The Old Red Sandstone; or, New Walks in an Old Field

by Hugh Miller

And these less rugged formations have also their respective styles—marred and obliterated often by the Plutonic agency, which imparts to them in some instances its own character, and in some an intermediate one, but in general distinctly marked, and easily recognized. The Chalk presents its long inland lines of apparent coast, that send out their rounded headlands, cape beyond cape, into the wooded or corn-covered plains below. Here and there, there juts up at the base of the escarpement a white, obelisk-like stack; here and there, there opens into the interior a narrow, grassy bay, in which noble beeches have cast anchor. There are valleys without streams; and the landscape a-top is a scene of arid and uneven downs, that seem to rise and fall like the sea after a storm. We pass on to the Oolite: the slopes are more gentle, the lines of rising ground less continuous, and less coast-like; the valleys have their rivulets, and the undulating surface is covered by a richer vegetation. We enter on a district of New Red Sandstone. Deep, narrow ravines intersect elevated platforms. There are lines of low precipices, so perpendicular and so red, that they seem as if walled over with new brick; and here and there, amid the speckled and mouldering sandstones, that gather no covering of lichen, there stands up a huge, altar-like mass of lime, mossy and gray, as if it represented a remoter antiquity than the rocks around it. The Coal Measures present often the appearance of vast lakes frozen over during a high wind, partially broken afterwards by a sudden thaw, and then frozen again. Their shores stand up around them in the form of ridges and mountain chains of the older rocks; and their surfaces are grooved into flat valleys and long lines of elevation. Take, as an instance, the scenery about Edinburgh. The Ochil Hills and the Grampians form the distant shores of the seeming lake or basin on the one side, the range of the Lammermuirs and the Pentland group on the other; the space between is ridged and furrowed in long lines, that run in nearly the same direction from north-east to south-west, as if, when the binding frost w r as first setting in, the wind had blown from off the northern or southern shore.

But whence these abrupt, precipitous hills that stud the landscape, and form, in the immediate neighborhood of the city, its more striking features? They belong—to return to the illustration of the twice-frozen lake—to the middle period of thaw, when the ice broke up; and, as they are composed chiefly of matter ejected from the abyss, might have characterized equally any of the other formations. Their very striking forms, however, illustrate happily the operations of the great agencies on which, in the secondary and transition deposits, all the peculiarities of scenery depend. The molten matter from beneath seems to have been injected, in the first instance, through rents and fissures among the carboniferous shales and sandstones of the district, where it lay cooling in its subterranean matrices, in beds and dikes, like metal in the moulds of the founder; and the places which if occupied must have been indicated on the surface but by curves and swellings of the strata. The denuding power then came into operation in the form of tides and currents, and ground down the superincumbent rocks. The injected masses, now cooled and hardened, were laid bare; and the softer framework of the moulds in which they had been cast was washed from their summits and sides, except where long ridges remained attached to them in the lines of the current, as if to indicate the direction in which they had broken its force. Every larger stone in a water-course, after the torrent fed by a thunder shower has just subsided, shows, on the same principle, its trail of sand and shingle piled up behind it. The outlines of the landscape were modified yet further by the yielding character of the basement of sandstone or shale on which the Plutonic beds so often rest. The basement crumbled away as the tides and waves broke against it. The injected beds above, undermined in the process, and with a vertical cleavage, induced by their columnar tendency, fell down in masses that left a front perpendicular as a wall. Each bed came thus to present its own upright line of precipice; and hence—when they rise bed above bed, as often occurs—the stair-like outline of hill to which the trap rocks owe their name; hence the outline of the Dalmahoy Crags, for instance, and of the southern and western front of Salisbury Crags.

In all the sedimentary formations the peculiarities of scenery depend on three circumstances—on the Plutonic agencies, the denuding agencies, and the manner and proportions in which the harder and softer beds of the deposits on which these operated alternate with one another. There is an union of the active and the passive in the formation of landscape; that which disturbs and grinds down, and that which, according to its texture and composition, affects, if I may so speak, a peculiar style of being ground down and disturbed; and it is in the passive circumstances that the peculiarities chiefly originate, Hence it is that the scenery of the Chalk differs from the scenery of the Oolite, and both from that of the Coal Measures. The Old Red Sandstone has also its peculiarities of prospect, which vary according to its formations, and the amount and character of the disturbing and denuding agencies to which these have been exposed. Instead, however, of crowding its various, and, in some instances, dissimilar features into one landscape, I shall introduce to the reader a few of its more striking and characteristic scenes, as exhibited in various localities, and by different deposits, beginning first with its conglomerate base.

