CHAPTER IV.

Interior of the boulder Wide intervals of Geology—Illustration—Long interval between the formation of the boulder as part of a sand-bed, and its striation by glacial action—Sketch of the intervening ages—The boulder a Lower Carboniferous rock—Cycles of the astronomer and the geologist contrasted—Illustration—Plants shown by the boulder once grew green on land—Traces of that ancient land—Its seas, shores, forests, and lakes, all productive of material aids to our comfort and power—Plants of the Carboniferous era—Ferns—Tree-ferns—Calamites—Asterophyllites—Lepidodendron—Lepidostrobus—Stigmaria—Scene in a ruined palace—Sigillaria—Coniferæ, Cycadeæ—Antholites, the oldest known flower—Grade of the Carboniferous flora—Its resemblance to that of New Zealand.

I havelikened the boulder to an old volume of the middle ages encased in a modern binding. We have looked a little into the mechanism and history of the boards; in other words, we have gone over the history of the scratched surface of the boulder, of the clays and sands around it, and of that still earlier cycle of denudation whereof the rock itself is probably a relic. Before proceeding to open the volume itself, it will be well that we clearly mark the wide interval in time between the ages represented by the surface-striation and those indicated by the interior of the boulder. When we proceed from the groovings on the outside to the plants within, we pass, to be sure, over scarcely an inch of space, but we make a leap over untold millenniums in point of time. It is as if we had laid our hands on a volume of history which had by some misfortune found its way into the nursery. The first page that catches our eye relates the battle of the Reform Bill, and, on turning the previous leaf, we find ourselves with Boadicea and her woad-coloured soldiery. Now, if one utterly ignorant of the chronology of the country were to be told that the volumerelated solely to one people, he would at once see from the manners and customs delineated, that the two pages referred to very different states of civilisation, and consequently to widely-separated periods. But he could give no account of how long an interval might have elapsed between the time when London had its inhabitants massacred by Boadicea, and the time when another generation of them was excited by the tardiness of King William iv. He could form no conjecture as to what events might have happened in the meanwhile. The interval might be a century or twenty centuries, wherein the city might have been burnt down fifty times. Clearly, if he wished to make himself acquainted with the intervening history, he would have to betake himself to an unmutilated volume.

And just so is it with our boulder. We can easily believe, merely from looking at it as it lies on its clayey bed, that a long time must have elapsed between the time of its formation as part of a sandstone bed, and the period of its transportation and striation by an iceberg. The sand of which it is formed must have been washed down by currents, and other sediment would settle down over it. It would take some time to acquire its present hardness and solidity, while, in long subsequent times, after being broken up and well-rounded by breaker or current action, it may have lain on some old coast-line for centuries before it was finally frozen into an ice-floe, and so freighted to a distance. But the stone, with all its stories of the olden time, can tell us nothing of this intervening period. It leads us from a dreary frozen sea at once into a land of tropical luxuriance, and so, if we desire to know anything of the missing portion of the chronology, we must seek it elsewhere.

The Boulder-clay is one of the latest of geologic periods.[16]Beyond it we get into Tertiary times, and learn from the cavesof Yorkshire how elephants, hyenas, rhinoceroses, hippopotami, bears, and wolves, prowled over the rich valleys; while, from the quarries of the Isle of Wight, we see how at an earlier time herds of uncouth palæotheres and slimly-built anoplotheres browsed the plains of Old England. Beyond the Tertiary ages come those of the Chalk, with its ocean that swarmed with sea-urchins, terebratulæ, pectens, sponges, and many other forms. Then arises the era of the Wealden, with its bosky land haunted by the unwieldy iguanodon; the Oolite, with its land rich in a coniferous flora, and tenanted by a race of small marsupial animals, and its seas abounding in corals, encrinites of many a form, cidares, cuttle-fishes, and ammonites. Further back still, come the times of the Lias, that strange era in the history of our country, when reptiles huger than those of the Nile swam the seas, and sped on wings through the air. Then come the times of the Trias, when a vegetation still further removed from existing types clothed the land, and frogs large as oxen waddled along the shores. Then the times of the Permian, with its deep sea tenanted by a meagre list of corals and shells, and by a type of fishes that was slowly passing away. We arrive at last at the Coal or Carboniferous period, to the older ages of which our boulder belongs.

[16]For the names and succession of the rocks of which the known part of the earth's crust is composed, see the Table at the end of the volume.

