher and yet higher coronal of fronds. And in order to impart the necessary strength to this trunk, and to enable it to war for ages with the elements, its ma.s.s of soft cellular tissue is strengthened all round by internal b.u.t.tresses of dense vascular fibre, tough and elastic as the strongest woods. Now, not a few of the more anomalous forms of the Coal Measures seem to be simply fern allies of the types Lycopodiaceae, Marsileaceae, and Equisetum, that, escaping from the mediocrity of mere herbs, shot up into trees,--some of them very great trees,--and that had of necessity to be furnished with a tissue widely different from that of their minuter contemporaries and successors. It was of course an absolute mechanical necessity, that if they were to present, by being tall and large, a wide front to the tempest, they should also be comparatively solid and strong to resist it; but with this simple mechanical requirement there seems to have mingled a principle of a more occult character. The Gymnogens or conifers were the highest vegetable existences of the period,--its true trees; and all the tree-like fern allies were strengthened to meet the necessities of their increased size, on, if I may so speak, a _coniferous_ principle. Tissue resembling that of their contemporary conifers imparted the necessary rigidity to their framework; nay, so strangely were they pervaded throughout by the coniferous characteristics, that it seems difficult to determine whether they really most resembled the acrogenous or gymnogenous families. The Lepidodendra,--great plants of the club moss type, that rose from fifty to seventy feet in height,--had well nigh as many points of resemblance to the coniferae as to the Lycopodites. The Calamites,--reed-like, jointed plants, that more nearly resemble the Equisetaceae than aught else which now exists, but which attained, in the larger specimens, to the height of ordinary trees, also manifest very decidedly, in their internal structure, some of the characteristics of the conifers. It has been remarked by Lindley and Hutton of even Sphenophyllum,--a genus of plants with verticillate leaves, of which at least six species occur in our Coal Measures, and which Brogniart refers to one of the humblest families of the fern allies,--that it seems at least as nearly related to the Coniferae as to its lowlier representatives, the Marsileaceae. And it is this union of traits, pertaining to what are now widely separated orders, that imparts to not a few of the vegetables of the Coal Measures their singularly anomalous character.

[Ill.u.s.tration: Fig. 21.

EAST INDIA TREE-FERN.[7]

(_Asophila perrotetiana._)]

[Ill.u.s.tration: Fig. 22.

SECTION OF STEM OF TREE-FERN.[8]

(_Cyathea._)]

[Ill.u.s.tration: Fig. 23.]

[Ill.u.s.tration: Fig. 24.]

[Ill.u.s.tration: Fig. 25.]

[Ill.u.s.tration: LEPIDODENDRON STERNBERGII.[9]]

[Ill.u.s.tration: Fig. 26.

CALAMITES MOUGEOTII.]

[Ill.u.s.tration: Fig. 27.

SPHENOPHYLLUM DENTATUM.]

[Ill.u.s.tration: Fig. 28.

SIGILLARIA RENIFORMIS.]

Let me attempt introducing you more intimately to one of those plants which present scarce any a.n.a.logy with existing forms, and which must have imparted so strange a character and appearance to the flora of the Coal Measures. The Sigillaria formed a numerous genus of the Carboniferous period: no fewer than twenty-two different species have been enumerated in the British coal fields alone; and such was their individual abundance, that there are great seams of coal which seem to be almost entirely composed of their remains. At least the ancient soil on which these seams rest, and on which their materials appear to have been elaborated from the elements, is in many instances as thickly traversed by their underground stems as the soil occupied by our densest forests is traversed by the tangled roots of the trees by which it is covered; and we often find a.s.sociated with them in these cases the remains of no other plant. The Sigillaria were remarkable for their beautifully sculptured stems, various in their pattern, according to their species. All were fluted vertically, somewhat like columns of the Grecian Doric; and each flute or channel had its line of sculpture running adown its centre. In one species (_S. flexuosa_) the sculpture consists of round k.n.o.bs, surrounded by single rings, like the heads of the bolts of the s.h.i.+p carpenter; in another (_S. reniformis_) the k.n.o.bs are double, and of an oval form, somewhat resembling pairs of kidneys,--a resemblance to which the species owes its name. In another species (_S. catenulata_) what seems a minute chain of distinctly formed elliptical links drops down the middle of each flute; in yet another (_S. oculata_) the carvings are of an oval form, and, bearing each a round impression in its centre, they somewhat resemble rows of staring goggle-eyes; while the carvings in yet another species (_S.

pachyderma_) consist chiefly of crescent-shaped depressions. The roots, or rather underground stems, of this curious genus attracted notice, from their singularity, long ere their connection with the carved and fluted stems had been determined, and have been often described as the "stigmaria" of the fossil botanist. They, too, have their curious carvings, consisting of deeply marked stigmata, quincuncially arranged, with each a little ring at its bottom, and, in at least one rare species, surrounded by a sculptured star. Unlike true roots, they terminate abruptly; each rootlet which they send forth was jointed to the little ring or dimpled k.n.o.b at the bottom of the stigmata; and the appearance of the whole, as it radiated from the central ma.s.s, whence the carved trunk proceeded, somewhat resembled that of an enormous coach-wheel divested of the rim. Unfortunately we cannot yet complete our description of this strange plant. A specimen, traced for about forty feet across a shale bed, was found to bifurcate atop into two great branches,--a characteristic in which, with several others, it differed from most of the tree-ferns,--a cla.s.s of plants to which Adolphe Brogniart is inclined to deem it related; but no specimen has yet shown the nature of its foliage. I am, however, not a little disposed to believe with Brogniart that it may have borne as leaves some of the supposed ferns of the Coal Measures; nowhere, at least, have I found these lie so thickly, layer above layer, as around the stems of Sigillaria; and the fact that, even in our own times, plants widely differing from the tree-ferns,--such, for instance, as one of the Cycadeae,--should bear leaves scarce distinguishable from fern fronds, may well reconcile us to an apparent anomaly in the case of an ancient plant such as Sigillaria, whose entire const.i.tution, so far as it has been ascertained, appears to have been anomalous. The sculpturesque character of this richly fretted genus was shared by not a few of its contemporaries. The Ulodendra, with their rectilinear rows of circular scars, and their stems covered with leaf-like carvings, rivalled in effect the ornately relieved torus of a Corinthian column: Favularia, Knorria, Halonia, many of the Calamites, and all the Lepidodendra, exhibited the most delicate sculpturing. In walking among the ruins of this ancient flora, the Palaeontologist almost feels as if he had got among the broken fragments of Italian palaces, erected long ages ago, when the architecture of Rome was most ornate, and every moulding was roughened with ornament; and in attempting to call up in fancy the old Carboniferous forests, he has to dwell on this peculiar feature as one of the most prominent, and to see, in the mult.i.tude of trunks darkened above by clouds of foliage, that rise upon him in the prospect, the slim columns of an elder Alhambra, roughened with arabesque tracery and exquisite filagree work.

[Ill.u.s.tration: Fig. 29.