THE STORY OF A BOULDER.
THE STORY OF A BOULDER
OR
GLEANINGS FROM THE NOTE-BOOK OF A
FIELD GEOLOGIST
BY
ARCHIBALD GEIKIE
OF THE GEOLOGICAL SURVEY OF GREAT BRITAIN.
Illustrated with Woodcuts.
EDINBURGH: THOMAS CONSTABLE AND CO.
HAMILTON, ADAMS, AND CO., LONDON.
MDCCCLVIII.
EDINBURGH: T. CONSTABLE, PRINTER TO HER MAJESTY.
TO
GEORGE WILSON, M.D., F.R.S.E.
REGIUS PROFESSOR OF TECHNOLOGY IN THE
UNIVERSITY OF EDINBURGH,
THESE PAGES
ARE
AFFECTIONATELY INSCRIBED.
PREFACE
The present Volume has been written among the rocks which it seeks to describe, during the intervals of leisure of a field-geologist. Its composition has been carried on by snatches, often short and far apart, some of the descriptions having been jotted down on the spot by streamlet and hill-side, or in the quiet of old quarries; others, again, in railway-carriage or stage-coach. By much the larger portion, however, has been written by the village fireside, after the field-work of the day was over—a season not the most favourable to any mental exercise, for weariness of body is apt to beget lassitude of mind. In short, were I to say that these Chapters have been as often thrown aside and resumed again as they contain paragraphs, the statement would probably not exceed the truth. But the erratic life of an itinerant student of science is attended with yet greater disadvantages. It entails an absence from all libraries, more especially scientific ones, and the number of works of reference admissible into his parva supellex must ever be few indeed. With these hindrances, can the writer venture to hope that what has thus been so disjointed and unconnected to him, will not seem equally so to his readers? Yet if his descriptions, written, as it were, face to face with Nature, are found to have caught some tinge of Nature's freshness, and please the reader well enough to set him in the way of becoming a geologist, he shall have accomplished all his design.
It cannot be too widely known, or too often pressed on the attention, especially of the young, that a true acquaintance with science, so delightful to its possessors, is not to be acquired at second-hand. Text-books and manuals are valuable only so far as they supplement and direct our own observations. A man whose knowledge of Nature is derived solely from these sources, differs about as much from one who betakes himself to Nature herself, as a dusty, desiccated mummy does from a living man. You have the same bones and sinews in both; but in the one they are hard and dry, wholly incapable of action; in the other they are instinct with freshness and life. He who would know what physical science really is, must go out into the fields and learn it for himself: and whatever branch he may choose, he will not be long in discovering that a forenoon intelligently spent there must be deemed of far more worth than days and weeks passed among books. He sees the objects of his study with his own eyes, and not through "the spectacles of books;" facts come home to him with a vividness and reality they never can possess in the closet; the free buoyant air brightens his spirits and invigorates his mind, and he returns again to his desk or his workshop with a store of new health and pleasure and knowledge. Geology is peculiarly rich in these advantages, and lies in a manner open to all. No matter what may be the season of the year, it offers always some material for observation. In the depth of winter we have the effects of ice and frost to fall back upon, though the country should lie buried in snow; and then when the longer and brighter days of spring and summer come round, how easily may the hammer be buckled round the waist, and the student emerge from the dust of town into the joyous air of the country, for a few delightful hours among the rocks; or when autumn returns with its long anticipated holidays, and preparations are made for a scamper in some distant locality, hammer and note-book will not occupy much room in the portmanteau, and will certainly be found most entertaining company. The following pages—forming a digest of the Carboniferous rocks—may, perhaps, in some measure, guide the explorations of the observer, by indicating to him the scope of geological research, the principles on which the science rests, and the mode in which it is pursued. But I repeat, no book, no lecture-room, no museum, will make a geologist of him. He must away to the fields and study for himself, and the more he can learn there he will become the better geologist.
He need not burden himself with accoutrements. A hammer, pretty stout in its dimensions, with a round blunt face and a flat sharp tail; a note-book and a good pocket-lens, are all he needs to begin with. Having these, let him seek to learn the general characters' of the more common rocks, aiding himself, where he can, by a comparison with the specimens of a museum, or, failing that, with the descriptions of a text-book. Let him then endeavour to become acquainted with some of the more characteristic fossils of the district in which he resides, so as to be able to recognise them wherever they occur. Private collections and local museums are now becoming comparatively common, and these, where accessible, will aid him vastly in his studies. Having at length mastered the more abundant rocks and organic remains of his neighbourhood, let him try to trace out the connexion of the different strata across the country, so as to understand its structure. For this purpose it will be necessary to examine every ravine and natural exposure of the rocks, along with quarries, ditches, railway-cuttings, and, in short, the whole surface of the district. A general notion of the geology of the place will, not perhaps be of very difficult attainment; and this done, the observer should attempt to put down the connexion of the rocks on paper, for till this is accomplished he will have at the best but an imperfect, and perhaps incorrect notion of the subject. The best map of the district should be obtained, also a clinometer, or instrument for ascertaining the angle at which rocks dip with the horizon, and a pocket-compass with which to mark the direction of the dip and strike of strata, that is, the outcrop, or line which they form when they come to the surface. Thus armed, he may commence a geological survey of his neighbourhood. Wherever he sees a bed of rock exposed, it should be marked down on his map with an arrow pointing to the direction in which the stratum is dipping, the angle of dip, ascertained by the clinometer, being put alongside. The nature of the rock, whether sandstone, shale, limestone, or greenstone, must be set down at the same place, and, to save room, a system of marks for the different rocks may be conveniently used. When a sufficient area of ground has been thus traversed, the student may find, say a row of arrows on his map all pointing due west, and indicating a set of quarries about a quarter of a mile distant from one another, the rock in each of them dipping to the west. If there be at the one end a limestone containing certain fossils, and at the other end a stratum exactly similar, containing the same fossils, while the quarries between display the same rock, he will infer, of course, that the whole is one limestone, and will accordingly draw a line from the last quarry on the north to the last on the south, connecting them all together. If the bed dips steeply down, the line will be narrower,—if but slightly inclined, it will be broader; the breadth of such a line (which may be coloured to taste) always varying with the thickness of the stratum and the angle which it makes with the horizon. In a district where faults and curvatures along with trap-rocks abound, the mapping becomes more complex, but the principle remains the same—a curved stratum on the ground making a similarly curved band on the map, and a fault or dislocation of a set of beds producing, in the same way, a corresponding break in the lines traced. In short, a geological map should be as far as possible a transcript of the surface rocks of a country. The beginner should avoid, however, attempting too much; it will be enough for him at first to have mastered the leading features of the geology of his district; the details cannot be shown save on a map of a large scale, and are better transferred to his note-book. The use of such mapping is to enable us to gain a correct knowledge of the geological structure of a country, and of the relation of rocks to each other as regards age, origin, &c. Bacon tells us that "writing makes an exact man;" we may say with equal truth that mapping makes an exact geologist. It is sometimes easy enough to obtain a notion of the general character of a district by taking a few rambles across it; but we can never know it thoroughly until we have mapped it. And this is done not as mere dry routine, or by a series of hard uninteresting rules. In reading off the geological structure of a country, we ascertain its history during many thousand ages long prior to that of man. We become, as it were, interpreters of hieroglyphics, and historians of long-perished dynasties.
Those who have had experience of field-geology, know how vain it is to attempt to compress into a page or two the results of years, and that a few vague general directions are about the utmost that can be attempted. The practice of the science cannot be taught in books, far less in prefaces, neither can it be learned from them. And so I once more repeat the advice: Get away to the fields. Seek to decipher the geological records for yourself, and look with your own eyes into the long series of ages whose annals lie inscribed among the rocks. If you can secure the co-operation of a few companions, so much the better. Half-a-dozen hammers zealously at work in a richly fossiliferous stratum will soon pile up a tolerable collection of its treasures. But whether singly or in company, use your eyes and your hammer, and even though in the end you should never become a geologist, you will in the meantime gain health and vigour, and a clearness of observation, that will stand you in good stead through life.
CONTENTS.
CHAPTER I.
PAGE
Scene near Colinton in midsummer—A grey travelled Boulder—Its aspect and contents—Its story of the past,
CHAPTER II.
Exterior of the boulder—Travelled stones a difficult problem—Once referred to the Deluge—Other theories—Novelty of the true solution—Icebergs formed in three ways—Progress and scenery of an iceberg—Its effects—Size of icebergs—Boulder clay had a glacial origin—This explanation confirmed by fossil shells—Laws of the distribution of life—Deductions,
CHAPTER III.
How the boulder came to be one—"Crag and tail"—Scenery of central Scotland: Edinburgh—"Crag and tail" formerly associated in its origin with the boulder-clay—This explanation erroneous—Denudation an old process—Its results—Illustration from the Mid-Lothian coal-field—The three Ross-shire hills—The Hebrides relics of an ancient land—Scenery of the western coast—Effects of the breakers—Denudation of the Secondary strata of the Hebrides—Preservative influence of trap-rocks—Lost species of the Hebrides—Illustration—Origin of the general denudation of the country—Illustrative action of streams—Denudation a very slow process—Many old land-surfaces may have been effaced—Varied aspect of the British Islands during a period of submergence—Illustration,
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,
CHAPTER V.
Scenery of the carboniferous forests—Contrast in the appearance of coal districts at the present day—Abundance of animal life in the Carboniferous era—Advantages of palæontology over fossil-botany—Carboniferous fauna—Actiniæ—Cup-corals—Architecture of the present day might be improved by study of the architecture of the Carboniferous period—Mode of propagation of corals—A forenoon on the beach—Various stages in the decomposition of shells—Sea-mat—Bryozoa—Fenestella—Retepora—Stone-lilies—Popular superstitions—Structure of the stone-lilies—Aspect of the sea-bottom on which the stone-lilies flourished—Sea-urchins—Crustacea, their high antiquity—Cyprides—Architecture of the Crustacea and mollusca contrasted—King-crabs,
CHAPTER VI.
Carboniferous fauna continued—George Herbert's ode on "Man"—His idea of creation—What nature teaches on this subject—Molluscous animals—Range of species in time proportionate to their distribution in space—Two principles of renovation and decay exhibited alike in the physical world and the world of life—Their effects—The mollusca—Abundantly represented in the carboniferous rocks—Pteropods—Brachiopods—Productus—Its alliance with Spirifer—Spirifer—Terebratula—Lamellibranchs—Gastropods—Land-snail of Nova Scotia—Cephalopods—Structure of orthoceras—Habits of living nautilus,
CHAPTER VII.
Classification of the naturalist not always correspondent with the order of nature—Incongruous grouping of animals in the invertebrate division—Rudimentary skeleton of the cephalopods—Introduction of the vertebrate type into creation—Ichthyolites of the carboniferous rocks—Their state of keeping—Classification of fossil fishes—Placoids—Ichthyodorulites—Ganoids—Their structure exemplified in the megalichthys and holoptychius—Cranium of megalichthys—Its armature of scales—Microscopic structure of a scale—Skeleton of megalichthys—History of the discovery of the holoptychius—Confounded with megalichthys—External ornament of holoptychius—Its jaws and teeth—Microscopic structure of the teeth—Paucity of terrestrial fauna in coal measures—Insect remains—Relics of reptiles—Concluding summary of the characters of the Carboniferous fauna—Results,
CHAPTER VIII.
Sand and gravel of the boulder—What they suggested—Their consideration leads us among the more mechanical operations of Nature—An endless succession of mutations in the economy of the universe—Exhibited in plants In animals—In the action of winds and oceanic currents—Beautifully shown by the ceaseless passage of water from land to sea, and sea to land—This interchange not an isolated phenomenon—How aided in its effects by a universal process of decay going on wherever a land surface is exposed to the air—Complex mode of Nature's operations—Interlacing of different causes in the production of an apparently single and simple effect—Decay of rocks—Chemical changes—Underground and surface decomposition—Carbonated springs—The Spar Cave—Action of rain-water—Decay of granite—Scene in Skye—Trap-dykes—Weathered cliffs of sandstone—Of conglomerate—Of shale—Of limestone—Caverns of Raasay—Incident—Causes of this waste of calcareous rocks—Tombstones,
CHAPTER IX.
