FUCOID.
FUCOIDS.
Associated with the earliest ichthyic remains of the Old Red Sandstone, we find vegetable organisms in such abundance, that they communicate often a fissile character to the stone in which they occur. But, existing as mere carbonaceous markings, their state of keeping is usually so bad, that they tell us little else than that the antiquely-formed fishes of this remote period swam over sea bottoms darkened by forests of algæ. The prevailing plant was one furnished with a long, smooth stem, which, though it threw off, in the alternate order, numerous branches at least half as stout as itself, preserved its thickness for considerable distances without diminution,—a common fucoidal characteristic. We find its remains mixed in the rock, though sparingly, with those of a rough-edged plant, knobbed somewhat like the thong-like receptacles of Himanthalia lorea, which also threw off branches like the other, but diminished more rapidly. A greatly more minute vegetable organism of the same beds, characterized by its bifid partings, which strike off at angles of about sixty, somewhat resembles the small-fronded variety of Dictyota dichotoma, save that the slim terminations of the frond are usually bent into little hooks, like the tendrils of the pea just as their points begin to turn. Another rather rare plant of the period, existing as a broad, irregularly cleft frond, somewhat resembling that of a modern Cutleria or Nitophyllum, betrays at once, in its outline and general appearance, its marine origin; as does also an equally rare contemporary, which, judging from its appearance, seems to have been a true fucus. It exists in the rock as if simply drawn in Indian ink; for it exhibits no structure, though, as in some of the ferns of the Coal Measures, what were once the curls of its leaflets continue to exist as sensible hollows on the surface. It broadens and divides atop into three or four lobes, and these, in turn, broaden and divide into minor lobes, double or ternate, and usually rounded at their terminations. In general appearance the plant not a little resembles those specimens of Fucus vesiculosus which we find existing in a diminutive form, and divested of both the receptacles and the air vessels, at the mouth of rivers. Of two other kinds of plants I have seen only confused masses, in which the individuals were so crowded together, and withal so fragmentary and broken, that their separate forms could not be traced. In the one the general appearance was such as might be produced by compressed and tangled masses of Chorda filium, in which the linear and even tubular character of the plant could be determined, but not its continuous, cord-like aspect; in the other, the fragments seemed well nigh as slim as hairs, and the appearance was such as might be produced by branches of that common ectocarpus, E. littoralis, which may be seen on our rocky coasts roughening at low water the stems of laminaria. When highly magnified, a mesial groove might be detected running along each of the hair-like lines. With these marine plants we occasionally find large rectilinear stems, resolved into a true coal, but retaining no organic character by which to distinguish them. As I have seen some of these more than three inches in diameter, and, though existing as mere fragments, several feet in length, they must, if they were also plants of the sea, have exceeded in size our largest laminaria.[46] And such are the few vegetable organisms, of apparently aquatic origin, which I have hitherto succeeded in detecting in the Lower Old Red Sandstone of Scotland.[47] Their individual numbers, however, must have been very great, though, from the destructible character of their tissues, their forms have perished in the stone. The immensely developed flagstones of Caithness seem to owe their dark color to organic matter mainly of vegetable origin. So strongly bituminous, indeed, are some of the beds of dingier tint, that they flame in the fire like slates steeped in oil.