These eras may have been some longer, some shorter, but each had a duration which, when tried by human standards, must be regarded as immensely protracted. The cycles of astronomy are very vast, yet I have often thought that the cycles of geology, though probably of much less duration, impress us more forcibly with the antiquity of our planet. The astronomer tells us of light that has taken two millions of years to reach our earth, and of nebulæ that are millions upon millions of miles distant, but these numbers are so vast that we cannot bring ourselves to realize them. Weknowthat there is a great difference between two millions and ten millions, but we cannot fullyappreciateit, and so theperiods of the astronomer, beyond a certain point, cease adequately to impress us. So long as they can be easily contrasted with our own standards of comparison, they have their full force; but after that, every additional million, or ten millions, or ten hundred millions, produces only a confused and bewildered sense of immensity, and the comparative amount of each addition fails to be realized. Will my reader forgive a homely illustration:—Some years ago, I stood at the pier-head of one of our smaller sea-port towns, and watched the sun as it sullenly sank behind the outline of the opposite hills. The breadth of the channel, in the direction of sunset, was several miles, but in the flush of evening one fancied he could almost have thrown a stone across. The water lay unruffled by a ripple, and reflected all the thousand varying tints that lighted up the sky. The harbour, that had been a busy scene all evening, began to grow less noisy, as one by one the herring-boats pushed out to sea. I found it not a little interesting to mark, as the boats gained the open firth, how the opposite coast-line gradually seemed to recede. The farther the dark sails withdrew, the more remote did the adjacent shores appear, until, as the last tinge of glory faded from the clouds, and a cold grey tint settled down over the landscape, the hills lay deep in shade and stretched away in the twilight as a dark and distant land from whose valleys there rose troops of stars. The coast-line, as seen in early evening, reminded me of the periods of the astronomer; as seen in early night, it reminded me of the periods of the geologist. We fail to appreciate the real duration of astronomical cycles, because they are presented to us each as one vast period. They are not subdivided into intervals, and contain no succession of events, by means of which, as by milestones, we might estimate their extent; and so their unvaried continuity tends to diminish the impression of their vastness, just as the firth, without any islet or vessel on its surface,seemed greatly narrower than it really was. For it is with time as it is with space—the eye cannot abstractly estimate distance, nor can the mind estimate duration. In either case, the process must be conducted by a comparison with known standards. The geological periods exemplify the same rule. They may not be greater, perhaps not so great, as those revealed by astronomy, yet their vastness impresses us more, because we can trace out their history, and see how step by step they progressed. Thus, that the interval between the boulder-clay and the coal-measurer was immense, we learn from the records of many successive ages that intervened, in the same way that one began to perceive the real breadth of the firth, by resting his eye on the succession of intervening herring-boats. In the former case, the mind has ever and anon a sure footing on which to pause in gauging bygone eternity; in the latter, the eye had likewise a succession of points on which to rest in measuring distance. Or, to return to a former illustration: Boadicea lived eighteen hundred years ago, but who does not feel that the last nine hundred years look a great deal longer than the first? The one set has few marked incidents to fix the thoughts; the other is replete with those of the most momentous kind. In the one, we have M meagre list of conquerors and kings, from Julius Cæsar down to Athelstan; in the other, events crowd upon us from the waning of the Saxon power down through the rising glory of our country to the present plenitude of its power and greatness. The early centuries, like the cycles of the astronomer, pass through our mind rather as one continuous period; the later centuries, like the cycles of the geologist, arrest our thoughts by a succession of minor periods, and hence the idea of duration is more vividly suggested by the diversified events of the one series, than by the comparatively unbroken continuity of the other.

Let us now open the volume and try to decipher the strangelegends which it contains. On removing some of the upper layers of the boulder, I found, as I have said, well-preserved remains of several kinds of plants. One of them was ribbed longitudinally, with transverse notches every three or four inches, us though a number of slender threads had been stretched along a rod, and tied tightly to it at regular intervals. Another, sorely mutilated, was pitted all over somewhat after the fashion in which the confectioner punctures his biscuits. A third had a more regular pattern, being prettily fretted with small lozenge-shaped prominences that wound spirally round the stalk. Other plants seemed to be present, but in a very bad state of preservation. They were all jumbled together and converted into a black coaly substance, in which no structure could be discerned.

These plants assuredly once grew green upon the land; but where now is that land on which they flourished? Had it hills and valleys, rivers and lakes, such as diversify our country? Was it tenanted by sentient beings, and, if so, what were their forms? Did insects hum their way through the air, and cattle browse on the plains, and fish gambol in the rivers? Was the land shaded with forests, dark and rugged like those of Norway, or fragrant as the orange-groves of Spain? What, in fine, were its peculiar features, and how far did its scenery resemble that of any country of the present day?