The great antiquity of this deposit is unequivocally indicated by the manner in which we find it capping, far in the interior, in insulated beds and patches, some of our loftier hills, or, in some instances, wrapping them round, as with a caul, from base to summit. It mixes largely, in our northern districts, with the mountain scenery of the country, and imparts strength and boldness of outline to every landscape in which it occurs. Its island-like patches affect generally a bluff parabolic or conical outline; its loftier hills present rounded, dome-like summits, which sink to the plain on the one hand in steep, slightly concave lines, and on the other in lines decidedly convex, and a little less steep. The mountain of boldest outline in 'the line of the Caledonian Valley (Mealforvony) is composed externally of this rock. Except where covered by the diluvium, it seems little friendly to vegetation. Its higher summits are well nigh as bare as those of the primary rocks; and when a public road crosses its lower ridges, the traveller generally finds that there is no paving process necessary to procure a hardened surface, for his wheels rattle over the pebbles embedded in the rock. On the sea-coast, in several localities, the deposit presents striking peculiarities of outline. The bluff and rounded precipices stand out in vast masses, that affect the mural form, and present few of the minuter angularities of the primary rocks. Here and there a square buttress of huge proportions leans against the front of some low-browed crag, that seems little to need any such support, and casts a length of shadow athwart its face. There opens along the base of the rock a line of rounded, shallow caves, or what seem rather the openings of caves not yet dug, and which testify of a period when the sea stood about thirty feet higher on our coasts than at present. A multitude of stacks and tabular masses lie grouped in front, perforated often by squat, heavy arches; and stacks, caverns, buttresses, crags, and arches, are all alike mottled over by the thickly-set and variously colored pebbles. There is a tract of scenery of this strangely marked character in the neighborhood of Dunottar, and two other similar tracts in the far north, where the hill of Nigg, in Ross-shire, declines towards the Lias deposit in the Bay of Shandwick, and where, in the vicinity of Inverness, a line of bold, precipitous coast runs between the pyramidal wooded eminence which occupies the south-eastern corner of Ross, and the tower-like headlands that guard the entrance of the Bay of Munlochy. In the latter tract, however, the conglomerate is much less cavernous than in the other two.

The sea-coast of St. Vigeans, in Forfarshire, has been long celebrated for its romantic scenery and its caves; and though it belongs rather to the conglomerate base of the upper formation than to the great conglomerate base of the lower, it is marked, from the nature of the materials—materials common to both—by features indistinguishable from those which characterize the sea-coasts of the older deposit. Its wall of precipices averages from a hundred to a hundred and eighty feet in height—no very great matter compared with some of our northern lines, but the cliffs make up for their want of altitude by their bold and picturesque combinations of form; and I scarce know where a long summer's day could well be passed more agreeably than among their wild and solitary recesses. The incessant lashings of the sea have ground them down into shapes the most fantastic. Huge stacks, that stand up from amid the breakers, are here and there perforated by round, heavy-browed arches, and cast the morning shadows inland athwart the cavern-hollowed precipices behind. The never-ceasing echoes reply, in long and gloomy caves, to the wild tones of the sea. Here a bluff promontory projects into the deep, green water, and the white foam, in times of tempest, dashes up a hundred feet against its face. There a narrow strip of vegetation, spangled with wild flowers, intervenes between the beach and the foot of the cliffs that sweep along the bottom of some semicircular bay; but we see, from the rounded caves by which they are studded, and the polish which has blunted their lower angularities, that at some early period the breakers must have dashed for ages against their bases. The Gaylet Pot, a place of interest, from its very striking appearance, to more than geologists, is connected with one of the deep-sea promontories. We see an oblong hollow in the centre of a corn-field, that borders on the cliffs. It deepens as we approach it, and on reaching the edge we find ourselves standing on the verge of a precipice about a hundred and fifty feet in depth, and see the waves dashing along the bottom. On descending by a somewhat precarious path, we find that a long, tunnel-like cavern communicates with the sea, and mark, through the deep gloom of the passage, the sunlight playing beyond; and now and then a white sail passing the opening, as if flitting across the field of a telescope. The Gaylet Pot seems originally to have been merely a deep, straight cave, hollowed in the line of a fault by the waves; and it owes evidently its present appearance to the falling in of the roof for about a hundred yards, at its inner extremity.