Mechanical forces at work in the disintegration of rocks—Rains—Landslips—Effects of frosts—Glaciers and icebergs—Abrading power of rivers—Suggested volume on the geology of rivers—Some of its probable contents—Scene in a woody ravine—First idea of the origin of the ravine one of primeval cataclysms—Proved to be incorrect—Love of the marvellous long the bane of geology—More careful examination shows the operations of Nature to be singularly uniform and gradual—The doctrine of slow and gradual change not less poetic than that of sudden paroxysms—The origin of the ravine may be sought among some of the quieter processes of Nature—Features of the ravine Lessons of the waterfall—Course of the stream through level ground—True history of the ravine—Waves and currents—What becomes of the waste of the land—The Rhone and the Leman Lake—Deltas on the sea-margin—Reproductive effects of currents and waves—Usual belief in the stability of the land and the mutability of the ocean—The reverse true—Continual interchange of land and sea part of the economy of Nature—The continuance of such a condition of things in future ages rendered probable by its continuance during the past,
CHAPTER X.
The structure of the stratified part of the earth's crust conveniently studied by the examination of a single formation—A coal-field selected for this purpose—Illustration of the principles necessary to such an investigation—The antiquities of a country of value in compiling its pre-historic annals—Geological antiquities equally valuable and more satisfactorily arranged—Order of superposition of stratified formations—Each formation contains its own suite of organic remains—The age of the boulder defined by this test from fossils—Each formation as a rule shades into the adjacent ones—Mineral substances chiefly composing the stratified rocks few in number—Not of much value in themselves as a test of age—The Mid-Lothian coal-basin—Its subdivisions—The limestone of Burdiehouse—Its fossil remains—Its probable origin—Carboniferous limestone series of Mid-Lothian—Its relation to that of England—Its organic remains totally different from those of Burdiehouse—Structure and scenery of Roman Camp Hill—Its quarries of the mountain limestone—Fossils of these quarries indicative of an ancient ocean-bed—Origin of the limestones—Similar formations still in progress—Coral-reefs and their calcareous silt—Sunset among the old quarries of Roman Camp Hill,
CHAPTER XI.
Intercalation of coal seams among mountain limestone beds of Mid-Lothian—North Greens seam—Most of our coal seams indicate former land-surfaces—Origin of coal a debated question—Erect fossil trees in coal-measures—Deductions to be drawn therefrom—Difference between the mountain limestone of Scotland and that of England—Coal-bearing character of the northern series—Divisions of the Mid-Lothian coal-field—The Edge coals—Their origin illustrated by the growth of modern deltas—Delta of the Nile—Of the Mississippi—Of the Ganges—Progress of formation of the Edge coals—Scenery of the period like that of modern deltas—Calculations of the time required for the growth of a coal-field—Why of doubtful value—Roslyn Sandstone group—Affords proofs of a general and more rapid subsidence beneath the sea—Its great continuity—Probable origin—Flat coals—Similar in origin to the Edge coals below—Their series not now complete—Recapitulation of the general changes indicated by the Mid-Lothian coal-field,
CHAPTER XII.
Trap-pebbles of the boulder—Thickness of the earth's crust unknown—Not of much consequence to the practical geologist—Interior of the earth in a highly heated condition—Proofs of this—Granite and hypogene rocks—Trap-rocks: their identity with lavas and ashes—Scenery of a trappean country—Subdivisions of the trap-rocks—Intrusive traps—Trap-dykes—Intrusive sheets—Salisbury Crags—Traps of the neighbourhood of Edinburgh—Amorphous masses—Contemporaneous trap-rocks of two kinds—Contemporaneous melted rocks—Tests for their age and origin—Examples from neighbourhood of Edinburgh—Tufas or volcanic ashes—Their structure and origin—Example of contemporaneous trap-rocks—Mode of interpreting them—Volcanoes of Carboniferous times—Conclusion,
THE STORY OF A BOULDER.
CHAPTER I.
Scene near Colinton in midsummer—A grey travelled Boulder—Its aspect and contents—Its story of the past.
Three miles to the south-west of Edinburgh, and not many hundred yards from the sequestered village of Colinton, there is a ravine, overshaded by a thick growth of beech and elm, and traversed beneath by a stream, which, rising far away among the southern hills, winds through the rich champaign country of Mid-Lothian. It is, at all seasons of the year, one of the most picturesque nooks in the county. I have seen it in the depth of winter—the leafless boughs doddered and dripping, the rocks dank and bare save where half-hidden by the rotting herbage, and the stream, red and swollen, roaring angrily down the glen, while the families, located along its banks, fleeing in terror to the higher grounds, had left their cottages to the mercy of the torrent. The last time I visited the place was in the heart of June, and surely never did woodland scene appear more exquisitely beautiful. The beech trees were in full leaf, and shot their silvery boughs in slender arches athwart the dell, intertwining with the broader foliage and deeper green of the elm, and the still darker spray of the stately fir. The rocks on either side were tapestried with verdure; festoons of ivy, with here and there a thread of honey-suckle interwoven, hung gracefully from the cliffs overhead; each projecting ledge had its tuft of harebells, or speedwell, or dog-violets, with their blue flowers peeping out of the moss and lichens; the herb-robert trailed its red blossoms over crag and stone; the wood-sorrel nestled its bright leaves and pale flowerets among the gnarled roots of beech and elm; while high over all, alike on the rocks above and among the ferns below, towered the gently drooping stalks of the fox-glove. The stream, almost gone, scarcely broke the stillness with a low drowsy murmur, as it sauntered on among the lapides adesos of its pebbly channel. Horace's beautiful lines found again their realization:—
"Qua pinus ingens, albaque populus
Umbram hospitalem consociare amant
Ramis, et obliquo laborat
Lympha fugax trepidare rivo." [1]
Where the tall pine and poplar pale
Delight to cast athwart the vale
A pleasing shade.
While the clear stream low murmuring bells.
And o'er its winding channel toils
Adown the glade.—A. G.
It was noon, and the sun shone more brightly and with greater heat than had been felt for years. The air, heavy and warm, induced a feeling of listlessness and languor, and the day seemed one for which the only appropriate employment would have been to read once again the "Castle of Indolence." But failing that, I found it pleasant to watch the flickering light shot in fitful gleams through the thick canopy of leaves, and thus, in the coolness of the shade, to mark these rays—sole messengers from the sweltering world around—as they danced from rock to stream, now lighting up the ripples that curled dreamily on, now chequering some huge boulder that lay smooth and polished in mid-channel, anon glancing playfully among the thickets of briar or honeysuckle and vanishing in the shade. Sometimes a wagtail would alight at hand, or a bee drone lazily past, while even an occasional butterfly would venture down into this shady covert. But, with these exceptions, the animal creation seemed to have gone to sleep, an example which it was somewhat difficult to avoid following. While thus idly engaged, my eye rested on a large boulder on the opposite side. It lay partly imbedded in a stiff clay, and partly protruding from the surface of the bank some way above the stream. A thick arbour of leafage overhung it, through which not even the faintest ray of sunshine could force its way. The spot seemed cooler and more picturesque than that which I occupied, and so, crossing the well-nigh empty channel, I climbed the bank and was soon seated on the boulder. A stout hammer is a constant companion in my rambles, and was soon employed on this occasion in chipping almost unconsciously the newly-acquired seat. The action was, perhaps, deserving of the satire of Wordsworth's Solitary:—
"You may trace him oft
By scars, which his activity has left
Beside our roads and pathways, though, thank Heaven!
This covert nook reports not of his hand.
He, who with pocket-hammer smites the edge
Of luckless rock or prominent stone, disguised
In weather-stains, or crusted o'er by Nature
With her first growths, detaching by the stroke
A chip or splinter to resolve his doubts;
And, with that ready answer satisfied,
The substance classes by some barbarous name,
And hurries on; or from the fragments picks
His specimen; if but imply interveined
With sparkling mineral, or should crystal cube
Lurk in its cells and thinks himself enriched.
Wealthier, and doubtless wiser, than before!"
There was nothing in the distant aspect of the boulder to attract attention. It was just such a mass as dozens of others all round. Nor, on closer inspection, might anything peculiar have been observed. It had an irregularly oblong form, about two or three feet long, and half as high. Ferns and herbage were grouped around it, the wood-sorrel clustered up its sides, and little patches of moss and lichen nestled in its crevices. And yet, withal, there was something about it that, ere long, riveted my attention. I examined it minutely from one end to the other, and from top to bottom. The more I looked the more did I see to interest me; and when, after a little labour, some portions of its upper surface were detached, my curiosity was abundantly gratified. That grey lichened stone, half hid among foliage, and unheeded by any human being, afforded me material for a pleasant forenoon's thought. Will my reader accept an expanded narrative of my reverie?
I can almost anticipate a smile. "What can there be remarkable in such a grey stone, hidden in a wood, and of which nobody knows anything? It never formed part of any ancient building; it marks the site of no event in the olden time; it is linked with nothing in the history of our country. What of interest, then, can it have for us?" Nay, I reply, you are therein mistaken. It is, assuredly, linked with the history of our country—it does mark the passing of many a historical event long ere human history began; and, though no tool ever came upon it, it did once form part of a building that rose under the finger of the Almighty during the long ages of a bygone eternity. To change the figure, this boulder seemed like a curious volume, regularly paged, with a few extracts from older works. Bacon tells us that "some books are to be tasted, others to be swallowed, and some few to be chewed and digested." Of the last honour I think the boulder fully worthy, and if the reader will accompany me, I shall endeavour to show him how the process was attempted by me.
The rock consisted of a hard grey sandstone finely laminated above, and getting pebbly and conglomeritic below. The included pebbles were well worn, and belonged to various kinds of rock. The upper part of the block was all rounded, smoothed, and deeply grooved, and, when split open, displayed numerous stems and leaflets of plants converted into a black coaly substance. These plants were easily recognisable as well-known organisms of the carboniferous strata, and it became accordingly evident that the boulder was a block of carboniferous sandstone. The pebbles below, however, must have been derived from more ancient rocks, and they were thus seen to represent some older geological formation. In this grey rock, therefore, there could at once be detected well-marked traces of at least two widely-separated ages. The evidence for each was indubitable, and the chronology of the whole mass could not be mistaken. The surface striation bore undoubted evidence of the glacial period, the embedded plants as plainly indicated the far more ancient era of the coal-measures, while the pebbles of the base pointed, though dimly, to some still more primeval age. I had here, as it were, a quaint, old, black-letter volume of the middle ages, giving an account of events that were taking place at the time it was written, and containing on its earlier pages numerous quotations from authors of antiquity. The scratched surface, to complete the simile, may be compared to this old work done up in a modern binding. Let us, then, first of all, look for a little at the exterior of the volume, and inquire into the origin of that strangely-striated surface, and of the clay in which the boulder rested.
CHAPTER II.
Exterior of the boulder—Travelled stones a difficult problem—Once referred to the Deluge—Other theories—Novelty of the true solution—Icebergs formed in three ways—Progress and scenery of an iceberg—Its effects—Size of icebergs—Boulder-clay had a glacial origin—This explanation confirmed by fossil shells—Laws of the distribution of life—Deductions.
Has the reader, when wandering up the course of a stream, rod in hand perhaps, ever paused at some huge rounded block of gneiss or granite damming up the channel, and puzzled himself for a moment to conjecture how it could get there? Or when rolling along in a railway carriage, through some deep cutting of sand, clay, and gravel, did the question ever obtrude itself how such masses of water-worn material came into existence? Did he ever wonder at the odd position of some huge grey boulder, far away among the hills, arrested as it were on the steep slope of a deep glen, or perched on the edge of a precipitous cliff, as though a push with the hand would hurl it down into the ravine below? Or did he ever watch the operations of the quarryman, and mark, as each spadeful of soil was removed, how the surface of the rock below was all smoothed, and striated, and grooved?
These questions, seemingly simple enough, involve what was wont to be one of the greatest problems of geology, and not many years have elapsed since it was solved. The whole surface of the country was observed to be thickly covered with a series of clays, gravels, and sands, often abounding in rounded masses of rock of all sizes up to several yards in diameter. These deposits were seen to cover all the harder rocks, and to occur in a very irregular manner, sometimes heaped up into great mounds, and sometimes entirely wanting. They were evidently the results of no agency visible now, either on the land or around our coasts. They had an appearance rather of tumultuous and violent action, and so it was wisely concluded that they must be traces of the great deluge. The decision had at least this much in its favour, it was thoroughly orthodox, and accordingly received marked approbation, more especially from those who wished well to the young science of geology, but were not altogether sure of its tendencies. But, alas! this promising symptom very soon vanished. As observers multiplied, and investigations were carried on in different countries, the truth came out that these clays and gravels were peculiarly a northern formation; that they did not appear to exist in the south of France, Italy, Asia Minor, Syria, and the contiguous countries. If, then, they originated from the rushing of the diluvian waters, these southern lands must have escaped the catastrophe, and the site of the plains of Eden would have to be sought somewhere between the Alps and the North Pole. This, of course, shocked all previous ideas of topography; it was accordingly agreed, at least among more thoughtful men, that with these clays and sands the deluge could have had nothing to do.