That old land has not entirely disappeared. Traces of it are found pretty extensively in South Wales, in Staffordshire, around Newcastle, and through central Scotland. Strange as it may seem, its forests are still standing in many places. The fishes that disported in its lakes, the insects that fluttered amid its woods, and the lizards that crawled among its herbage, are still in part preserved to us. Nay, more; we may sometimes see the sea-beaches of that ancient land pitted with rain-drops, and roughened with ripple-marks, as freshly as if the shower hadfallen and the tide had flowed only yesterday. The peasants along the Bay of Naples gathered grapes from the flanks of Vesuvius for well-nigh seventeen centuries, before it was ascertained that they daily walked over the site of buried cities, with temples, theatres, and private houses still erect. It was many more centuries ere the people of Great Britain discovered that not a few of their villages and towns stood on the site of buried forests, and lakes, and seas. We have now, however, become aware of the fact, and are making good use of it. We dig into the earth and exhume these old forests to supply us with light and fuel; we quarry into the ripple-marked shores which fringed that old land, and build our houses with the hardened sand; we calcine the ferruginous mud that gathered in its swampy hollows, and extract therefrom our most faithful ally both in peace and war—metallic iron; we burn the delicate corals and shells and lily-like zoophytes which lived in the sea of that far-distant era, to enable us to smelt our iron, to build our houses, and manure our fields; in short, every year we are discovering some new and valuable material in the productions of that period, or finding out some new use which can be made of the substances already known. A more than ordinary interest, therefore, attaches to the history of the land and sea which have furnished us with so many aids to comfort as well as power; and we shall find, as we go on, that that history is a very curious one.

I shall describe some of the more common plants and animals of the period, that we may be able, in some measure, to look back through the ages of the past, and see how these plants would appear when they cast their broad shadow over river and lake, and how these animals would have seemed to human eye in the twilight of the forest, in the sluggish flow of the river, and in the stagnant waters of the lagoon.

TheFlora, or vegetation of the Carboniferous era, differedwidely from any that now exists. With the exception of the highest or exogenous class, it possessed representatives of all the existing classes of the botanic scale, but in very strange proportions. The number of species of carboniferous plants already found in Great Britain amounts to about three hundred, amongst which the ferns are especially abundant. Some of them seem to have been low-growing plants, like the bracken of our hillsides, but others must have shot up to the height of forest trees. We can recognise a few coniferous and cycadaceous plants, a good many stems resembling the "horse-tail" of our marshy grounds, and some of large size akin to the creeping club-moss of our heaths; but there are still many to which there exist no living analogues.

When we examine the roof of a coal-pit, or split open plates of shale in a quarry of the coal-measures, we are struck with the similarity which the ferns in the stone bear to those among our woods and hills. One of the most common, and, at the same time, most elegant forms, is theSphenopterisor wedge-leaved fern, of which a large list of species is known. One of them (S. crenata) had a strong stem, from which there sprung straight tapering branches richly dight with leaflets. The leaflets—somewhat like minute oak-leaves—were ranged like those of our modern ferns, along two sides of the stalk, in alternate order, and tapered gently away to its outer extremity. The effect of the whole is singularly rich, and one can well believe that a garland of this ancient fern would have wreathed as gracefully around a victor's brow as the parsley of Nemea or the laurel-leaves of Delphi.

Another plant of the same genus (S. affinis,Fig. 3) has leaflets like the petals of the meadow-daisy, arranged in clusters along its slim diverging stalks. From a collection and comparison of many specimens, the late lamented Hugh Miller was enabled to make a drawing of this fern as it must have appeared when it waved green along the old carboniferous hill-sides. I enjoyedthe privilege of going over these specimens with him, and marked how, under a master-hand, piece by piece fell into its proper place, and yielded up its evidence. His restoration, which forms the frontispiece to his last work, is a very beautiful one, and it is as true as it is beautiful.

Fig. 3.Sphenopteris affinis.

Fig. 4.Pecopteris.

Fig. 5.Cyclopteris.

Fig. 6.Neuropteris.