The remains of a terrestrial vegetation in this deposit are greatly scantier than those of its marine plants; but they must be regarded as possessing a peculiar interest, as, with the exception of the spore cases of the Ludlow rocks, the oldest of their class, in at least the British islands, whose true place in the scale can be satisfactorily established. In the flagstones of Orkney there occurs, though very rarely, a minute vegetable organism, which I have elsewhere described as having much the appearance of one of our smaller ferns, such as the maidenhair-spleenwort, or dwarf moonwort. It consists of a minute stem, partially covered by what seems to be a small sheath or hollow bract, and bifurcates into two fronds or pinnæ, fringed by from ten to twelve leaflets, that nearly impinge on each other, and somewhat resemble in their mode of arrangement the leaflets of one of our commonest Aspleniums,—Asplenium trichomanes. One of our highest authorities, however, in such matters (Professor Balfour of Edinburgh) questions whether this organism be in reality a fern, and describes it from the specimen on the table, in the Palæontological chapter of his admirable Class Book, simply as "a remarkable pinnate frond." ([Fig. 13], p. 56.) We find it associated with the remains of a terrestrial plant allied to lepidodendron, and which in size and general appearance not a little resembles one of our commonest club mosses,—Lycopodium clavatum.[48] It sends out its branches in exactly the same style,—some short and simple, others branched like the parent stem,—in an arrangement approximately alternate; and is everywhere covered, stem and branch, by thickly set scale-like leaflets, that, suddenly narrowing, terminate in exceedingly slim points. It has, however, proportionally a stouter stem than Lycopodium; its leaves, when seen in profile, seem more rectilinear and thin; and none of its branches yet found bear the fructiferous stalk or spike. Its resemblance, however, to this commonest of the Lycopodia,—a plant that may be gathered by handfuls on the moors by which the flagstones are covered,—is close enough to suggest a new reading of the familiar adage on the meeting of extremes. Between the times of this ancient fossil,—one of the oldest of land plants yet known,—and those of the existing club moss that now scatters its light spores by millions over the dead and blackened remains of its remote predecessor, many creations must have intervened, and many a prodigy of the vegetable world appeared, especially in the earlier and middle periods,—Sigillaria, Favularia, Knorria, and Ulodendron,—that have had no representatives in the floras of latter times; and yet here, flanking the immense scale at both its ends, do we find plants of so nearly the same form and type, that it demands a careful survey to distinguish their points of difference. Here, for instance, to illustrate the fact, is there a specimen of Lycopodium clavatum, from one of these Caithness moors, that agrees branch for branch, and both in the disposition of its scales and in general outline, with the specimen in the stone. What seems to be an early representative of the Calamites occurs in the same beds. Some of the specimens are of large size,—at least from nine inches to a foot in circumference,—and retain their thickness, though existing as fragments several feet in length, with but little diminution throughout. They resembled the interior casts of Calamites in being longitudinally furrowed; but the furrows are flatter, and are themselves minutely striated lengthwise by lines as fine as hairs; and, instead of presenting any appearance of joints, there run diagonally across the stems, interrupted and very irregular lines of knobs. These I find referred to by Dr. Joseph Hooker, in describing a set of massive but ill preserved remains of the same organism detected in South Ness quarry, near Lerwick, by the Hon. Mr. Tuffnell, as taking, in two of the specimens, "the appearance of transverse knobs and bars (mayhap spirally arranged) that cross the striæ obliquely. But though the knobs," he adds, "may perhaps indicate a peculiar character of the plants, they have more probably been caused by pressure during silicification." As, however, they also occur in the best preserved fragment of the plant which I have yet seen,—a Thurso specimen which I owe to my friend Mr. Dick,—I deem it best to regard them, provisionally at least, as one of the characteristics of the plant. I may mention, that while I disinterred one of my specimens from the Thurso flagstones, where it occurred among remains of Dipterus and Asterolepis, I derived another specimen from the great overlying formation of pale Red Sandstone to which the lofty hills of Hoy and the tall mural precipices of Dunnet Head belong; and that this plant is the only organism which has yet been found in this uppermost member of the Lower Old Red, to at least the north of the Moray Firth. Another apparently terrestrial organism of the lower formation, of, however, rare occurrence, very much resembles a sheathing bract or spathe. It is of considerable size,—from four to six inches in length, by from two to three inches in breadth,—of a broadly elliptical and yet somewhat lanceolate form, deeply but irregularly corrugated, the rugæ exhibiting a tendency to converge towards both its lower and upper terminations, and with, in some instances, what seems to be the fragment of a second spathe springing from its base. Another and much smaller vegetable organism of the same beds presents the form of a spathe-enveloped bud or unblown flower wrapped up in its calyx; but all the specimens which I have yet seen are too obscure to admit of certain determination. I may here mention, that curious markings, which have been regarded as impressions made by vegetables that had themselves disappeared, have been detected during the last twelvemonth in a quarry of the Lower Old Red Sandstone near Huntly, by the Rev. Mr. Mackay of Rhynie. They are very curious and very puzzling; but though some of the specimens present the appearance of a continuous midrib, that throws off, with a certain degree of regularity, apparent leaflets, I am inclined to regard them rather as lying within the province of the ichnologist than of the fossil botanist. They bear the same sort of resemblance to a long, thickly-leaved frond, like that of the "hard fern," that the cast of a many-legged annelid does to a club moss; and I was struck, on my first walk along the Portobello beach, after examining a specimen kindly sent me by Mr. Mackay, to see how nearly the tract of a small shore crab (Carcinus Mænas) along the wet sand resembled them, in exhibiting what seemed to be an obscure midrib fringed with leaflets.