Other theories speedily sprang up, endeavouring to account for the phenomena by supposing great bodies of water rushing with terrific force across whole continents, sweeping away the tops of hills, tearing up and dispersing entire geological formations, and strewing the ocean-bottom with scattered debris. But this explanation had the disadvantage of being woefully unphilosophical and not very clearly orthodox. Such debacles did not appear to have ever taken place in any previous geologic era, and experience was against them. Besides, they did not account for some of the most evident characteristics of the phenomena, such as the northern character of the formation, the long parallel striations of the rock surfaces, and the perching of huge boulders on lofty hills, often hundreds of miles distant from the parent rock. Geologists were completely at fault, and the boulder-clay remained a mystery for years.
When we consider the physical aspects of the countries where the question was studied, we cannot much wonder that the truth was so hard to find. In the midst of corn-fields and meadows, one cannot readily realize the fact that the spot where they stand has been the site of a wide-spread sea; and that where now villages and green lanes meet the eye, there once swam the porpoise and the whale, or monsters of a still earlier creation, unwieldy in bulk and uncouth in form. Such changes, however, must have been, for their traces meet us on every hand. We have the sea dashing against our shores, and there seems nothing at all improbable in the assertion that once it dashed against our hill-tops. No one, therefore, has any difficulty in giving such statements his implicit belief. But who could have dreamed that these fields, so warm and sunny, were once sealed in ice, and sunk beneath a sea that was cumbered with many a wandering iceberg? Who could have imagined, that down these glens, now carpeted with heath and harebell, the glacier worked its slow way amid the stillness of perpetual snow? And yet strange as it may seem, such is the true solution of the problem. The boulder-clay was formed during the slow submergence of our country beneath an icy sea, and the rock-surfaces owe their polished and striated appearance to the grating across them of sand and stones frozen into the bottom of vast icebergs, that drifted drearily from the north. That we may the better see how these results have been effected, let us glance for a little at the phenomena observable in northern latitudes at the present day.
Icebergs are formed in three principal ways:—1st, By glaciers descending to the shore, and being borne seawards by land-winds; 2d, By river-ice packed during spring, when the upper reaches of the rivers begin to thaw; 3d, By coast-ice.
I. There is an upper stratum of the atmosphere characterized by intense cold, and called the region of perpetual snow. It covers the earth like a great arch, the two ends resting, one on the arctic, the other on the antarctic zone, while the centre, being about 16,000 feet above the sea,[2] rises directly over the tropics. Wherever a mountain is sufficiently lofty to pierce this upper stratum, its summit is covered with snow, and, as the snow never melts, it is plain that, from the accumulations of fresh snow-drifts, the mountain-tops, by gradually increasing in height and width, would become the supporting columns of vast hills of ice, which, breaking up at last from their weight and width, would roll down the mountain-sides and cover vast areas of country with a ruin and desolation more terrible than that of any avalanche. Olympus would really be superposed upon Ossa. By a beautiful arrangement this undue growth is prevented, so that the hill-tops never vary much in height above the sea. The cone of ice and snow which covers the higher part of the mountain, sends down into each of the diverging valleys a long sluggish stream of ice, with a motion so slow as to be almost imperceptible. These streams are called glaciers. As they creep down the ravines and gorges, blocks of rock detached by the frosts from the cliffs above, fall on the surface of the ice, and are slowly carried along with it. The bottom also of the glaciers is charged with sand, gravel, and mud, produced by the slow-crushing movement; large rocky masses become eventually worn down into fragments, and the whole surface of the hard rock below is traversed by long parallel grooves and striæ in the direction of the glacier's course. Among the Alps, the lowest point to which the glacier descends is about 8500 feet. There the temperature gets too high to allow of its further progress, and so it slowly melts away, choking up the valleys with piles of rocky fragments called moraines, and 'giving rise to numerous muddy streams that traverse the valleys, uniting at length into great rivers such as the Rhone, which enters the Lake of Geneva turbid and discoloured with glacial mud.
[2] The average height of the snow-line within the tropics is 15,207 feet, but it varies according to the amount of land and sea adjacent, and other causes. Thus, among the Bolivian Andes, owing to the extensive radiation, and the ascending currents of air from the neighbouring plains and valleys, the line stands at a level of 18,000 feet, while, on mountains near Quito, that is, immediately on the equatorial line, the lowest level is 15,795.—See Mrs. Somerville's Physical Geography, 4th edit. p. 314.
In higher latitudes, where the lower limit of the snow-line descends to the level of the sea, the glaciers are often seen protruding from the shore, still laden with blocks that have been carried down from valleys far in the interior. The action of storms and tides is sufficient to detach large masses of the ice, which then floats off, and is often wafted for hundreds of miles into temperate regions, where it gradually melts away. Such floating islands are known as icebergs.
II. In climates such as that of Canada, where the winters are very severe, the rivers become solidly frozen over, and, if the frost be intense enough, a cake of ice forms at the bottom. In this way sand, mud, and rocky fragments strewing the banks or the channel of the stream, are firmly enclosed. When spring sets in, and the upper parts of the rivers begin to thaw, the swollen waters burst their wintry integuments, and the ice is then said to pack. Layer is pushed over layer, and mass heaped upon mass, until great floes are formed. These have often the most fantastic shapes, and are borne down by the current, dropping, as they go, the mud and boulders, with which they are charged, until they are stranded along some coast line, or melt away in mid-ocean.
III. But icebergs are also produced by the freezing of the water of the ocean. In high latitudes, this takes place when the temperature falls to 28·5° of Fahrenheit. The surface of the sea then parts with its saline ingredients, and takes the form of a sheet of ice, which, by the addition of successive layers, augmented sometimes by snow-drifts, often reaches a height of from thirty to forty feet. On the approach of summer these ice-fields break up, crashing into fragments with a noise like the thundering of cannon. The disparted portions are then carried towards the equator by currents, and may be encountered by hundreds floating in open sea. Their first form is flat, but, as they travel on, they assume every variety of shape and size.
On the shores of brackish seas, such as the Baltic, or along a coast where the salt water is freshened by streams or snow-drifts from the land, sheets of ice also frequently form during severe frosts. Sand and boulders are thus frozen in, especially where a layer of ice has formed upon the sea-bottom.[3] The action of gales or of tides is sufficient to break up these masses, which are then either driven ashore and frozen in a fresh cake of ice, or blown away to sea. The bergs formed in this way have originally a low flat outline, and many extend as ice-fields over an area of many miles, while, at a later time, they may be seen towering precipitously as great hills, some 200 or 300 feet high.
[3] I was informed by the late Mr. Hugh Miller, that a seam of shale abounding in liassic fossils, had been found intercalated among the boulder-clay beds in the vicinity of Eathie. He explained its occurrence there by supposing that it had formed a reef along a shore where ground-ice was forming; and so having been firmly frozen in, it was torn up on the breaking of the ice, and deposited at a distance among the mud at the sea-bottom.
Few sights in nature are more imposing than that of the huge, solitary iceberg, as, regardless alike of wind and tide, it steers its course across the face of the deep far away from land. Like one of the "Hrim-thursar," or Frost-giants of Scandinavian mythology,[4] it issues from the portals of the north armed with great blocks of stone. Proudly it sails on. The waves that dash in foam against its sides shake not the strength of its crystal walls, nor tarnish the sheen of its emerald caves. Sleet and snow, storm and tempest, are its congenial elements. Night falls around, and the stars are reflected tremulously from a thousand peaks, and from the green depths of "caverns measureless to man." Dawn again arises, and the slant rays of the rising sun gleam brightly on every projecting crag and pinnacle, as the berg still floats steadily on; yet, as it gains more southern latitudes, what could not be accomplished by the united fury of the waves, is slowly effected by the mildness of the climate. The floating island becomes gradually shrouded in mist and spume, streamlets everywhere trickle down its sides, and great crags ever and anon fall with a sullen plunge into the deep. The mass becoming top-heavy, reels over, exposing to light rocky fragments still firmly imbedded. These, as the ice around them gives way, are dropped one by one into the ocean, until at last the iceberg itself melts away, the mists are dispelled, and sunshine once more rests upon the dimpled face of the deep.[5] If, however, before this final dissipation, the wandering island should be stranded on some coast, desolation and gloom are spread over the country for leagues. The sun is obscured, and the air chilled; the crops will not ripen; and, to avoid the horrors of famine, the inhabitants are fain to seek some more genial locality until the ice shall have melted away; and months may elapse before they can return again to their villages.
[4] The account of the origin of these giants, as given in the prose Edda, is very graphic, and may be not inaptly quoted here:—"When the rivers that are called Elivagar had flowed far from their sources," replied Har, "the venom which they rolled along; hardened, as does dross that runs from a furnace, and became ice. When the rivers flowed no longer, and the ice stood still, the vapour arising from the venom gathered over it and froze to rime; and in this manner were formed in Ginnungagap many layers of congealed vapour, piled one over the other."—"That part of Ginnungagap," added Jafnhar, "that lies towards the north, was thus filled with heavy masses of gelid vapour and ice, whilst everywhere within were whirlwinds and fleeting mists. But the southern part of Ginnungagap was lighted by the sparks and flakes that flew into it from Muspellheim.... When the heated blast met the gelid vapour, it melted into drops, and, by the might of him who sent the heat, these drops quickened into life, and took a human semblance. The being thus formed was named Ymir, from whom descend the race of the Frost-giants (Hrim-thursar), as it is said in the Völuspá, 'From Vidolph came all witches; from Vilmeith all wizards; from Svarthöfdi all poison-seekers; and all giants from Ymir.'"—See Mallet's Northern Antiquities, edit. Bohn, p. 402.
[5] That beautiful expression of Æschylus occurs to me, so impossible adequately to clothe in English: ἁνηριθμον γελασμα κυματων. Who that has spent a calm summer day upon the sea, has not realized its force and delicate beauty?
The iceberg melts away, but not without leaving well-marked traces of its existence. If it disappear in mid-ocean, the mud and boulders, with which it was charged, are scattered athwart the sea-bottom. Blocks of stone may thus be carried across profound abysses, and deposited hundreds of miles from the parent hill; and it should be noticed, that this is the only way, so far as we know, in which such a thing could be effected. Great currents could sweep masses of rock down into deep gulfs, but could not sweep them up again, far less repeat this process for hundreds of miles. Such blocks could only be transported by being lifted up at the one place and set down at the other; and the only agent we know of, capable of carrying such a freight, is the iceberg. In this way, the bed of the sea in northern latitudes must be covered with a thick stratum of mud and sand, plentifully interspersed with boulders of all sizes, and its valleys must gradually be filled up as year by year the deposit goes on.
But this is not all. The visible portion of an iceberg is only about one-ninth part of the real bulk of the whole mass, so that if one be seen 100 feet high, its lowest peak may perhaps be away down 800 feet below the waves. Now it is easy to see that such a moving island will often grate across the summit and along the sides of submarine hills; and when the lower part of the berg is roughened over with earth and stones, the surface of the rock over which it passes will be torn up and dispersed, or smoothed and striated, while the boulders imbedded in the ice will be striated in turn.
But some icebergs have been seen rising 300 feet over the sea; and these, if their submarine portions sank to the maximum depth, must have reached the enormous total height of 2700 feet—that is, rather higher than the Cheviot Hills.[6] By such a mass, any rock or mountain-top existing 2400 feet below the surface of the ocean would be polished and grooved, and succeeding bergs depositing mud and boulders upon it, this smoothed surface might be covered up and suffer no change until the ocean-bed should be slowly upheaved to the light of day. In this way, submarine rock surfaces at all depths, from the coast line down to 2000 or 3000 feet, may be scratched and polished, and eventually entombed in mud.
[6] In the American Journal of Science for 1843, p. 155, mention is made of an iceberg aground on the Great Bank of Newfoundland. The average depth of the water was about 500 feet, and the visible portion of the berg from 50 to 70 feet high, so that its total height must have been little short of 600 feet, of which only a tenth part remained above water.
Fig. 1. Iceberg grating along the sea-bottom and depositing mud and boulders.