ThePecopteris(Fig. 4,P. heterophylla) or comb-fern, is so called from its stiff thick leaflets being in some species arranged along the stalk like the teeth along the centre of a comb. Of all the plants of the coal-measures this is the one that approaches most closely to living nature. It appears to be almost identical with thepteris, of which one species is well known as the bracken of our hill-sides. Dr. Hooker figures together a frond of a New Zealand species (P. esculenta) and a fossil frond from the Newcastle pits. They are so similar as to be easily mistaken at first sight for drawings of the same plant.[17]TheNeuropteris(asN. gigantea,Fig. 6) or nerve-leaved fern, is remarkable for its strongly-defined venation. It is scarcely, perhaps, so elegant in its outline as thesphenopteris, or some of the other ferns. Its leaflets are large and thick, with an oblong or rounded form, and arranged either singly along the frond stem, or along secondary foot-stalks, which diverge from the main stem. Of the latter kind, some of the species have a good deal of resemblance to ourOsmunda regalisor royal fern. A species of the former class (N. cordata) might readily enough be mistaken for the young leaves of theScolopendriumor hart's-tongue, which hangs out its glossy green amid the gloom of dank and dripping rocks. There are, besides, several other genera of ferns in the Carboniferous strata, such as theCyclopteris(C. dilatata,Fig. 5) or round-leaved fern, and theOdontopterisor tooth-fern. Most of these seem to have been lowly plants, like the ferns ofour own country. But there was another class to which no analogue can be shown in Europe. They rose high over their humbler congeners as lofty trees, and must be studied by a reference to the existing tree-ferns of intertropical countries.

[17]Hooker,Mem. Geol. Surv.vol. ii. part ii. p. 400.

Fig. 7.Living Tree-fern.

Tree-ferns flourish in warm climates, and are met with in Brazil, the East and West Indies, New Zealand, &c. They rise sometimes to the height of fifty or sixty feet, with a longtapering stem surmounted by a dense crown of graceful fronds, and might easily be mistaken at a little distance for palms. All the known species belong to the same division (Polypodiaceæ) with the common polypodium of our road-sides. In some genera, as thealsophilaof the East Indies, the trunk is ribbed by long creeping branches, or rather rootlets, which descend to the soil, giving the tree somewhat of the appearance so often seen in old woods, where venerable fir-trees have been firmly encased by the bearded stems of the ivy. Another genus, theCyathea, has its stem covered with oblong scars where leaves were attached, and a circle of rich outspread fronds surmounts its summit. One of the coal-measure tree-ferns seems to have resembled this recent type. It is named theCaulopterisor stalk-fern, and had a thick stem picturesquely roughened by irregular oblong leaf-scars, that wound spirally from its base to its point. No specimen has hitherto been found showing the fronds in connexion with the stem, so that we are still ignorant of the kind of foliage exhibited by this ancient tree. There can be no doubt, however, that it was crowned with a large tuft of boughs that cast their shadow over the sward below, and we may, perhaps, believe that some of the numerous detached ferns found in the shales of the coal-series, once formed part of this lofty coronal.

An important section of the carboniferous plants is embraced under the generic name ofCalamites. They had smooth jointed stems, like reeds, and terminated beneath in an obtuse curved point (Fig. 8), from which there sprang broad leaflets or rather rootlets. After many years of research our knowledge of these plants is still very scanty. Some of them have exhibited a highly-organized internal structure, from which it appears that they consisted—first, of a soft central cellular pith; second, of a thick layer of woody tissue; and third, an external cylinder of strong bark, ribbed longitudinally, and furrowed transversely.They have been ranked with the common horse-tail of our ponds, but they would rather appear to belong to a higher family. The breadth of the stem is very various, some specimens being a foot or more in diameter, others scarcely half an inch. From the discoveries of Professor Williamson and Mr. Binny of Manchester, it seems not unlikely that what we call calamites may be really the inner core of a plant not yet named, just as a set of fossils were long calledsternbergiæ, before they were discovered to be really the pith of coniferous trees. With regard to the branches of the calamites, Brongniart's conjecture may be true, that they exist among the group of plants calledasterophyllites. It is not unlikely that many dissimilar plants have been grouped together as calamites, and, on the other hand, that plants allied to the typical species have been thrown into separate genera. For it requires but a slight acquaintance with the vegetable kingdom to know how many forms analogous parts of the same plant may assume, and how impossible it would often be to guess the real relationship of such varieties if they were not found growing together on one plant.

Fig. 8.Terminal portion of a calamite stem.

Fig. 9.[18]

[18]The fossil given inFig. 9is named by Lindley (Foss. Flo.t. 15, 16),Calamites nodosus. He admits, however, that it was not found in actual contact with a calamite stem. It has exactly the contour of an asterophyllite, and might, perhaps, be referred to that genus. It is inserted here that the reader may see the general form of the asterophyllites, and the close relationship that subsists between these plants and the calamites.

A remarkably graceful class of the coal-plants are known asasterophyllites. They had slim fluted and jointed stalks, apparently of humble growth. From each of the joints there sprang two thin opposite branches with stellate clusters of leaflets arranged round them at equal distances. If the reader will take a young rush-stalk, and string along it a number of the flowers of the little star-wort, keeping them a little distance apart, he may form some idea of the appearance of a single branch of the star-bearingasterophyllite. Some of the plants embraced under this genus are conjectured to have been aquatic, spreading out their clusters of leaflets in the green sluggish water of stagnant pools; but many of them are evidentlyrelated to the calamites, and may possibly have formed part of these plants.

