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tervals thin seams of coal, like those of Gaspé in Canada, which seemed to have resulted from the growth and drift of terrestrial vegetation. Wherever it occurs its sedimentary character is sufficiently apparent, and though frequently intersected by dykes and eruptive masses of basalt and felstone, its stratified arrangement is never wholly obliterated. The interstratifications of volcanic ash and igneous overflows observable in the Silurian system, and so frequent in the Carboniferous, are rarely witnessed in connection with the Old Red Sandstone, as if the period, in the north of Europe at least, had been one of comparative internal quiescence. The system occupies considerable areas in Europe, Asia, Africa, and both Americas, and is chiefly of marine formation, though in some districts the total absence of shells and corals would lead to the inference of freshwater conditions. If the Old Red Sandstone of Scotland be of marine origin, it seems inexplicable why no sea-shell, coral, or other zoophyte should have yet been detected in any of its strata. Numerous as its fishes and crustacea undoubtedly are, and gigantic as some of them may appear, they may have been inhabitants of estuaries or fresh-water seas; and though the general belief leans towards oceanic conditions, we are still without unmistakable proofs to support it.
We have said that the system occupies extensive areas both in the Old and New World, and as no two rivers carry down the same kind of debris, and no two seas receive exactly the same kind of sediments, there will be considerable diversity in the character of its rocks—that is, in colour, composition, and arrangement. Not only so, but as the system is often of great thickness (12,000 feet or more), there had been oscillations of the crust or new distributions of sea and land during the long period of its deposition, and thus its lower, middle, and upper portions differ even
in the same region, and sometimes lie unconformably upon each other. It is for this reason that geologists speak of the “Lower Old Red,” the “Middle Old Red,” and the “Upper Old Red,” — each series differing not only in the composition of its strata, but in the character of its fossil contents. But whatever its variations, there is, throughout Europe at least, a marked prevalence of reddish-coloured sandstones and slaty shales; hence the name “Red” in allusion to this colour, and the term “Old” because it lies beneath the coal-measures, and in contradistinction to another series of red sandstones (the New Red) that lies above them,-a distinction that was long ago made by the coal-miners of England. The system is also frequently termed the “ Devonian,” because a portion of it is well developed in Devonshire—a term chiefly introduced by Sir Roderick Murchison, to harmonise with his geographical nomenclature of Silurian and Permian. So much for name and mineral composition; let us now try to catch a glimpse of the physical conditions under which it was deposited, and the kind of life that peopled the land and waters.
Beyond a few scattered indications of the ancient distributions of sea and land, geology can obtain no more. One formation is so frequently overlaid by portions of later formations; so many portions have also been removed by waste and denudation; and perhaps still greater expanses are hidden by the ocean, which covers nearly three-fourths of the earth's known surface, that we can merely indicate by disconnected patches the seas in which they were deposited. In the case of the Old Red Sandstone, which occupies considerable areas both in the Old and New Worlds, we cannot trace either the extent or configuration of its seas, but we catch occasional glimpses of their shores in the conglomerates which must have formed their pebbly beaches, and in the worm-trails and burrows, the crustacean tracks, the rain-prints, and sun-cracks on the surface of the sandstones which must have then spread out as shallow and alternately-exposed sands. Strange revelations these of the olden sea-shore !—the ripple of the receding tide, the winding trail of the shell-fish, the burrow and sand-cast of the sea-worm, the patter of crustacean feet, the pittings of the rain-shower, and the irregular shrinkage cracks of the sunbaked shore-mud. And yet, as surely as these phenomena are witnessed on the muds of existing sea-creeks, so surely were they impressed on the shores of the Old Red Sandstone, were dried and hardened by the sun, covered over by newer sediments, and thus preserved through all time as evidences that nature's operations have been going forward much in the same way from the remotest of periods. But clear as these physical evidences are of the nature of the Old Red sea-shore, there are facts connected with the great extent and thickness of the pebbly (we may say bouldery) conglomerates that are not so easy of explanation. We know that in many parts of the world there are vast pebbly and shingly beaches, and that in some instances the rounded blocks are hundreds of pounds in weight; but there is something so peculiar in the aggregation of the Old Red conglomerates, with their striated pebbles, their irregular imbeddings of fine-grained sandstones and the like, that they suggest the idea of masses floated and packed up by shore-ice, and perhaps to some such condition their enormous accumulations may yet be ascribed.* Be this as it may, its usual sandstones, flagstones, slaty shales, clayey marls, and concretionary limestones are true water-formed strata, and we perceive in their numerous alternations and varying compositions the recurrent sediments of open and free-flowing seas, whether fresh-water or saline.
