Our survey has hitherto been directed to the denizens of carboniferous lake, river, and sea, and we have found them to be alike important in numbers and interesting in organization. It is otherwise, however, when we turn in search of the denizens of the carboniferous lands. The crowded trees and shrubs of the coal strata recalling as they do old forest-covered swamps, might seem to indicate the probability of a pretty numerous terrestrial fauna. Where are we to look for the fossilized relics of land animals, if not in the remains of a submerged land-surface? And yet, strange as it may seem, of the inhabitants of the land during the Coal-measure period we know almost nothing. "We have ransacked hundreds of soils replete with the fossil roots of trees,—have dug out hundreds of erect trunks and stumps, which stood in the position in which they grew,—have broken up myriads of cubic feet of fuel, still retaining its vegetable structure,—and, after all, we continue almost as much in the dark regarding the invertebrate air-breathers of this epoch, as if the coal had been thrown down in mid-ocean."[50]
[50] Sir Charles Lyell's Elements, fifth edition, p. 406.
The little land-shell already noticed as having been detected by Sir Charles Lyell in the carboniferous rocks of Nova Scotia, seems to be as yet the only air-breathing mollusc obtained from rocks of such high antiquity. Insect remains have been detected in the English coal-fields belonging to two or three species of beetles; while on the Continent, wing-sheaths and other fragments of cockroaches, scorpions, grasshoppers, locusts, crickets, &c., have been detected. But the most remarkable traces of air-breathers consist in various indications of the existence of reptiles during the Carboniferous era. Fragmentary skeletons, with detached bones and plates, have been found in Bavaria and America, together with long tracks of footprints, from which it appears that during the time our coal-seams were forming, there swam through the sluggish deltas, or crept amid the dank luxuriant foliage, strange lizard-like forms, large enough to leave behind them on the soft yielding mud or sand the impress of their double pair of toed feet. But of these animals we have much to learn. Some of them have bequeathed to us merely their dismembered broken bones; others have left but the imprints of their toes. Yet even these remains, trifling as they may seem, become of importance when we remember that they demonstrate fishes not to have been the highest types of being during the epoch of the Coal, and show that while the bulky holoptychius held the supremacy of the waters, lizard-like forms of a less formidable type seem, so far as we know, to have ruled it over the land.
In fine, then, no one can glance at a list of the carboniferous fauna without perceiving either that the animated world of that ancient epoch must have had a very different proportioning from what now obtains, or that we have only a meagre and fragmentary record of it. That the latter conclusion is the more philosophical will appear if we reflect upon the many chances that exist against the entombment and preservation of animal remains, especially of those peculiar to the land. How very small a proportion of the remains of animals living in our own country could be gathered from the surface-soil of any given locality, and how very inadequate would be the meagre list of species thus obtained, as representing the varied and extensive fauna of Great Britain! In contrasting, then, the rich abundance of marine organisms with the extreme paucity of terrestrial animals among the carboniferous rocks, it would be too hasty to infer a corresponding disproportion originally. It must be admitted that the rarity of air-breathers, after such long-continued and extensive explorations among terrestrial and lacustrine beds, presents a difficult problem, only (if at all) to be cleared away by patient and persevering investigation. With this preliminary caution, we may regard the carboniferous fauna as peculiarly rich in marine species. The sea-bottoms swarmed with stone-lilies, cup-corals, and net-like bryozoa, mingled with the various tribes of molluscan life—the brachiopods with their long ciliated arms; the bivalves and gastropods with their coloured shells that recall some of the most familiar objects of our shores; and the cephalopods with their groups of siphonated chambers, straight as in the orthoceras, or gracefully coiled as in the goniatite. The seas swarmed, too, with fishes belonging to the two great orders of ganoids and placoids, the latter represented now by our sharks and rays, though the exact type of the ancient genera is retained only by the cestracion or Port-Jackson shark; the ganoids, with their strong armour of bone, represented by but two genera, the lepidosteus of