Whoever has rambled much in a coal-country, scrambling through briars and brambles in old quarries, or threading his way among the rocks of river-courses, must often have noticed, on the exposed surface of sandstone blocks, dark ribbon-like bands fretted over with little diamond-shaped knobs. They are so common in some districts, that you can scarcely light upon a piece of sandstone which does not show one or more. They belong to a carboniferous plant known aslepidodendron(Fig. 10) or scaly tree, from the peculiar style of ornamentation which adorned its bark. Its structure and affinities have puzzled botanists not a little. A well-preserved specimen reminds one of the appearance presented by a twig of the Scotch fir, when stripped of its green spiky leaflets. The scars thus left at the base of the leaflets are of a wedge-like form, and run spirally up the branch in a manner very like those on the branches of lepidodendron; and it was accordingly supposed at one time that the latter plant belonged, or at least was allied, to the conifers. But the branches of lepidodendron possessed a peculiarity that is shared in by none of our present coniferous trees. They were what botanists calldichotomous,—that is, they subdivided into two equal branches, these again into other two, and so on. Their internal texture,[19]too, differed from that of any known conifer. The only tribe of existing plants with which the lepidodendron seems to bear comparison, are theLycopodiaceæ, or club-mosses, of which we have several species in the moor-lands of our own country. They are low trailing plants, with moss-like scaly branches, bearing at their ends shaggy little tufts, whence the popular name of the genus. In warmer climates, they are both more numerous and attain a larger size, sometimes standing erect to about the height of an ordinary gooseberry-bush. But though the lepidodendron appears tohave been allied to these plants in structure, it greatly differed from them in dimensions. The club-mosses of the coal-measures shot up as goodly trees, measuring fifty feet and upwards in height, and sometimes nearly five in diameter. Their general effect must have been eminently picturesque. A shaggy covering of green spiky leaflets bristled over their multitudinous pendant boughs; and where on the older stems these leaflets had decayed and dropped off, the outer bark was laid bare, fretted over with rows of diamond-shaped or oval scars, separated by waving lines of ridge or furrow, that wound spirally round the stem. From not a few of the branches there sprang oblong hirsutecones calledlepidostrobi(Fig. 11), which bore the sporangia, or seed-cases. These cones are of frequent occurrence in the shales of the coal-measures, and may be readily recognised. They had a central axis round which the oblong sporangia were built, the whole being protected externally by a thick covering of pointed scales, imbricated like the cone of the Scotch fir. The leaflets of lepidodendron, calledlepidophylla, were broader than those of the Scotch fir, and had a stout mid-rib, which must have given them a rigidity like that of the araucarian pine a plant they may also have resembled in the dark glossy green of its leaves.

[19]See Hooker,Mem. Geol. Surv.vol. ii. part ii. p. 436.

Fig 10.Lepidodendron Sternbergii.

Fig. 11.Lepidostrobus.

Of all the common coal-measure plants, there is perhaps none so abundant as that known by the name ofstigmaria, or punctured-stem. It is found spreading out its rootlets for several yards in beds of shale and under-clay, and sometimes even limestone,[20]while, in many sandstones, fragments of its blackened stems lie as thickly strewn as twigs among the woods in autumn. I have said that several of the plants above described have greatly puzzled botanists. None of them, perhaps, has given rise to so much conjecture and variety of opinion as the stigmaria. The history of the discussion regarding its nature and affinities, would be not a little interesting as an illustration of the slow hindered progress often attendant on the researches of science, and an instance of how a few simple facts are sometimesenough to overturn the most plausible theories and probable conjectures. Many thousands of specimens had been examined ere one was found that revealed the true nature of the stigmaria. It was by some imagined to be a soft succulent marshy plant, consisting of a number of long branches radiating from a sort of soft disk, like spokes from the centre of a wheel. Analogies were suggested with dicotyledonous tribes, as thecactiandeuphorbiæ, though it was at the same time admitted that the ancient plant presented appearances which seemed very anomalous.

[20]The fresh-water limestone of Mid-Calder abounds in long trailing stems and rootlets of stigmaria, mingled with other terrestrial plants, and shells ofcyprides.

Fig. 12 Stigmaria rootlets springing from Sigillaria stem.