And such has been the origin of the deep clay, which, with its included and accompanying boulders, covers so large a part of our country. When this arctic condition of things began, the land must have been slowly sinking beneath the sea; and so, as years rolled past, higher and yet higher zones of land were brought down to the sea-level, where floating ice, coming from the north-west, stranded upon the rocks, and scored them all over as it grated along. This period of submergence may have continued until even the highest peak of the Grampians disappeared, and, after suffering from the grinding action of ice-freighted rocks, eventually lay buried in mud far down beneath a wide expanse of sea, over which there voyaged whole argosies of bergs. When the process of elevation began, the action of waves and currents would tend greatly to modify the surface of the glacial deposit of mud and boulders, as the ocean-bed slowly rose to the level of the coast line. In some places the muddy envelope was removed, and the subjacent rock laid bare, all polished and grooved. In other localities, currents brought in a continual supply of sand, or washed off the boulder mud and sand, and then re-deposited them in irregular beds; hence resulted those local deposits of stratified sand and gravel so frequently to be seen resting over the boulder clay. At length, by degrees, the land emerged from the sea, yet glaciers still capped its hills and choked its valleys; but eventually a warmer and more genial climate arose, plants and animals, such as those at present amongst us, and some, such as the wolf, no longer extant, were ere long introduced; and eventually, as lord of the whole, man took his place upon the scene.[7]
[7] The reader who wishes to enter more fully into the geological effects of icebergs, should consult the suggestive section on that subject in De la Beche's Geological Observer; also the Principles and Visit to the United Stales of Sir Charles Lyell, with the various authorities referred to by these writers.
It is pleasant to mark, when once the true solution of a difficulty is obtained, how all the discordant elements fall one by one into order, and how every new fact elicited tends to corroborate the conclusion. In some parts of the glacial beds, there occur regular deposits of shells which must have lived and died in the places where we find them. From ten to fifteen per cent, of them belong to species which are extinct, that is to say, have not been detected living in any sea. Some of them are still inhabitants of the waters around our coasts, but the large majority occur in the northern seas. They are emphatically northern shells, and get smaller in size and fewer in number as they proceed southward, till they disappear altogether. In like manner, the palm, on the other hand, is characteristically a tropical plant. It attains its fullest development in intertropical countries, getting stunted in its progress towards either pole, and ceasing to grow in the open air beyond the thirty-eighth parallel of latitude in the southern hemisphere, and the forty-fifth in the northern. So, too, the ivy, which in our country hangs out its glossy festoons in every woodland, and around the crumbling walls of abbey, and castle, and tower, is nursed in the drawing-rooms of St. Petersburg as a delicate and favourite exotic. In short, the laws which regulate the habitat of a plant or an animal are about as constant as those which determine its form. There are, indeed, exceptions to both. We may sometimes find a stray vulture from the shores of the Mediterranean gorging itself on sheep or lambs among the wolds of England,[8] just as we often see
"A double cherry seeming parted,
But yet an union in partition;"
or as we hear of a sheep with five legs, and a kid with two heads. But these exceptions, from their comparative rarity, only make the laws more evident. When, therefore, we find, in various parts of our country, beds of shells in such a state of preservation as to lead us to believe that the animals must have lived and died where their remains are now to be seen, we justly infer that the districts where they occur must at one period have been submerged. If the shells belong to fresh-water species, it is plain that they occur on the site of an old lake. If they are marine, we conclude that the localities where they are found no matter how high above the sea must formerly have stood greatly lower, so as to form the ocean bed. To proceed one step further. If the shells are of a southern type, that is, if they belong to species[9] which are known to exist only in wanner seas than our own, we pronounce that at a former period the latitudes of Great Britain must have enjoyed a more temperate and genial climate, so as to allow southern shells to have a wider range northwards. If, on the other hand, they are of an arctic or boreal type, we in the same way infer that our latitudes were once marked by a severer temperature than they now possess, so as to permit northern shells to range farther southwards. This reasoning is strictly correct, and the truth involved forms the basis of all inquiries into the former condition of the earth and its inhabitants.
[8] Two of these birds (Neopron pecnopterus) are stated to have been seen near Kilve, in Somersetshire, in October 1825. One was shot, the other escaped.
[9] There is not a little difficulty in reasoning satisfactorily as to climatal conditions, from the distribution of kindred forms. Even in a single genus there may be a wide range of geographical distribution, so that mere generic identity is not always a safe guide. Thus, the elephant now flourishes in tropical countries, but in the glacial period a long-haired species was abundant in the frozen north. I have above restricted myself entirely to species whose habits and geographical distribution are already sufficiently known.
The evidence furnished by the northern shells in the boulder-clay series is, accordingly, of the most unmistakable kind. These organisms tell us that at the time they lived our country lay sunk beneath a sea, such as that of Iceland and the North Cape, over which many an iceberg must have journeyed, and thus they corroborate our conclusions, derived independently from the deep clay and boulder beds and the striated rock-surfaces, as to the glacial origin of the boulder-clay.
CHAPTER III.
How the boulder came to be one "Crag and tail"—Scenery of central Scotland: Edinburgh—"Crag and tail" formerly associated in its origin with the boulder-clay—This explanation erroneous—Denudation an old process—Its results—Illustration from, the Mid-Lothian coal-field—The three Ross-shire hills—The Hebrides relics of an ancient land—Scenery of the western coast—Effects of the breakers—Denudation of the Secondary strata of the Hebrides—Preservative influence of trap-rocks—Lost species of the Hebrides—Illustration—Origin of the general denudation of the country—Illustrative action of streams—Denudation a very slow process—Many old land-surfaces may have been effaced—Varied aspect of the British Islands during a period of submergence—Illustration.
The scratched and grooved surface of the boulder was produced when it was fast frozen in some iceberg, and driven gratingly across some submarine summit, or stranded on some rocky coast-line. But, from its rounded form, the stone had evidently undergone a long process of wear and tear previous to its glacial journey. Probably it had hitherto lain along a surf-beaten beach, where in the course of ages it had gradually been worn into its present rounded shape. But how came it there? It must originally have formed part of a flat sandstone bed, with many other beds piled above it. By what agency, then, was this great pile reduced to fragments?
The answer to these questions must be a somewhat lengthened one, for the subject relates not to a few beds of rock hastily broken up and dispersed, but to the physical changes of an entire country, carried on during a vast succession of geological periods.
A phenomenon, known familiarly as "crag and tail," has long been connected in its origin with the drift or boulder beds. Has my reader ever travelled through central Scotland? If so, he must often have noticed the abrupt isolated form of many of the hills, presenting a mural front to the west, and a long sloping declivity to the east. From the great number of isolated hard trap-rocks in this region, the phenomenon is much better seen than in most other parts of the kingdom. There is, for instance, the castle rock of Stirling, with its beetling crag and castellated summit, which present so imposing a front to the west. Many other examples are seen along the line of the Edinburgh and Glasgow Railway. The range of hills south of Linlithgow, the singularly abrupt basalt of Binny Craig, the long rounded ridge of Ratho, the double-peaked crag of Dalmahoy, the broad undulation of woody Corstorphine, are all examples more or less marked. Edinburgh itself is an excellent illustration. The Calton Hill shows a steep front to the town, while its eastern side slopes away down to the sea. Arthur's Seat, in like manner, has a precipitous western face, and a gentle declivity eastward. The Castle rock, too, shoots up perpendicularly from the valley that girdles it on the north, west, and south, sinking away to the east in a long slope—
"Whose ridgy back heaves to the sky,
Piled deep and massy, close and high."
East-Lothian presents several well-marked instances; in particular, North Berwick Law and Traprain. A phenomenon so general must have had some general origin, and it was accordingly attributed to the same agency which produced the drift-clays and the striated rock-surfaces, when these were believed to be the results of great diluvial action. It would seem, however, that the phenomenon of crag and tail should not be associated with the boulder-clay. The latter is undoubtedly a newer Tertiary formation,[10] but the denudation[11] which produced crag and tail must have been going on long ere the Tertiary ages had begun. There is satisfactory evidence that large areas of our country were planed down at a greatly more ancient period than that of even the oldest of the Tertiary series. Thus, the whole area of the county of Sussex suffered a very extensive denudation during the later Secondary ages. The Hebrides had undergone a similar process previous to the deposition of the Lias and Oolite, and the Greywacke hills of south Scotland, previous to the formation of the Old Red Sandstone. There seems thus to have been a general and continuous process of degradation at work during a long succession of geological ages.
[10] The reader is referred to the table of the geological formations at the end of the volume for the relative position of the beds described.
[11] Denudation is a geological term used to denote the removal of rock by the wasting action of water, whereby the underlying mineral masses are denuded or laid bare.
The results of this long-continued action are of the most startling kind. I have referred to the phenomenon of crag and tail as perhaps the most readily observable. We must not fail to remember that the crag which now stands up so prominently above the level of the surrounding country, at one period lay buried beneath an accumulation of sandstone, shale, or other strata, all of which have been carried away, so as to leave the harder rock in bold relief, with a portion of the less coherent strata sloping as a long tail from its eastern side. The crag, too, is often breached in many places, worn down at one end, rounded on the summit, and sometimes well-nigh ground away altogether, whilst in front there is invariably a deep hollow scooped out by the current when arrested by the abrupt cliff. In [Fig. 2, a] represents a crag of greenstone worn away and bared of the shales which once covered it; b, the sloping "tail" of softer strata, protected from abrasion by the resistance of the trap-rock, and covered by a deep layer of drift, d; c marks the hollow on the west side of the crag.
Fig. 2 "Crag and tail."
But when we come to measure the actual amount of material that has been carried away, we are lost in conjecture as to the vastness of the time which such a process must have occupied. For instance, the coal-bearing strata of Mid-Lothian must at one period have been connected with those of Linlithgow and Stirling. At a subsequent date, the western area subsided to form the Stirlingshire coal-basin, and the eastern area, in like manner, sank down to form the coal-basin of Mid-Lothian, while the intermediate portion stretched from east to west as a great arch, or, as it is termed geologically, an anticlinal axis. Now, the whole of this arch has been worn away, not a vestige of it remains, and yet its upper or coal-bearing part was fully 3000 feet thick.[12]
[12] This remarkable example of denudation was first described by Mr. M'Laren, in his Sketch of the Geology of Fife and the Lothians, a work in which the author showed himself to be in advance of the science of his time.
Let us take a small portion of this district, and endeavour to calculate the amount of matter thus removed. The Pentland hills form a chain stretching from near Edinburgh for some fourteen miles southward, and having an average breadth of about two miles and a half. They are formed chiefly of felspathic trap-rocks, resting upon and interstratified with conglomerate apparently of Old Red age, which in turn lies upon vertical Silurian slates. Before the Carboniferous strata were thrown down by successive faults, they must have covered these hills completely to a depth of not less than 6000 feet.[13] From this small area, therefore, stratified sandstones, shales, limestones, and coal, must have been removed to the enormous extent of one billion, eight hundred and fifty-four thousand, four hundred and sixty-four millions of cubic feet.
[13] The actual depth of the Mid-Lothian coal-field, to the base of the carboniferous limestone, is rather more than 3000 feet. It is, perhaps, rather under than over the truth to allow 3000 feet for the total thickness of beds from the limestone to the conglomerate of Liberton, though, owing to the curved and contorted position of the strata from Edinburgh to Stirlingshire, it is impossible to obtain a measurement of their real thickness. I have attributed the isolation of the Falkirk and Mid-Lothian coal-fields to the effect of faults and general depressions of their areas. This was assuredly the case in the latter coal-field, and probably in the former also. The trap which occurs between them, though in great abundance, has certainly not acted as an elevating agent. It occurs in beds among the strata, and, judging from the number of associated tufas, appears to have been to a considerable extent erupted while the lower carboniferous series was forming. Mr. M'Laren, in his excellent work, p. 100, states his opinion that the traps may have materially contributed to push up the coal strata. A careful and extended examination of the district has convinced me that this view is incorrect.
But, perhaps, the most striking instances of denudation in the British Islands are the three famous Ross-shire hills—Suil Veinn, Coul Mor, and Coul Bheig. They are formed of piles of sandstone beds like tiers of regular masonry, and reach a height of 3000 feet over the sea. The sandstone of which they are composed must once have formed a bed or set of beds fully 2000 feet thick, that covered the whole district for many miles around. Yet of this extensive deposit there now exist only a few isolated fragments. I have watched the sunshine and shadow of an autumn sky resting alternately on these strange pyramidal hills, as they towered in their giant proportions like the last remnants of a mighty rampart that had stood the brunt of a long siege, and, breached at last in many places, had been all but levelled to the ground. How long-continued and how potent must that agency have been which could cut down and disperse the massive barrier that flanked the western coast of Ross-shire to a height of 2000 feet!