We pass from the conglomerate to the middle and upper beds of the lower formation, and find scenery of a different character in the districts in which they prevail. The aspect is less bold and rugged, and affects often long horizontal lines, that stretch away without rise or depression, amid the surrounding inequalities of the landscape for miles and leagues, and that decline to either side, like roofs of what the architect would term a low pitch. The ridge of the Leys in the eastern opening of the Caledonian Valley, so rectilinear in its outline, and so sloping in its sides, presents a good illustration of this peculiarity. The rectilinear ridge which runs from the Southern Sutor of Cromarty far into the interior of the country, and which has been compared in a former chapter to the shaft of a spear, furnishes another illustration equally apt.[AX] Where the sloping sides of these roof-like ridges decline, as in the latter instance, towards an exposed sea-coast, we find the slope terminating often in an abrupt line of rock dug out by the waves. It is thus a roof set on walls, and furnished with eaves. A ditch just finished by the laborer presents regularly sloping sides; but the little stream that comes running through gradually widens its bed by digging furrows into the slopes, the undermined masses fall in and are swept away, and, in the course of a few months, the sides are no longer sloping, but abrupt. And such, on a great scale, has been the process through which coast-lines that were originally paved slopes have become walls of precipices. The waves cut first through the outer strata; and every stratum thus divided comes to present two faces—a perpendicular face in the newly-formed line of precipice, and another horizontal face lying parallel to it, along the shore. One half the severed stratum seems as if rising out of the sea, the other half as if descending from the hill: the geologist who walks along the beach finds the various beds presented in duplicate—a hill-bed on the one side, and a sea-bed on the other. There occurs a very interesting instance of this arrangement in the bold line of coast on the northern shore of the Moray Frith, so often alluded to in a previous chapter, as extending between the Southern Sutor and the Hill of Eathie; and which forms the wall of a portion of the roof-like ridge last described. The sea first broke in a long line through strata of red and gray shale, next through a thick bed of pale-yellow stone, then through a continuous bed of stratified clays and nodular limestone, and, last of all, through a bed, thicker than any of the others, of indurated red sandstone. The line of cliffs formed in this way rises abruptly for about a hundred yards on the one hand; the shore stretches out for more than double the same space on the other; on both sides the beds exactly correspond; and to ascend in the line of the strata from the foot of the cliffs, we have either to climb the hill, or to pass downwards at low ebb to the edge of the sea. The section is of interest, not only from the numerous organisms, animal and vegetable, which its ichthyolite beds contain, but from the illustration which it also furnishes of denudation to a vast extent from causes still in active operation. A line of precipices a hundred yards in height, and more than two miles in length, has been dug out of the slope by the slow wear of the waves, in the unreckoned course of that period during which the present sea was bounded in this locality by the existing line of coast. (See Frontispiece, sect. 3.)

[AX] The valleys which separate these ridges form often spacious friths and bays, the frequent occurrence of which in the Old lied Sandstone constitutes, in some localities, one of the characteristics of the system. Mark in a map of the north of Scotland, how closely friths and estuaries lie crowded together between the counties of Sutherland and Inverness. In a line of coast little more than forty miles in extent, there occur four arms of the sea—the Friths of Cromarty, Beauly, and Dornoch, and the Bay of Munlochy. The Frith of Tay and the Basin of Montrose are also semi-marine valleys of the Old Red Sandstone. Two of the finest harbors in Britain, or the world, belong to it—Milford Haven, in South Wales, and the Bay of Cromarty.

I know not a more instructive walk for the young geologist than that furnished by the two miles of shore along which this section extends. Years of examination and inquiry would fail to exhaust it. It presents us, I have said, with the numerous organisms of the Lower Old Red Sandstone; it presents us also, towards its western extremity, with the still more numerous organisms of the Lower and Upper Lias; nor are the inflections and faults which its strata exhibit less instructive than its fossils or its vast denuded hollow. I have climbed along its wall of cliffs during the height of a tempestuous winter tide, when waves of huge volume, that had begun to gather strength under the night of the Northern Ocean, were bursting and foaming below; and as the harder pebbles, uplifted by the surge, rolled by thousands and tens of thousands along the rocky bottom, and the work of denudation went on, I have thought of the remote past, when the same agents had first begun to grind down the upper strata, whose broken edges now projected high over my head on the one hand, and lay buried far under the waves at my feet on the other. Almost all mountain chains present their abrupter escarpements to the sea, though separated from it in many instances by hundreds of miles—a consequence, it is probable, of a similar course of denudation, ere they had attained their present altitude, or the plains at their feet had been elevated over the level of the ocean. Had a rise of a hundred feet taken place in this northern district in the days of Cæsar, the whole upper part of the Moray Frith would have been laid dry, and it would now have seemed as inexplicable that this roof-like ridge should present so rugged a line of wall to the distant sea, as that the Western Ghauts of India should invariably turn their steepest declivities to the basin of the Indian Ocean, or that, from the Arctic Circle to the southern extremity of Patagonia, the huge mountain-chain of America should elevate its dizzy precipices in the line of the Pacific.