* Several years ago we appended the following note to a chapter on the Old Red Sandstone (*Past and Present Life of the Globe'), and see no reason yet to change our opinion :-“Whoever has examined the bouldery conglomerates of the Scottish Old Red, with their large irregular blocks, their peculiar unassorted aggregation, the nature of the cementing matrix, and the frequent 'nestings' or interlaminated patches of fine argillaceous sandstone, must have had suggested to his mind the idea of ice-action. And this notion must have been strengthened when
But if the mere lithological composition of its rocks can thus throw light on the geographical conditions of the Old Red Sandstone period, much more are we aided by a consideration of its fossils—the plant-life and animal-life that peopled the lands and waters. Wherever it has been examined, the flora appears to be of a lowly character-seaweeds, marsh or rush-like plants, clubmoss-like twigs, fronds of ferns, and less evidently, perhaps, drifted fragments of coniferous trees. We thus get a glimpse, as it were, of rocky weed-covered beaches, low marshy river-banks, of shady nooks and corners where fern and clubmöss luxuriate, and of higher uplands fitted for the growth of coniferæ or pine-like trees. So far as known in Europe, the plants of the Old Red generally appear in detached and drifted fragments, and rarely in such abundance as to form a bituminous or coaly shale; but in Canada the thin seams of coal discovered by Dr Dawson would indicate not only a greater luxuriance, but even land areas on which they grew and died till the accumulated masses were sufficient to form successive layers of pure and crystalline coal. This is all that we learn of the dry land of the period from the vegetation
he turned to the sandstones, and found them imbedding angular fragments of rock, shale, and even clay, which could scarcely have suffered transport unless enclosed in drifting ice-floes. The paucity of terrestrial life in certain areas seems also a further corroboration of the idea of glacial influences — a hypothesis which seems at first sight extremely probable, though requiring for its final demonstration a much more protracted and careful examination than the several phenomena have yet received from geologists." In working out this suggestion, the conglomerates between Stonehaven and Bervie, of Forfarshire, Perthshire, and Bute may be studied with advantage.
that clothed it. We know nothing of its extent or configuration, nothing of its hills and valleys, of its lakes or rivers, and are only left to infer from the nature and amount of the stratified sediments that the latter must have been both large and powerful. No true terrestrial creature—insect, reptile, bird, or mammal_has yet been detected in its strata; and all that we know of its fauna is strictly aquatic, and in all likelihood marine.
This fauna of the waters differs, of course, like the existing fauna, in different seas; but viewing the whole, and taking the entire range of the system through its lower, middle, and upper divisions, we have illustrations of the following zoological orders :—Corals, encrinites, and shells occur abundantly in the limestones of Devonshire, but similar organisms are altogether absent from the red sandstones of Hereford and Scotland, and to a great extent also. from the strata as developed in the north of Europe. Whether this has arisen from some peculiarity in the seabottom, or, as has been suggested, from the Scotch beds being chiefly of fresh-water origin, has not been satisfactorily determined; but the fact stands undoubted that up to the present time no trace of a coral, an echinoderm (star-fish or encrinite), or a shell-fish has been detected in the Old Red Sandstone of Scotland. With what portion of the Scottish beds the Devonshire strata may have been contemporaneously deposited has not yet been determined ; but clearly it was not with the lower flagstones and bouldery conglomerates of Perth and Forfar. The Devonian corals and encrinites imply waters of genial temperature; the bouldery conglomerates the reverse : and in all likelihood the two, though classed under the same system, were chronologically separated by ages.* But while the coral-building zoophytes,
* This is not, perhaps, the place to enter into the question of co-ordination; but we cannot refrain from repeating our conviction, expressed in