The Hebrides are but the shattered relics of an old land that had its mountain-peaks and its glens, its streams and lakes, and may have nursed in its solitude the red-deer and the eagle, but was never trodden by the foot of man. A glance at the map is enough to convince us of this. We there see islands, and peninsulas, and promontories, and deep bays, and long-retiring inlets, as though the country had been submerged and only its higher points remained above water. The conviction is impressed more strongly upon us by a visit to these shores. We sail through the windings of one of the "sounds," and can scarcely believe that we are on the bosom of the salt sea. Hills rise on all sides, and the water, smooth as a polished mirror, shows so pure and limpid that in the sunshine we can see the white pebbles that strew its bed many fathoms down. The eastern shore is often abruptly interrupted by long-receding lochs edged round with lofty mountains, and thus, where we had looked to see a deep heathy glen, with, perchance, a white tree-shaded mansion in the far distance, and a few dun smoking cottages in front, we are surprised to catch a glimpse of the white sails of a yacht, or the darker canvas of the herring-boats. We sail on, and soon a sudden turn brings us abruptly to the mouth of the sound. A bold headland, studded around with rocky islets, rises perpendicularly from the sea, bleak and bare, without a bush or tree, or the faintest trace of the proximity of man. The broad swell of the Atlantic comes rolling in among these rocks, and breaks in foam against the grey cliffs overhead. In tempests, such a scene must be of the most terrific kind. Wo to the hapless vessel that is sucked into the vortex of these breakers, whose roar is sometimes heard at the distance of miles! Even in the calmest weather the white surf comes surging in, and a low sullen boom is ever reverberating along the shore. We see the harder rocks protruding far into the sea, and often pierced with long twilight caves, while the softer ones are worn into deep clefts, or hollowed out into open bays strewed over with shingle. The sunken rocks and islets, scarcely showing their tops above water, were all evidently at one time connected, for, as we recede from the shore, we can mark how the process of demolition goes on. There is first the projecting ness or promontory, well-nigh severed from the mainland, but still connected by a rude arch, through which the swell ever gurgles to and fro. Then, a little farther from the shore, a huge isolated crag, washed on all sides by the surge, raises its grey lichen-clothed summit. A short way beyond, there is the well-worn islet whose surface shelters neither lichen nor sea-weed, but is ever wet with the dash of the waves. Further to the sea, the white gleam of the breakers marks the site of the sunken rock. Thus, in the space of a hundred yards, we may sometimes behold the progress of change from land to sea, and see before us a specimen of that action which slowly but yet steadily has narrowed and breached the outline of our western shores.[14]
[14] I have endeavoured to illustrate the process of denudation by a reference to breaker-action on the existing coast-line of the Hebrides; but a strong current must have materially increased the force of the ancient waves, and produced abrasion to some depth below them.
If we attempt to trace the connexions of strata among the Hebrides, we shall be more fully impressed with the magnitude of the changes which have been effected. Thus the Lias and Oolite occur in patches along the shores of Mull, Morven, Ardnamurchan, Eigg, Skye, Raasay, and Applecross. But though now only in patches, these formations must once have extended over a considerable area, for they seem to form the under-rock of the whole of the northern part of Skye, and are seen in almost every lone island from Ardnamurchan Point to the Shiant Isles. These scattered portions, often many miles distant from each other, are the remnants of a great sheet of liassic and oolitic strata, now almost entirely swept away, and are extant from having been covered over with hard trap-rocks. But for these it may be doubted whether we should ever have known that corals once gleamed white along the shores of Skye, that the many-chambered ammonite swam over the site of the Coolin Hills, that the huge reptilian monsters of these ancient times, icthyosaurs and plesiosaurs, careered through the waters that laved the grey hills of Sleat, and that forests of zamia and cycas, and many other plants indicative of a warm climate, bloomed green and luxuriant along the site of that strange mist-clad cliff-line, that shoots up into the pinnacles of the Storr and Quiraing. It is curious to reflect, that the records of these peaceful scenes have been preserved to us by the devastating eruptions of volcanic forces; that the old lava-streams which spread death through the waters along whose bed they travelled, have yet been the means of protecting the districts which they wasted, while those parts where they did not reach have been long since swept away. It is allowable to believe, that in the portions of liassic strata which have been destroyed there existed the remains of not a few species, perhaps some genera, to be found nowhere else, and of whose former existence there is now, by consequence, no trace. In the small island of Pabba—a relic of the Scottish Lias—I found thirty-one species, of which Dr. Wright has pronounced four to be new.[15] A subsequent visit to the adjacent island of Raasay has increased the list. In short, every patch of these Secondary rocks, if thoroughly explored, might be found to yield its peculiar organisms. And in the far larger area that has been carried away there existed, doubtless, many more. We are accustomed to see individuals perish and their remains crumble away, but the species still holds on. In the stratified portion of the earth's crust, however, we mark how not merely individuals have perished, but whole genera and species; but of these the remains are still before us in the rocks; we can study their forms, and, from a comparison with recent species and genera, can arrive at some idea of their nature and functions. In this way, we are able to picture the various conditions of the earth when these organisms lived in succession upon its surface. Yet, we may readily conjecture, that in ancient eras many tribes and genera of plants and animals lived for ages, and then passed away without leaving any record of their existence. Many circumstances might concur to prevent the preservation of their remains. The species of the Hebrides were preserved in the usual manner, but the cemetery in which their remains were entombed has been washed away, and they can be seen nowhere else. It is as if on some isolated country there had lived a race of men, tall Patagonians, or swarthy Hottentots, or diminutive Laplanders, with a civilisation of their own; owing to some change of climate the race gradually dwindled down until it died out; eventually, too, the land settled down beneath the sea with all its ruined cities and villages, which, as they reached in succession the level of the waves, were torn up and dispersed, and other races at last voyaged over the site of that old land, dreaming not, that in bygone years fellow-mortals of an extinct type had pastured their herds where now there rolled a widespread sea.
[15] Quart. Jour. Geol. Soc., vol. xiv. p. 26.
But to return. We have seen that the long-continued action of the sea has been sufficient to breach and waste away the existing coast-line of western Scotland. When, therefore, such results are produced by so ordinary a cause, need we go to seek the agency of great debacles to explain the denudation of other parts of the country? It is known that at great depths currents have little effect upon the rocks which they traverse, and that their action is greater as it nears the surface. To account for the phenomena of crag and tail, and the general denudation of the country, we may suppose the land to have been often submerged and re-elevated. As hill after hill rose towards or sank below the sea-level, it would be assailed by a strong current that flowed from the west and north-west, until, in its slow upward or downward progress, it got beyond the reach of the denuding agencies. In this way the general contour of the land would be greatly though very gradually changed. Hills of sandstone, or other material of feeble resistance, would be swept away, the harder trap-rocks would stand up bared of the strata which once covered them, deep hollows would be excavated in front of all the more prominent eminences, and long declivities would be left behind them.—(See [Fig. 2].)
If my reader has ever visited the channel of a mountain-torrent—
"Imbres
Quern super notas aluere ripas"—
he must have noticed an exact counterpart to these appearances. When the waters have subsided, the overflowed parts are seen to be covered in many places with sand. Wherever a pebble occurs along the surface of this sand, it has invariably a hollow before it on the side facing the direction whence the stream is flowing, and a long tail of sand pointing down the channel. If we watch the motion of the water along its bed, the denuding agency may be seen actively at work. Every pebble that protrudes above the shallow streamlet arrests the course of the current, which is then diverted in three directions. One part turns off to the right hand of the pebble, and cuts away the sand from its flank; another part strikes off to the left, and removes the sand from that side; while a middle part descends in front of the pebble, and, by a kind of circular or gyratory movement, scoops out a hollow in the sand in front. Behind the pebble the water is pretty still, so that the sand remains undisturbed, and is further increased by the accumulation above it of sediment swept round by the lateral currents. Now, in place of the supposed stream, let us substitute the ocean with its westerly current—for the pebble, a great trap-hill—for the sand, easily friable shales and sandstones, and we have exactly the condition of things which produced crag and tail.
This process of destruction must have been in progress during many geological ages. We may suppose, that in that time the land often changed level, sometimes rising far above the sea, and sometimes sinking deep below it. We can well believe that the surface would often be covered with vegetation; that plants, widely differing from those which are now indigenous, clothed its hill-sides and shaded its valleys; and that animals of long extinct forms roamed over its plains or prowled amid its forests. When the country, in the lapse of centuries, sank beneath the sea-level, all trace of these scenes would eventually be effaced. The westerly currents would soon recommence the process of degradation, uprooting the forests, devastating the plains, wearing down the hills, and scooping out the valleys; and so, when the ocean-bed, in the course of ages, became again dry land, it would arise "another and yet the same." The little valley, where once, perchance, the mastodon used to rest his massive bulk amid a rich growth of ferns, shaded by the thick umbrage of coniferous trees, would emerge a deep glen with bare and barren rocks on either side; the site of the hill whereon herds of the gazelle-like anoplothere were wont to browse, might reappear a level plain; the low-browed rock, under whose shadow the ungraceful palæothere used of old to rest from the heat of the noon-tide sun, might emerge a beetling crag shooting up several hundred feet over the valley. It is by this repeated elevation and submergence, carried on for many ages, that our country has acquired its present configuration.
We can easily picture to ourselves the appearance which the British Islands would thus at different periods present. At one time, nearly the whole of England would be under water, with, however, a few islands representing the higher peaks of Cornwall; others scattered over the site of the West Riding of Yorkshire; and a hilly tract of land over what is now Wales. Scotland must have existed in a sorely mutilated state. A thick-set archipelago would represent the Cheviot Hills, and the country south of the Forth and the Clyde; north of which there would intervene a broad strait, with a comparatively large area of undulating land beyond, stretching across what is now the area of the Grampian Hills. A narrow fiord would run along the site of the Caledonian Canal, cutting the country into two parts, and running far into it on either side as deep lochs and bays. I have had such a condition of things vividly recalled when on the summit of a lofty hill in early morning, while the mists were still floating over the lower grounds, and only the higher hill-tops, like so many islands, rose above the sea of cloud. It was not a little interesting to cast the eye athwart this changing scene, and mark how each well-known peak and eminence looked when deprived of its broad sweep of base. What before had always seemed an abrupt precipitous summit, now took the form of a lonely rock or deep-sea stack, that might have served as a haunt for the gull and the gannet. The long swelling hill rose above the mist as a low undulating island, treeless and barren. It was easy to think of that wide expanse of mist as the veritable domain of ocean, to picture the time when these were veritable islands lashed by the surge, and to conjure up visions of ice-floes drifting through the narrows, or stranding on the rocks, amid a scene of wide-spread nakedness and desolation.
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 have likened 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 volume related 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 caves of 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. We know that there is a great difference between two millions and ten millions, but we cannot fully appreciate it, and so the periods 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 strange legends 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 had fallen 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.
The Flora, or vegetation of the Carboniferous era, differed widely 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 the Sphenopteris or 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 enjoyed the 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.
The Pecopteris ([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 the pteris, 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] The Neuropteris (as N. gigantea, [Fig. 6]) or nerve-leaved fern, is remarkable for its strongly-defined venation. It is scarcely, perhaps, so elegant in its outline as the sphenopteris, 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 our Osmunda regalis or royal fern. A species of the former class (N. cordata) might readily enough be mistaken for the young leaves of the Scolopendrium or 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 the Cyclopteris (C. dilatata, [Fig. 5]) or round-leaved fern, and the Odontopteris or tooth-fern. Most of these seem to have been lowly plants, like the ferns of our 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 long tapering 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 the alsophila of 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, the Cyathea, 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 the Caulopteris or 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 of Calamites. 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 called sternbergiæ, 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 called asterophyllites. 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 in [Fig. 9] is 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 as asterophyllites. 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-bearing asterophyllite. 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 evidently related 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 as lepidodendron ([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 call dichotomous,—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 the Lycopodiaceæ, 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 to have 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 hirsute cones called lepidostrobi ([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, called lepidophylla, 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 of stigmaria, 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 sometimes enough 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 the cacti and euphorbiæ, 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 of cyprides.
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 called sigillaria, 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 in which 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 marked by 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. 13 b], 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 the Geological 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 sculptured fleur-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. The incident 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. The fleur-de-lis recalled 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! The fleur-de-lis was 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 translated signet-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 form by reference to existing vegetation. Some of the species, as S. 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. (See [Fig. 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's Memoir, 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 branch measuring 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 imbedded in 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 to the 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.