In the course of an extensive survey of the coal-field of South Wales, Mr. (now Sir William) Logan ascertained the important fact, that each coal-seam is underlaid by a bed of clay, in which the stems of stigmaria, branching freely in all directions, may be traced to the distance of many feet or even yards. They were recognised as undoubtedly occupying the site on which they grew, and consequently each coal-seam was held to rest upon an ancient soil. Some years afterwards, in making a cutting for the Lancaster and Bolton Railway, several upright massive stems belonging to a plant calledsigillaria, were found to pass downwards into true stigmaria stems (Fig. 12). There could be no doubt that they were different parts of one and the same plant. This fact has since been abundantly demonstrated from the Nova Scotia coal-field. Many sigillariæ have been found there passing down into the fire-clay below, where they branch out horizontally as true stigmatiæ. It is evident, therefore, that the stigmaria was the under-ground portion of a plant, which, judging from the nature of the soil, and the free mode inwhich the tender rootlets branched off, appears to have lived in aquatic or marshy stations.

Fig. 13.Stigmaria.

The stigmaria is too well marked to be readily confounded with any other coal-measure plant. It had a rounded stem, seldom more than four or five inches across, which was markedby a series of circular tubercules with a puncture in the centre, arranged in spiral lines round the stem. Each of these tubercules is surrounded, in ordinary specimens, by a circular depression,[21]and the whole plant (if one may use the comparison) looks as if it had been smitten with small-pox. From the hollow in the centre of each protuberance, there shot out a long round rootlet, formerly thought to be a leaf, and since the tubercules are pretty thickly set, the stigmaria must have had a somewhat hirsute appearance as it crept through the mud. It would resemble a thick bearded stem of ivy, save that the fibres, instead of running up two sides, were clustered all round it. Along the centre of the root, there ran a woody pith of a harder and more enduring texture than the surrounding part of the plant. The space between the outer tuberculed rind and the inner pith, seems to have been of a soft cellular nature, and to have decayed first, for the pith is sometimes hollow, and may not unfrequently be seen at a distance from the centre, and almost at the outer bark—a circumstance that seems only explicable on the supposition, that while the surrounding portions were decaying, the firmer pith altered its position in the hollow stem, sinking to the lower side, if the plant lay prostrate, and that it did not itself begin to decay until the interior of the stem had been at least partially filled up with sand or mud, or fossilized by the infiltration of lime. From the root of the sigillaria, which has a curious cross-shaped mark on its base,the stems of stigmaria strike out horizontally, first as four great roots which subdivide as they proceed. Their subdivisions are dichotomous, each root splitting equally into two, and thus they want that intricate interlacing of rootlet which is so familiar to us. The whole disposition of these under-ground stems is singularly straight and regular, leading us to believe that they shot out freely through a soft muddy soil.

[21]Such is the usual aspect of the plant. But as the stems have been, for the most part, greatly flattened by the pressure of the superincumbent rocks, the sharpness of the pattern has been much effaced. In some specimens described by Dr. Hooker, as having been found in an upright position, the external ornamentation presents an appearance somewhat different. What in the common specimens stand out as tubercules, are there seen to be deep circular cavities, in which the shrunk flagon-shaped bases of the rootlets are still observable. (See above,Fig. 13b, which is taken from one of Dr. Hooker's plates. For a detailed description of the structure of stigmaria, see the paper above referred to in theGeological Survey Memoirs.) A very ornate species is mentioned by the late Hugh Miller, in which each tubercule formed the centre of a sculptured star, and the whole stem seemed covered over with flowers of the composite order. And what is, perhaps, still more curious, the stem was seen to end off 7 in an obtuse point, tuberculed like the rest of the plant.—Testimony of the Rocks, p. 461.