But the genuine vegetable organism of the formation, indicative of the highest rank of any yet found in it, is a true wood of the cone-bearing order. I laid open the nodule which contains this specimen, in one of the ichthyolite beds of Cromarty, rather more than eighteen years ago; but though I described it, in the first edition of my little work on the Old Red Sandstone, in 1841, as exhibiting the woody fibre, it was not until 1845 that, with the assistance of the optical lapidary, I subjected its structure to the test of the microscope. It turned out, as I had anticipated, to be the portion of a tree; and on my submitting the prepared specimen to one of our highest authorities,—the late Mr. William Nicol,—he at once decided that the "reticulated texture of the transverse section, though somewhat compressed, clearly indicated a coniferous origin." I may add, that this most ancient of Scottish lignites presents several peculiarities of structure. Like some of the Araucarians of the warmer latitudes, it exhibits no lines of yearly growth; its medullary rays are slender, and comparatively inconspicuous; and the discs which mottle the sides of its sap-chambers, when viewed in the longitudinal section, are exceedingly minute, and are ranged, so far as can be judged in their imperfect state of keeping, in the alternate order peculiar to the Araucarians. On what perished land of the early Palæozoic ages did this venerably antique tree cast root and flourish, when the extinct genera Pterichthys and Coccosteus were enjoying life by millions in the surrounding seas, long ere the flora or fauna of the Coal Measures had begun to be?
I may be here permitted to mention, that in a little volume, written in reply to a widely known and very ingenious work on the Development hypothesis, I described and figured this unequivocally genuine lignite, in order to show that a true wood takes its place among the earliest terrestrial plants known to the geologist. I at the same time mentioned,—desirous, of course, that the facts of the question should be fairly stated, whatever their bearing,—that the nodule in which it occurred had been partially washed out of the fish bed in which I found it, by the action of the surf; and my opponent, fixing on the circumstance, insinuated, in the answer with which he honored me, that it had not belonged to the bed at all, but had been derived from some other formation of later date. He ought, however, to have taken into account my further statement, namely, that the same nodule which enclosed the lignite contained part of another fossil, the well marked scales of Diplacanthus striatus, an ichthyolite restricted, like the Coccosteus (a specimen of which occurred in a neighboring nodule), to the Lower Old Red Sandstone exclusively. If there be any value whatever in palæontological evidence, this Cromarty lignite must have been deposited in a sea inhabited by the Coccosteus and Diplacanthus. It is demonstrable that, while yet in the recent state, a Diplacanthus lay down and died beside it; and the evidence in the case is unequivocally this, that in the oldest portion of the oldest terrestrial flora yet known, there occurs the fragment of a tree quite as high in the scale as the stately Norfolk Island pine, or the noble cedar of Lebanon.