[24] Witham's Foss. Veget. p. 31.
[25] For a more detailed description of the process, see Witham's Foss. Veget. p. 45.
[26] The solitary lignite of the Lower Old Red Sandstone, seems to have been araucarian. Miller's Footprints of the Creator, p. 203.
[27] Footprints of the Creator, p. 192.
These coniferous trees do not appear to occur among the erect stems of the coal-beds, at least they are very rare in such a position. Their more usual appearance is that of drifted, branchless trunks, imbedded along with other fragmentary plants in deep strata of sandstone. They probably grew on higher ground than the swamps which supported the sigillariæ and their allies, and might have been carried down by streams, freighted out to sea, and so deposited among the sediment that was gathering at the bottom.
The remains of cycadaceous plants have been described among the vegetation of the coal-measures; but only fragments have as yet been found. The modern Cycadeæ are low shrubs or trees, with thick stems of nearly uniform breadth, crowned with a dense clump of spreading fronds which resemble both those of the palms and the ferns. They are natives of the warmer regions of both hemispheres.
So long ago as the year 1835, Dr. Lindley figured a flower-like plant, to which he gave the name of Antholites, ranking it among the Bromeliaceæ, or pine-apple group. It was afterwards suspected by Dr. Hooker to belong rather to the coniferæ; and he supposed that the so-called flowerets might be really tufts of young unexpanded leaves. An examination of a more perfect specimen, however, has induced that distinguished botanist to alter his convictions and return to the original decision of Lindley, that the antholites are really flowers.[28] In [Fig. 15], therefore, which represents one of these coal-measure fossils, the reader beholds the oldest flower that has yet been found; and surely it is of no little interest to know, that amid the rank, steaming forests of the Carboniferous era, with all their darkness and gloom, there were at least some flowers—flowers, too, that were allied to still living forms, and breathed out a rich aromatic fragrance.
[28] See Dr. Hooker's remarks in the Supplement to the fifth edition of Lyell's Manual, p. 31.
Fig. 15.—Antholites.
In fine, from all the genera and species of plants that have been detected in the strata of the coal-measures, it would appear that the flora of that ancient period was in a high degree acrogenous—that is to say, consisted in great measure of ferns, club-mosses, and other members of the great group of plants known as acrogens. This word literally means top-growers, and is applied to those plants which increase in height, but not in width, since they attain at first nearly their ultimate diameter. Such plants occupy a low position in the botanical scale. Mingled with the numerous genera of carboniferous ferns and club-mosses, we find the remains of a much higher grade of vegetation—that of the gymnogens, or plants that bear naked seeds—such as the firs and pines. There also seem to have been a few endogenous flowering plants. Viewing, then, this flora on the whole, it presents us with many striking resemblances to certain botanical regions of the present day. Many of the tropical islands abound in ferns, and contain very few flowering plants. But New Zealand affords perhaps the closest parallel. That island is in certain parts highly mountainous, its loftiest summits being covered with glaciers. The hills throughout large districts are bare, or covered with a scanty herbage, while in other localities they are densely clothed with forests of pine, beech, and other trees. These forests sweep on to the lower grounds, where they are replaced by a thick growth of fern and flax-plant intermingled with dragon-trees and graceful tree-ferns, while the more swampy regions support a rich profusion of reeds and rushes. Such a condition of things affords a close parallel to the probable vegetation of the Carboniferous period—an immense preponderance of ferns and arborescent acrogens, with an intermixture of large coniferous trees. From the general scantiness of a flora where ferns predominate, it has been argued that the swamps of the coal-measures nourished a luxuriant repetition of comparatively few species; and this hypothesis also receives confirmation from the vegetation of New Zealand. Another deduction founded on the resemblance of the ancient to the modern flora, refers to the conditions of heat and moisture. It has been inferred that the climate of the coal period was equable and humid, like that of New Zealand—a supposition much more natural and simple than that, once so much in vogue, of a heated atmosphere densely charged with carbonic acid gas. That the air of the Carboniferous period differed in no material respect from the air of the present day, seems at last proved by the remains of air-breathing animals having been found among the coal-beds; and there seems no reason why the higher mountain-tops of the same epoch may not have been clothed with glaciers as those of New Zealand are. As yet we have no evidence of the fact, but it is by no means beyond the possibility of proof.[29]
[29] See Professor Ramsay's suggestive Memoir on Permian Breccias in Quarterly Journal of the Geological Society, vol. xi. p. 185.
CHAPTER V.
Scenery of the carboniferous forests—Contrast in the appearance of coal districts at the present day—Abundance of animal life in the Carboniferous era—Advantages of palæontology over fossil-botany—Carboniferous fauna—Actiniæ—Cup-corals—Architecture of the present day might be improved by study of the architecture of the Carboniferous period—Mode of propagation of corals—A forenoon on the beach—Various stages in the decomposition of shells—Sea-mat—Bryozoa—Fenestella—Retepora—Stone-lilies—Popular superstitions—Structure of the stone-lilies—Aspect of the sea-bottom on which the stone-lilies flourished—Sea-urchins—Crustacea, their high antiquity—Cyprides—Architecture of the Crustacea and mollusca contrasted—King-crabs.
The forms of vegetation that flourished during the Carboniferous era seem to have been in large measure marshy plants, luxuriating on low muddy delta-lands, like the cypress-swamps of the Mississippi, or the Sunderbunds of the Ganges. We can picture but faintly the general scenery of these old forests from the broken and carbonized remains that have come down to us. But though perhaps somewhat monotonous on the whole, it must have been eminently beautiful in detail. The sigillariæ raised their sculptured stems and lofty waving wreaths of fronds high over the more swampy grounds, while a thick underwood of ferns and star-leaved asterophyllites clustered amid the shade below. The lepidodendra shot forth their spiky branches from the margin of green islets, and dropped their catkins into the sluggish water that stole on among the dimpled shadows underneath. Tree-ferns spread out their broad pendant fronds, and wrapt the ground below in an almost twilight gloom, darker and deeper far than that
"Hospitable roof
Of branching elms star-proof,"
which rose so often in the visions of Milton; or that "graceful arch" so exquisitely sung by Cowper, beneath which
"The chequered earth seems restless as a flood
Brushed by the wind. So sportive is the light
Shot; through the boughs, it dances as they dance,
Shadow and sunshine intermingling quick,
And darkening and enlightening, as the leaves
Play wanton, every moment, every spot."
Thickets of tall reeds rose out of the water, with stems massive as those of our forest-trees, encircled at regular distances by wreaths of pointed leaflets, and bearing on their summits club-like catkins. Far away, the distant hills lay shaggy with pine-woods, and nursed in their solitudes the springs and rivulets that worked a devious course through forest, and glen, and valley, until, united into one broad river, they crept through the rich foliage of the delta and finally passed away out to sea, bearing with them a varied burden of drift-wood, pine-trees from the hills, and stray leaves and cones from the lower grounds.
How different such a scene from that now presented by the very same areas of country! These old delta lands are now our coal-fields, and have exchanged the deep stillness of primeval nature for the din and turmoil of modern mining districts. In these ancient times, not only was man uncreated, but the earth as yet lacked all the higher types of vertebrated being. None of the animals that we see around us existed then; there were no sheep, nor oxen, horses, deer, nor dogs. Neither were the quadrupeds of other lands represented; the forests nourished no lions or tigers, no wolves or bears, no opossums or kangaroos. In truth, the land must have been a very silent one, for we know as yet of no animated existence that could break the stillness, save perchance some chirping grasshopper, or droning beetle, or quivering dragon-fly. No bee hummed along on errands of industry; it is doubtful, indeed, whether honey-yielding flowers formed part of the carboniferous flora; no lark carolled blithely in the sky, nor rook croaked among the woods. All was still; and one might, perhaps, have stood on some of those tree-crested islets, and heard no sound but the rippling of the water along the reedy and sedgy banks, and the rustling of the gloomy branches overhead.
To one who muses on these bygone ages it is no unimpressive situation to stand in the midst of a large coal district and mark its smoking chimneys, clanking engines, and screaming locomotives, its squalid villages and still more squalid inhabitants, and its mingled air of commercial activity, physical wretchedness, and moral degradation. It is from such a point of view that we receive the most forcible illustration of those great changes whereof every country has been the scene, and which are so tersely expressed by one who has gazed on the revelations of geology with the eye of a true poet—
"There rolls the deep where grew the tree.
O earth, what changes hast thou seen!
There where the long street roars, bath been
The stillness of the central sea."
But the lifelessness of the carboniferous forests was amply compensated by the activity that reigned in river, lagoon, and sea. Coral groves gleamed white beneath the waves, fishes of many a shape disported in stream and lake, and the bulkier forms, armed in massive plates of bone, ascended the rivers or haunted the deeper recesses of the open sea. In some beds of rock the remains of these various animals lie crowded together like drifted tangle on the sea-shore, and the whole reminds us of a vast cemetery or charnel-house. The bones lie at all angles, many of them broken and disjointed as though the owner had died at a distance, and his remains, sadly mutilated on the way, had been borne to their last resting-place by the shifting currents; others lie all in place, covered with their armature of scales, as though the creature, conscious of approaching dissolution, had sought out a sheltered nook and there lain down and died. It is not uninteresting or uninstructive to tract; out in an old quarry stratum above stratum, each with its groups of once living things. I know of few employments more pleasant than to sit there, amid the calm stillness of a summer evening, when the shadows are beginning to steal along the valleys and creep up the hill-sides, and in that dim fading light to try in fancy to clothe these dry bones with life, to picture the time when they lived and moved in the glassy depths of lakes and seas, or amid the solitudes of jungles and forests, and so to spend a pleasant hour in reverie, till roused at last by the vesper song of the lark, or the low meanings of the night wind as it sighs mournfully through the woods.
The study of fossil animals embraces a much greater range of subject than that of fossil plants. The fauna of any particular geological formation, that is to say, its embedded animal remains, for the most part vastly exceeds in number its flora, or vegetable remains, and is likewise usually better preserved. About the nature and affinities of several tribes of fossil plants there hangs an amount of uncertainty which renders them a dubious guide to the climatal and other conditions of the period and locality in which they lived. Generic distinctions among living plants often rest on the character of those parts which are the most perishable, such as flowers and seed-vessels. These delicate structures we, of course, can hardly look to find preserved in the rocks, and we have in place of them only detached leaflets, twigs, branches, and stems, often sorely mutilated in outward form, and presenting no trace of internal organization. But the tribes of the animal kingdom have, for the most part, harder frameworks. The minute infusoria, which by their accumulated remains help to choke up the delta of the Nile, and swarm by millions in every ocean of the globe, have their silicious or calcareous shells so minute that Ehrenberg has estimated a cubic inch of tripoli to contain forty-one thousand millions of them. The polypi have their internal calcareous skeletons, which abound in all the older limestones, and form the coral reefs of the present day. The mollusca, too, though, as their name imports, they have perishable bodies, are yet, in most cases, furnished with hard calcareous shells, that indicate by their various modifications of form and structure, the character of the animal that lived within them. They are found in all the formations from the earliest upwards, and as they vastly exceed in numbers all the other classes with which the geologist has to deal, they form the larger part of that basis of evidence from which he interprets the past history of organized existence. Hugh Miller loved to talk of them as the "shell alphabet," out of which the language of palæontological history should be compiled. The vertebrata, too, all have their hard skeletons, easily capable of preservation, whether it be in the form of the massive exo-skeleton of bone that characterized the older ganoidal fishes, or the compact endo-skeleton of the reptiles and mammals. A greater amount of attention is, therefore, due to the study of fossil animals, since they thus not only far exceed fossil plants in number, but possess a higher value as evidence of ancient physical conditions.