Some time ago I chanced to visit the remains of what had once been a royal residence, and still looked majestic even in decay. It gave a saddened pleasure to thread its winding stairs, and pass dreamily from chamber to hall, and chapel to closet; to stand in its gloomy kitchens, with their huge fire-places, whose blackened sides told of many a roaring fagot that had ruddied merry faces in days long gone by; to creep stealthily into the sombre dungeons, so dank, earthy, and cold, and then winding cautiously back, to emerge into the light of the summer sun. The silent quadrangle had its encircling walls pierced with many a window, some of which had once been richly carved; but their mullions were now sorely wasted, while others, with broken lintels and shattered walls above, seemed only waiting for another storm to hurl them among the roofless chambers below. In the centre of the court-yard stood a ruined fountain. It had been grotesquely ornamented with heads of lions and griffins, and was said to have once run red with wine. But it was silent enough now; the hand of time, and a still surer enemy, the hand of man, had done their worst upon it; its groined arches and foliaged buttresses were broken and gone, and now its shattered beauty stood in meet harmony with the desolation that reigned around. I employed myself for a while in looking over the fragments, marking now the head of some fierce hippogryph, anon the limbs of some mimic knight clad in armour of proof, and ere long I stumbled on a delicately sculpturedfleur-de-lis, that might have surmounted the toilet-window of some fair one of old. Turning it over, I found its unhewn side exhibited a still more delicately sculptured stigmaria. Theincident was certainly simple enough, perhaps even trifling. And yet, occurring in a spot that seemed consecrated to reverie, it awoke a train of pleasant reflection. How wide the interval of time which was bridged across in that sculptured stone! Its one side carried the mind back but a few generations, the other hurried the fancy away over ages and cycles far into the dim shadows of a past eternity. The one told of a land of flowers, musical with the hum of the bee and the chantings of birds, and gladdened by the presence of man; the other told of a land luxuriant, indeed, in strange forms of vegetation—huge club-mosses, tall calamites, and waving ferns—yet buried in a silence that was only broken fitfully by the breeze as it shook the spiky catkins or the giant fronds of the forest. Thefleur-de-lisrecalled memories of France—the sunny land of France—which stood out so brightly in the dreams of our school-days; the stigmaria conjured up visions of a land that was never gazed on by human eye, but rolled its rich champaign during the long ages of the Carboniferous era, and sometimes rises up dimly in the dreams of our maturer years. Between these two epochs how many centuries, how many cycles must have slowly rolled away! Thefleur-de-liswas carved but yesterday; the stigmaria flourished when the earth was young, and had seen scarcely a third part of its known history.

I have said that the stem of the stigmaria is called sigillaria. The name may be translatedsignet-stem,[22]and has reference to one of the distinguishing peculiarities of the plant. About twenty British species are enumerated, some of them very dissimilar, yet they all agree in having long fluted stems with parallel rows of prominent seal-like tubercules. The sigillaria differed so widely in its whole contour and ornamentation from every living plant, that it is impossible to convey an idea of its formby reference to existing vegetation. Some of the species, asS. organum(Fig. 14), had their trunks traversed longitudinally by broad ridges separated by narrow furrows. Along the summit of each ridge there ran a line of tubercules, set regularly at distances varying from a third or a quarter of an inch to close contact. One may sometimes see no unfair representation of the bark of this ancient tree, when looking at a newly ploughed field in spring-time, having each of its broad ridges dotted with a row of potato sacks. Other species, while exhibiting the same plan, differed not a little in the details. In some the tubercules are round, in others angular, and in a third set double or kidney-shaped. In some they are far apart, in others they are strung together like a chain of beads. Sometimes they exist as mere specks, while occasionally they broaden out so as to equal in width the ridge that supports them. One species (S. reniformis), instead of the broad ridge and narrow furrow, exhibits an arrangement exactly the reverse. It looks not unlike a cast of the species first described, save that its broad flat furrows support rows of much larger tubercules. The breast of a lady's chemisette, with a thick-set row of buttons down each plait, would be somewhat like this species of sigillaria, with this difference, however, that the buttons on the plant were of a form that does not appear as yet to have come into fashion among the fair sex. Yet they had no little elegance, and like many other objects in the geological storehouse, might be a useful model for our students of design. They were neither round nor quite oval, but rather of a kidney-shape, or like a double cherry.

[22]The word sigillaria is really plural, and was used by the Romans to denote the little images which friends were wont to present to each other at the end of the Saturnalia. They answered pretty nearly to christmas-boxes and new year's gifts among ourselves. It is not uninteresting thus to find among the hard dry names of science, one that two thousand years ago was synonymous with all the kindliness of friendship.

Fig. 14.Sigillaria, with black carbonized bark partially removed.

There can be no doubt that these tubercules must once have supported leaflets. They are true leaf-scars, like those on the Scotch fir, and the lozenge-shaped knobs on the bark of lepidodendron. But of the form of these leaves we are still in ignorance, for no part of the plant, save the stem and roots, has yet been found. The sigillaria must have been a tree that could not long withstand maceration, for not only are its leaves gone, but, in many cases, the outer bark has partially or wholly decayed, leaving a scarcely distinguishable mass of carbonized matter.[23]When this outer rind is peeled off, the inner surface of the stem is seen to be ridged, furrowed, and tuberculed in the same way, but the markings are much less distinct than on the outside. The bark sometimes attains the thickness of an inch, and is always found as a layer of pure coal enveloping the stem where it stands erect, or lying as a flat cake without any central cylinder where the stem is prostrate. (SeeFig. 14.)