the American rivers, and the polypterus of the Nile,—two fishes that seem but as dwarfs when placed side by side with the gigantic holoptychius of the coal-measures. The rivers and estuaries of the same period seem to have been frequented by immense shoals of the smaller ganoidal fishes that fed on decaying matter brought down from the land, and perhaps, too, on the minute Crustacea that lay strewed by myriads along the bottom. Into these busy scenes the bulkier monsters from the sea made frequent migrations, perhaps in some cases ascending the rivers for leagues to spawn, and returning again to their places at the mouth of the estuary or in open sea. The rivers and lakes swarmed with small crustaceous animals, and nourished, too, shells like those of our pearl-mussels. The land—so luxuriantly clothed with vegetable forms—was hummed over by beetles, chirupped over by grasshoppers and crickets, and crawled over by four-footed reptiles, that united in their structure the lizard and the frog. But of the general grade and proportions of its denizens we still remain in ignorance. From all that yet appears, the scenery of these forests must have been dark, silent, and gloomy, buried in a solitude that was startled by no tiger's roar, no cattle's low, and neither cheered with the melody of birds nor gladdened by the presence of man.
We have lingered, perhaps, too long over the remains of these old carboniferous animals. But the delay may be not without its use if, by thus bringing before us some of the more marked points in the structure of creatures that for ages peopled our planet, it broaden our view of creation; and by lifting the curtain from off a dim, distant period of our world's long history, it show, amid all diversities of arrangement, and all varieties of form, still the same grand principles of design, and the same modes of working as those which we can see and compare among the living forms around us. It is something to be assured that the race of man has been preceded by many other races, lower indeed in the scale of being, but manifesting, throughout the long centuries of their existence, ideas of mechanism and contrivance still familiar to us, and serving in this way to link the human era with those that have gone before, as parts of one grand scheme carried on by one great Creator.
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.
From the blackened plants that darkened the upper layers of the boulder, the transition was natural to the matrix in which they lay. The whole rock consisted of a fine quartzy sand more or less distinctly laminated, and showing in its lower parts well-rounded pebbles of quartz, green grit, and felspathic trap. The contemplation of these features suggested the existence of some old land with elevated ranges of hills, and wide verdant valleys traversed by rivulets and rivers which bore a ceaseless burden of mud, sand, and gravel, onwards to the sea. The pebbles afforded some indication of the kind of rocks that formed the hill-sides. Perhaps the higher grounds exhibited that grey wrinkled appearance peculiar to the quartz districts of the north-western Highlands, with here and there a bluff crag of felspathic trap shooting up from among the fern-brakes of the valley, or cutting across the channel of some mountain stream that tumbled over the pale rock in a sheet of foam. And there may have been among these uplands smooth undulating districts, dotted over with dark araucarian pines, and densely clothed with a brushwood of rolling fern, but which showed in all their ravines the green grit that formed the framework of the country,—its beds twisted and contorted, jointed and cleaved, like the grits and slates along the banks of many a stream, beloved by the angler, in the classic ground of the Ettrick and the Yarrow. But whatever may have been the special features of its scenery, there can be no doubt of the land's existence. The carbonized plants stand up to tell us of its strange and luxuriant vegetation. We have listened to their story, and suffered them to lead us away into forest, and lake, and sea, to look on the various forms of life, vegetable and animal, which abounded in that far-distant age. We return again to the boulder, and shall now seek to learn the lessons which the sand and pebbles have to teach us. Their subject belongs to what is called physical geology, and will bring before us some of the more mechanical operations of nature, such as the slow but constant action of air, rain, and rivers, upon hard rock, the grinding action of the waves, and the consequent accumulation of new masses of sedimentary rock.
In all the departments of nature that come under the cognizance of man, there is seen to be an endless succession of mutations. According to the Samian philosopher—
"Turn wheresoe'er we may by land or sea,