The fauna of the Carboniferous system is a very numerous one, exhibiting specimens of almost every class of animal life, from the tiny foraminifer up to the massive bone-covered sauroidal fish, and even to occasional traces of true reptilian remains. By far the larger number are peculiar to the sea, such as the molluscan tribes and corals; others are undoubtedly terrestrial organisms, such as the wings and wing-sheaths of several kinds of insects; while some appear to be peculiar to fresh or brackish water, such as shells allied to our unio or river-mussel, and minute crustaceous animals known as cyprides, of which we have still representatives in our ponds and ditches. It is plain, then, that if we rightly ascertain the class or family to which one of these fossils belonged, we shall obtain a clue to the history of the physical geography, during Carboniferous times, of the district in which the fossil occurs. A bed of unios will tell us of old rivers and lakes that spread out their blue waters where now, perchance, there lie waving fields of corn. A bed of corals and stone-lilies will lay before us the bottom of an ancient ocean that rolled its restless waves where to-day, perhaps, the quarryman plies his task amid the gloom of dark pine-woods. In short, these organic remains are to the history of the earth what ancient monuments are to the history of man. They enable us to trace out the varied changes of our planet and its inhabitants down to the human era, just as the wooden canoe, the flint arrow-head, the stone coffin, the bronze sword, the iron cuirass, the ruined abbey, and the feudal castle, teach us the successive stages of progress in the history of our own country.
Whoever has spent a few days on some rocky coast, must have noticed adhering to half-tide stones numerous solitary actiniæ. Arrayed in all the colours of the rainbow—purple, green, and gold—these little creatures hang out their tentacles like so many flowers, and have hence received the popular name of sea-anemones. Their internal structure is no less beautiful. They resemble so many large plump gooseberries, and consist of a little sack suspended within a larger one. The outer sack is fringed along its upper edges with one or more rows of slim hollow tentacles, which diverge outwards like the petals of the daisy, and can be contracted at pleasure so as somewhat to resemble the daisy when folded up at sunset. The inner sack, which forms the stomach of the animal, has a short opening or gullet, at the upper part of which is the mouth lying in the centre of the cavity surrounded by the fringes of tentacles. The inner sack is connected with the outer by means of thin membranes, like so many partition-walls, which radiate inwards like spokes towards the axle of a wheel. The space between each of these membranes, or lamellæ, forms an independent chamber, but it has a communication with those on either side by a window in each wall, and further opens upwards into the hollow tentacles, which, with minute orifices at their outer points, may be compared to chimneys. These chambers form the breathing apparatus of the little creature. Sea-water passes down through the tentacle into the hollow chamber below, whence, by the constant action of minute hairlike cilia that line the walls like tapestry, it is driven through the window into the next chamber, thence into the next, and so on, passing gradually through the tentacles back to the sea.
The actiniæ are of a soft perishable substance, but many of the other Anthozoa, or flower-like animals, have hard calcareous skeletons. Of such a kind are the polypi that in the Pacific Ocean have raised those stupendous reefs and islands of coral. It does not appear that, during the Carboniferous period, there existed any reef-building zoophytes, but some of the most abundant forms of life belonged to a kindred tribe, and are known by the name of Cyathophyllidæ, or cup-corals.
As the name imports, the typical genus has a general cup-shaped form, but this is liable to many aberrations in the cognate genera. The younger specimens of one species (Cyathopsis fungites) have a curved outline somewhat like the bowl of a tobacco-pipe, whence the quarrymen know them as pipe-heads. The older individuals are generally more or less wrinkled and twisted, sometimes reaching a length of eight or nine inches, and have been named by the workmen rams'-horns.
Fig. 16.—Cyathopsis (clisiophyllum ?) fungites.
The annexed figure ([Fig. 16]) shows their general appearance and structure. The lower end was fixed to the rock like the flat sucker-like disc of the actinia. Around the outer margin there diverged one or more rows of slim tentacles, hollow, soft, and retractile, like those of the actinia. From the margin to the centre there radiated more than a hundred lamellæ, but these differed from the corresponding membranes of the modern animal, inasmuch as they were strengthened internally by a skeleton of hard carbonate of lime; and to this difference we owe their preservation. They stand out in high relief upon weathered specimens, showing the long, narrow chambers that ran between them. Their walls were once doubtless hung with countless vibratile cilia, and perhaps pierced each with its window, through which the currents of water passed in their ceaseless progress to and from the sea. At the centre lay the mouth, communicating by a short gullet with the stomach, which occupied the central portion of the animal, and from the outer walls of which the lamellæ diverged like so many buttresses. In its youngest stages, the animal occupied the whole length of the cup, but, us it increased in size, it gradually retreated from the narrow end, which was then divided off by a thin calcareous membrane. At each successive stage of its growth, a new membrane was added, each further and further from the lower end, so that eventually the creature left below it a series of empty chambers all firmly built up. Thus, in a specimen six or eight inches long, there would in reality only be a small part tenanted—in fact merely the upper floor—all the lower storeys remaining silent and uninhabited. The house of this old-world architect differed widely in one respect from human dwellings. Man begins his basement story of the same dimensions as those that are to succeed it, or, if any difference is made at all, the upper floors are built each less than the one below it, so that the whole structure tapers upward to a point, as in the Pyramids. But the cyathopsis reversed this latter process; it inverted the cone, commencing the smallest chamber at the bottom, and placing the widest at the top. Indeed, one is sometimes puzzled to conjecture how so bulky a building could be securely poised on so narrow a basis, and it is certainly difficult to see how the creature could move about with such a ponderous load to drag along. The snail carries his house on his back, yet it is a slim structure at the best; but the cup-coral must not merely have carried his house, but some dozen or two of old ones strung one after another to his tail. Perhaps, though free to move about and try change of residence in its youthful days, the creature gradually settled down in life, and took up its permanent abode in some favourite retreat, the more especially as in process of time it became what we should call a very respectable householder.
Allied to the cyathopsis is another and still more beautiful coral, described so long ago as the latter part of the seventeenth century by the Welsh antiquary and naturalist, Lhwyd, under the name of Lithostrotion. Although many perfect specimens of it have been found, and it is usually as well preserved as any of its congeners, men of science have been sadly at a loss what to call it. Four or five synonyms may be found applied to it in different works on palæontology. There seems now, however, a tendency to return to the name that old Lhwyd gave it two centuries ago; the family to which it belongs, and of which it is the type, has accordingly been termed the Lithostrotionidæ, and the species in question Lithostrotion striatum ([Fig. 17]). It differed from the cyathopsis in several respects, but chiefly in this, that it lived in little congregated groups or colonies, whereas the cyathopsis, like our own actinia, dwelt alone.
Fig. 17.—Lithostrotion striatum.
Each of these colonies was formed of a cluster of hexagonal, or rather polygonal pillars, fitting closely into each other, like the basaltic columns of Fingal's Cave, and springing from a common base at the sea bottom.[30] Each pillar constituted the abode of a single animal, and resembled generally the stalk of the cyathopsis. It had the same minute diverging partitions running from the outer walls towards the centre, and the same thin diaphragms, which, stretching horizontally across the interior of the column at short intervals, marked the successive stages of the animal's growth. Within these partitions, which vary from forty to eighty in number, there runs an inner circular tube with thin lamellæ and diaphragms. The exterior of the columns is ribbed longitudinally by a set of long fine striæ, which give somewhat the appearance of the fluting on a Corinthian pillar. The columns, moreover, are not straight, but have an irregular, wrinkled outline, so that, by a slant light, they look like some old pillar formed of many layers of stone, the joints of which have wasted away, producing an undulating profile in place of the original even one. But in these ancient coral columns there is no blunted outline, no worn hollow; the sculpturing stands out as sharp and fresh, and the wavy curves as clearly defined, as though the creature had died but yesterday. They resemble no order of human architecture, save faintly, perhaps, some of the wavy outlines of the Arabesque.
[30] Sir Roderick Murchison figures in his Siluria, p. 282, a gigantic specimen, which measured two feet four inches in width.
Despite all the improvements and inventions of modern times, classic architecture has made no progress since the days of Pericles. All that we do now is but to reproduce what the Greeks created 2000 years ago, and he is reckoned the best architect who furnishes the best imitation. Our architects might find some useful hints, however, by studying the lowlier orders of nature. They would see there patterns of beauty far more delicate than the Grecian capital, and more light and airy than the Gothic shaft. And whether or not they could found a new order of architecture, they could not fail to discover many modifications and improvements upon some of the old. They could not readily light upon a more graceful form than that of the lithostrotion, would they but picture it as it grew at the bottom of the old carboniferous sea. A group of hexagonal pillars, firmly compacted together like those of the Giant's Causeway, or Fingal's Cave, rose from a white calcareous pediment, as columns from the marble steps of an Athenian temple. Each side of the pillar had a wavy undulating surface, delicately fluted by long slender striæ, the whole being so arranged that the convexities of one surface fitted into the sinuosities of the adhering one. Each pillar was crowned above by a capital, consisting of the soft vibratile tentacles of the animal, that hung over like so many acanthus leaves. Of the form of these tentacles, their design and grouping, we know nothing save what may be gathered from the analogy of living corals. There can be little doubt, however, that, like the flower-shaped buds of the existing reef-building polyps, they must have been eminently beautiful, and in strict keeping with the graceful column which they crowned.
Another kindred form was that known as the lithodendron. It, too, grew in colonies, and seems to have closely resembled the last, save that the pillars, in place of being six-sided, were round. I have seen a bed of these corals several yards in extent, and seven or eight inches deep, where the individuals were closely crowded together, so as to resemble a series of tobacco-pipe stems, or slim pencils set on end. The tubes, however, were not all quite straight; many being more or less curved, and sometimes crossing their neighbours obliquely. The internal arrangement was on the same plan as in the two previous corals. The same numerous partitions ran from the exterior wall towards the central tube, the same thick-set diaphragms crossed the entire breadth of the column, imparting the same minute honey-combed appearance to a cross section. The exterior of the column (in L. fasciculatum) was likewise traversed by the same longitudinal striæ.
Both these corals seem to have been fissiparous, that is to say, they propagated by splitting into two parts, each of which formed the base of a new column with a new animal. The evidence for this statement rests on the fact, that many of the tubes are seen to bifurcate in their course, so that two new tubes are produced equal in size and completeness to the old one from which they proceed. Another mode of generation which, in at least its earlier stages, would produce a somewhat similar appearance is called gemmation, and consists in the protrusion of a bud or gemmule from the side of the animal, which shortly develops into a new and perfect individual. It is probable, however, that the ordinary mode of propagation among these old corals was the usual one by impregnated ova. These ova, like those of our sea-anemones, were probably generated within the partitions, between the central stomach and the outer wall, whence they passed down into the stomach, and were ejected by the mouth of the parent as little gemmules, furnished with the power of locomotion by means of vibratile cilia. Some of the Medusa family possess this three-fold mode of propagation; but, in all, the last-mentioned is the most usual.
Has the reader ever stretched himself along the shore, while, perhaps, a July sun blazed overhead, and a fitful breeze came over the sea, just strong enough to chase ashore an endless series of rippling wavelets, and breathe over his temples a delicious and refreshing coolness? Thus placed, and gazing dreamily now, perchance, at the distant sails like white specks along the boundary line of sea and sky; now at the gulls wheeling in broad circles through the air, and shooting swift as arrows down into the blue water, he must often have turned to look for a little at the sand which, heaped up in little mounds around him, formed a couch well-nigh as soft as the finest down. Many a varied fragment entered into the composition of that sand. Mingled among the minuter quartzy particles lay scores of shells, some with the colour not yet faded, and the valves still together—the delicate tellina, with its polished surface, and its flush of pink; the cardium with its strong white plaited sides, and the turritella with its circling spire; some were worn down and sorely effaced, others broken into fragments by the ceaseless grinding of the waves. It was pleasant labour in such a sultry noon to pick out the shells of one species in all stages of decay. The Trochus lineatus, or Silver Willie, as young ramblers by the sea-shore love to call it, showed well the process of destruction. The perfect shell, cast ashore, perhaps, by the last storm, and still uninjured by the tides, displayed its russet epidermis, or outer skin, covered with fine brown zig-zag lines, running across the whorls from the creature's wide pearl-lined mouth to the apex. A second shell exhibited a surface that had begun to suffer; the point had been divested of its thin outer skin, and laid bare the silvery coating of pearl below. A third had undergone a still longer period of abrasion, for the whole of the epidermis was gone, and the surface gleamed with a pearly iridescence. In yet a fourth, this bright exterior had been in large measure worn away, and the blunted, rounded shell displayed the dull white calcareous substance of which it was mainly built up. But there were other objects of interest in the sand: bits of tangle, crusted over with a fine net-work of gauze, and fragments of thin leaf-like membrane, consisting of a similar slender network known popularly as the sea-mat, occasionally turned up among the pebbles and shells. No one who met with these organisms for the first time could fail to be struck with the extreme delicacy of finish, if one may so speak, that characterizes them. And yet he might be puzzled to know what to make of them. The leaf-like membrane, at a first glance, looks not unlike some of the flat-leaved algæ, and such the observer might readily take them to be. Such, too, they were long regarded by naturalists; but a more careful examination of them showed that the so-called plants really belonged to the animal kingdom, and that the supposed leaves were, in truth, the organic dwelling-places of minute zoophytes, of which many hundreds lay grouped together on every square inch. For many years these little creatures were called "celliferous corallines," and classed among the polypi, that great tribe which has its representatives in every ocean, from the coral reefs of the Pacific to the little bell-shaped hydra amid the tangle of our own seas. But the microscope—that lamp which lights us into the inner recesses of nature—revealed at last their true character. Fixed to one spot, living in communities, and exceedingly minute, in short, with many of the outward features of the true corallines, they were yet found to possess a structure so complex and highly organized, as to entitle them to rank among the higher tribes of the invertebrate animals, and they are now accordingly pretty generally subjoined to the mollusca, under the name of Bryozoa.