[23]Another proof of the looseness of the texture of this ancient vegetable may be gathered from the almost invariable truncation of even the largest erect stems; they are snapped across at the height of a few feet from their base. The famous "Torbanehill Mineral" contains many such fragmentary stems, often of considerable thickness. Their interior consists of the same material as the surrounding bed, and displays many dissevered plants that may have been washed into the decaying trunks. For the internal structure of sigillaria see Dr Hooker'sMemoir, and the authorities therein cited.

Another remarkable feature in this carboniferous plant is that it appears to have had no branches along its stem. Trunks have been found four and five feet in diameter, and have been traced to a distance of fifty, sixty, and even seventy feet, without any marks of branches being detected. Brongniart examined the portion of one stem, which, at its thicker end, had been broken across, but still measured a foot in breadth. It ran for forty feet along the gallery of a mine, narrowing to a width of not more than six inches, when it divided into two, each branchmeasuring about four inches across. The sigillaria stems, accordingly, must have shot up, slim and straight, to a height of sometimes seventy feet before they threw out a single branch. We know nothing of the coronal of these strangely-formed trees. From Brongniart's observations, it would seem that the upper part of the stem, like that of the lepidodendron, was dichotomous, that is, it branched out into two minor stems; but how these were disposed is unknown. We are wholly ignorant, too, of the foliage of these branches, though, from the general structure of the plant, as well as from the number of fern-fronds often found around the base of the stems, it has been conjectured that the sigillaria was cryptogamous, and, like the tree-ferns, supported a group of sweeping fronds. If so, it differed in many respects from every known member of the cryptogamic tribes.

Putting together, then, all that we know of the exterior of the sigillaria, we find that it was a tall slender tree, with, palm-like, a clump of foliaged branches above, its stem bristling thickly, in at least its upper part, with spiky leaves, and its roots equally hirsute, shooting out to a distance of sometimes forty feet through the soft muddy soil. Future researches may bring us better acquainted with this ancient organism. In the meanwhile, enough of it is known to mark it out as one of the most ornate forms of vegetation that the world has ever seen.

In addition to the above, the coal strata have yielded many other fragmentary remains, to which names have been given, but of which very little is known. It is pleasant, amid such a wide sea of doubt and uncertainty, to alight upon some well-known form of whose affinities there can be no question, since it still finds its representatives in living nature. Of such a kind are the coniferous stems occasionally met with in the sandstones of the coal-measures. .

It is now many years since the operations of the quarryman in the carboniferous sandstones of Edinburgh and Newcastle disclosed the remains of huge gnarled trunks deeply imbeddedin the rock. The neighbourhood of the latter town yielded, in 1829,[24]the stem of a tree seventy-two feet long, without branches, but roughened with numerous knobs, indicative of the places whence branches had sprung. At Craigleith, near Edinburgh, a trunk thirty-six feet long, and three feet in diameter at the base, was disinterred in the year 1826. Since then, several others have been found in the same neighbourhood; some of them sixty and even seventy feet in length, and from two to six in breadth. They were, for the most part, stripped of roots and branches, and lay at a greater or less angle among the white sandstone beds, which they cut across obliquely. It was unknown for some time to what division of the vegetable kingdom these trunks should be referred. Their irregular branched surface and undoubted bark indicated a higher kind of structure than that possessed by any of the other carboniferous plants; but the conjecture remained unverified until an ingenious and beautiful method was discovered of investigating their internal organization. Two Edinburgh geologists, Mr. Nichol and Mr. Witham, succeeded in obtaining slices of the plants sufficiently transparent to be viewed under the microscope by transmitted light, and in this way their true structure was readily perceived. The method of preparing these objects was simply as follows:—A thin slice of the plant to be studied was cut by the lapidary, or detached by the hammer. One side having been ground down smooth, and polished, was cemented by Canada balsam to a piece of plate-glass, and the upper surface was then ground down and polished in like manner, so as to leave the slice no thicker than cartridge-paper.[25]When the preparation was then placed under a magnifying power, the minute cells and woody fibre of the plant could be detected as clearly as those of a recent tree. The Craigleith fossils were in this way recognised as belonging tothe great coniferous family, and to that ancient[26]division of it which is, at the present day, represented by the pine of Norfolk Island—"a noble araucarian, which rears its proud head from 160 to 200 feet over the soil, and exhibits a green and luxuriant breadth of foliage rare among the coniferæ."[27]Some of these plants have yielded faint traces of the annual rings shown so markedly in the cross section of our common forest-trees; whence it would appear, that even as far back as the times of the coal-measures, there were seasons of alternate heat and cold, though probably less defined than now.

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