Each bryozoon consists externally of a single horny or calcareous cell, sometimes furnished with a valve-like lid that folds down when the animal withdraws itself. When danger is past, and the creature begins again to emerge, the upper parts, which were drawn in like the inverted finger of a glove, are pushed out until a series of tentacles, covered with minute hair-like bodies, called cilia, are expanded. The vibratile motion of these cilia causes a constant current in the direction of the mouth, which lies in the centre of the hollow whence the tentacles spring; animalcules are in this way brought in rapid succession within reach of the mouth, and form a never-failing source of nourishment. The interior is greatly more complex than that of the polypi. The stomach is connected above with a cavity like the gizzard of a bird, furnished with pointed sides, which serve to triturate the food before it passes into the stomach. There is also a distinct intestine. The muscular action for the expansion and retraction of the animal is highly developed, and the generative system is a greatly more complex one than that of the polyps already referred to. In short, however closely they might be thought to resemble the corals in outward form, their internal structure undoubtedly links them with a much higher type of organization, and justifies the naturalist in subjoining them as a sub-order to the mollusca.
The cells are grouped at short intervals along a horny or calcareous substance, that sometimes encrusts sea-weed, or spreads out as a flat leaf-like membrane, or rises into cup-shaped or dendritic forms. A series of cells constituting a separate and independent colony, is termed a polypidom. The cells are further connected together by an external jelly-like integument, in which they are sunk, and which serves to secrete the calcareous particles from the sea.
It is interesting to know that creatures so minute and yet so complexly organized, existed abundantly in the seas of the Carboniferous period. No less than fifty-four species are enumerated as having been obtained from the carboniferous strata of the British Islands, and scarcely a year passes without one or two new species being added to the list. The most frequent belong to the genus Fenestella, or little window, a name indicative of the reticulated grouping of the branches like the wooden framework of a window. Each of these branches, or interstices, as they are called, was more or less straight, being connected with that on either side by a row of transverse bars, just as the central mullion of an abbey window is connected with the flanking ones by means of cross-bars of stone. Not unfrequently some of the branches subdivide into two, as we saw to be the case among the cup-corals.
Fig. 18.—a, Fenestella oculata (M'Coy), nat. size; b, magnified portion of the same.
[Fig. 18] illustrates the relative disposition of these branches. In a, the natural size of the fossil is given; b is a portion of the same magnified, to show the form and arrangement of the ribs and cross-bars. Each rib is seen to have two sides separated by a rounded ridge. Along each side there runs a row of circular hollows or cells, every one of which once formed the abode of a distinct bryozoon. The back or inner surface of the branch, was ribbed and granulated irregularly, without any cells. The connecting bars or dissepiments have no cells, and served merely to bind the interstices together into one firm organically-united polypidom. Such fragments as that here figured are the most usual traces to be found of these animals among the carboniferous rocks. But perfect specimens are sometimes met with which show how delicate and graceful a structure the polypidom of some of the fenestellæ must have been. All these bars sprung from a common point as their basis, and rose up in the form of a cup. It was, in short, a cup of network, hung with waving tentacles and quivering cilia. I have seen some dissections of flowers in which all the softer tissue had been removed, so as to present only the harder veinings of the leaves with their thousand ramifications bleached to a delicate whiteness. Out of these skeleton-leaves there were formed groups of lilies, crocuses, geraniums, and roses, like patterns of the finest gauze. Some of the larger-stemmed leaves that had been artistically moulded into a tulip form, seemed not inaptly to represent the general contour of the skeleton of the old carboniferous fenestella.
An allied form is called the Retepora. It differed from the previous organism in having the ribs not straight, but irregularly anastomosing, that is, running into and coalescing with each other, so as to form a close network with oval interspaces, like a piece of very minute wire-fence. Each of these wavy libs was completely covered over on one side with oval pores or cells, which, as in the fenestella, formed the abode of the living animals. The differences in organization between the animal of fenestella and that of retepora can, of course, only be matter of speculation. The general structure in both must, however, have been pretty much alike. The former genus is now no longer extant, but the latter, which was ushered into the world during the era of the Old Red Sandstone, still lives in the deeper recesses of the ocean, and manifests in its structure and habits the leading characteristics of bryozoan life.
What rambler among old lime-quarries is not familiar with the stone-lily, so abundant an organism in most of the Palæozoic and many of the Secondary limestones? In some beds of the carboniferous limestone its abundance is almost incredible. I have seen a weathered cliff in which its remains stood out in bold relief, crowded together, to use an expression of Dr. Buckland's, "as thickly as straws in a corn-rick." The joints of this animal, known now as entrochi or wheel-stones, forced themselves on the notice of men during even the middle ages, and an explanation was soon found for their existence. From their occurring largely about the coast at Holy Island, they were set down as the workmanship of Saint Cuthbert.
"On a rock by Lindisfarne,
St. Cuthbert sits and toils to frame
The sea-born beads which bear his name."
The aged saint was represented as employing his nights in this highly intellectual task, sitting on a lone rock out in the sea, and using an adjacent one as his anvil.
"Such tales had Whitby's fishers told,
And said they might his shape behold,
And hear his anvil sound,
A deaden'd clang,—a huge dim form
Seen but, and heard, when gathering storm
And night were closing round."
But these wheel-stones were not the only geological curiosities to which this simple mode of explanation was applied. In the same storied neighbourhood there occur in considerable numbers the round whorled shells of the genus Ammonites. These were gravely set down as petrified snakes wanting the head, and their petrifaction and decapitation were alike reverently ascribed to the power of the sainted abbess of Whitby.
"They told
How of a thousand snakes each one
Was changed into a coil of stone
When holy Hilda prayed."
The stone-lily belonged to that large class of animals ranked together as Echinodermata, a name taken from one of the leading subdivisions of the group—the Echini or sea-urchins. It seems to have been one of the earliest forms of life upon our planet, its disjointed stalks occurring largely in some of the oldest Silurian limestones. In the Secondary ages it began gradually to wane, until at the present day its numerous genera appear to be represented by but the comatula and the pentacrinite, two tiny forms that float their jointed arms in the profounder depths of the sea.
Fig. 19.—a, Cyathocrinites planus. b, Encrinal stem, with uniform joints. c, Single joint, or wheelstone.
As its name imports, the stone-lily or encrinite had a plant-like form. It consisted of a long stalk fixed by the lower end to the sea-bottom, and supporting above a lily-shaped cup, in which were placed the mouth and stomach ([Fig. 19 a]). The stalk consisted of circular plates (some of them not so thick as a sixpence), having their flat sides covered with a set of minute ribs radiating from the centre, and so arranged that the prominent lines of one joint fitted into corresponding depressed lines of the adhering ones. The centre of each joint was pierced by a small aperture, like the axle of a wheel, which, when the stem was entire, formed part of the long tube or canal that traversed the centre of the stem, and served to convey aliment to the remotest part of the animal. Detached joints have thus a wheel-like appearance (Fig 19 c), and hence their common name of wheel-stones. In many species they were not all of the same diameter, but alternately larger and smaller, as if the stem had been made up of a tall pile of sixpences and threepenny pieces in alternate succession. This variation gives a remarkably elegant contour to the stalk. The flower-shaped cup consisted of a cavity formed of geometric calcareous plates, and fringed along its upper margin with thick calcareous arms, five or ten in number, that subdivided into still more slender branches, which were fringed along their inner side with minute cirri or feelers. All these subdivisions, however fine, were made up of calcareous joints like the stalk, so that every stone-lily consisted of many thousand pieces, each perfect in its organization and delicate in its sculpturing. One species peculiar to the Liassic formation (Extracrinus Briareus) has been calculated to contain one hundred and fifty thousand joints!
The effect of this minute subdivision was to impart the most perfect flexibility to even the smallest pinnule. The flower could instantly collapse, and thus the animals on which the encrinite preyed were seized and hurried to the central mouth. The lower part of the cup, or pelvis, as it is called, contained the stomach and other viscera, and communicated with the most distant part of the body by the central alimentary canal.
But while this continued the general type on which the encrinites were constructed, it received many minor modifications. These were effected chiefly on the form and arrangement of the cup-shaped body and its appendages, and form now the basis of our classification into genera and species. Thus, in the genus known as Platycrinus, the lower part of the cup consists of two rows of large hexagonal or polygonal plates fitting closely into each other, while the upper part rises into a dome-like elevation formed of smaller polygonal plates, which have often a mammillated exterior. The arms sprang from the widest part of the body where the large pieces of the lower cup were succeeded by the small pieces of the upper. In an Irish species (P. triacontadactylus), the arms subdivided into thirty branches, each fringed with minuter pinnules and folding round the central elevated spire, as the petals of a crocus close round its central pistil. In another encrinite (Poteriocrinites conicus), the cup was shaped like an inverted cone, the point being affixed to the summit of the stalk, and the broad part throwing out from its edges the lateral arms. The Woodocrinus macrodactylus had such gigantic arms as well-nigh to conceal the position of the cup, which relatively was very small in size. They sprang from near the base of the cup, five in number, but soon subdivided each into two, the ten arms thus produced being closely fringed with the usual jointed calcareous pinnules.
The size and arrangement of the joints of the stalk also differed in different genera. The Woodocrinus and many others had them alternately broad and narrow, like a string of buttons of unequal sizes; others had all the joints of the same relative diameter ([Fig. 19 b]), so that the stalk tapered by a uniform line from base to point. I may add, that on some specimens of both these kinds of stems, we can notice small, solitary areolæ, or scars, which may mark the points of attachment of cirri, or little tentacles, like those on the stem of the existing Pentacrinite. But though each of these varieties of stem is peculiar to a certain number of genera, there is often so little distinction among the detached fragments, that it becomes difficult, indeed impossible, to assign each to its appropriate individual. We may say, that certain encrinal stalks could not have belonged to a poteriocrinus, and others could never have fitted on to the cup of an actinocrinus; but we cannot often say positively to what species they actually would have fitted. There can, however, be no doubt about their being encrinites, and so we have in them a safe and evident test for the origin of the rock in which their remains occur. But to this I shall afterwards revert.
In the meantime, I would have the reader to fix the stone-lily in his memory as peculiarly and emphatically a marine animal, dwelling probably in the deeper and stiller recesses of the ocean, like the Pentacrinite of existing times. Let him try to remember it, not in the broken and sorely mutilated state in which we find it among the blocks of our lime-quarries, but as it must have lived at the bottom of the carboniferous seas. The oozy floor of these old waters lay thickly covered with many a graceful production of the deep, submarine gardens of
"Violet, asphodel, ivy, and vine-leaves, roses and lilies,
Coral and sea-fan, and tangle, the blooms and the palms of the ocean."
Amid this rich assemblage of animated forms, the stone-lilies must have occupied a conspicuous place. Grouped in thick-set though diminutive forests, these little creatures raised their waving stems, and spread out their tremulous arms, like beds of tulips swaying in the evening air. Their flower like cups, so delicately fringed, must have presented a scene of ceaseless activity as they opened and closed, coiling up while the animal seized its prey, or on the approach of danger, and relaxing again when the food had been secured, or when the symptoms of a coming enemy had passed away. Only from this animated action would one have been apt to conjecture these organisms to be other than vegetable. They lived, too, not in detached patches, like the tulip-beds of the florist, but, to judge from the abundance of their remains, must have covered acre after acre, and square mile 'after square mile, with a dense growth of living, quivering flowers. As one individual died out, another took its place, the decaying steins and flowers meanwhile falling to pieces among the limy sediment that lay thickly athwart the sea-bottom, and contributing, by their decay and entombment, to build up those enormous masses of rock, known as the mountain-limestone, which stretch through Yorkshire and the central counties into Wales.