[AU]There occurs in Mr. Murchison'sSilurian Systema singularly amusing account of one of the most unfortunate of all coal-boring enterprises; the unlucky projector, a Welsh farmer, having set himself to dig for coal in the lowest member of the system, at least six formations beneath the only one at which the object of his search could have been found. Mr. Murchison thus relates the story:—"At Tin-y-coed I found a credulous farmer ruining himself in excavating a horizontal gallery in search of coal, an ignorant miner being his engineer. The case may serve as a striking example of thecoal-boringmania in districts which cannot by possibility contain that mineral; and a few words concerning it may, therefore, prove a salutary warning to those who speculate for coal in the Silurian Rocks. The farmhouse of Tin-y-coed is situated on the sloping sides of a hill of trap, which throw off, upon its north-western flank, thin beds of black grauwacke shale, dipping to the west-north-west at a high angle. The color of the shale, and of the water that flowed down its sides, the pyritous veins, and other vulgar symptoms of coal-bearing strata, had long convinced the farmer that he possessed a large hidden mass of coal, and, unfortunately, a small fragment of real anthracite was discovered, which burnt like the best coal. Miners were sent for, and operations commenced. To sink a shaft was impracticable, both from the want of means, and the large volume of water. A slightly inclined gallery was therefore commenced, the mouth of which was opened at the bottom of the hill, on the side of the little brook which waters the dell. I have already stated that, in many cases, where the intrusive trap throws off the shale, the latter preserves its natural and unaltered condition to within a certain distance of the trap; and so it was at Tin-y-coed, for the level proceeded for 155 feet with little or no obstacle. Mounds of soft black shale attested the rapid progress of the adventurers, when suddenly they came to a 'change of metal.' They were now approaching the nucleus of the little ridge; and the rock they encountered was, as the men informed me, 'as hard as iron,' viz., of lydianized schist, precisely analogous to that which is exposed naturally in ravines where all the phenomena are laid bare. The deluded people, however, endeavored to penetrate the hardened mass, but the vast expense of blasting it put a stop to the undertaking, not, however, without a thorough conviction on the part of the farmer, that, could he but have got through that hard stuff, he would most surely have been well recompensed, for it was just thereabouts that they began to find 'small veins of coal.' It has been before shown, that portions of anthracite are not unfrequent in the altered shale, where it is in contact with the intrusive rock. And the occurrence of the smallest portion of anthracite is always sufficient to lead the Radnorshire farmer to suppose that he is very near 'El Dorado.' Amid all their failures, I never met with an individual who was really disheartened; a frequent exclamation being, 'O, if our squires were only men ofspirit, we should have as fine coal as any in the world!'"—(Silurian System, Part I., p. 328.)
[AU]There occurs in Mr. Murchison'sSilurian Systema singularly amusing account of one of the most unfortunate of all coal-boring enterprises; the unlucky projector, a Welsh farmer, having set himself to dig for coal in the lowest member of the system, at least six formations beneath the only one at which the object of his search could have been found. Mr. Murchison thus relates the story:—
"At Tin-y-coed I found a credulous farmer ruining himself in excavating a horizontal gallery in search of coal, an ignorant miner being his engineer. The case may serve as a striking example of thecoal-boringmania in districts which cannot by possibility contain that mineral; and a few words concerning it may, therefore, prove a salutary warning to those who speculate for coal in the Silurian Rocks. The farmhouse of Tin-y-coed is situated on the sloping sides of a hill of trap, which throw off, upon its north-western flank, thin beds of black grauwacke shale, dipping to the west-north-west at a high angle. The color of the shale, and of the water that flowed down its sides, the pyritous veins, and other vulgar symptoms of coal-bearing strata, had long convinced the farmer that he possessed a large hidden mass of coal, and, unfortunately, a small fragment of real anthracite was discovered, which burnt like the best coal. Miners were sent for, and operations commenced. To sink a shaft was impracticable, both from the want of means, and the large volume of water. A slightly inclined gallery was therefore commenced, the mouth of which was opened at the bottom of the hill, on the side of the little brook which waters the dell. I have already stated that, in many cases, where the intrusive trap throws off the shale, the latter preserves its natural and unaltered condition to within a certain distance of the trap; and so it was at Tin-y-coed, for the level proceeded for 155 feet with little or no obstacle. Mounds of soft black shale attested the rapid progress of the adventurers, when suddenly they came to a 'change of metal.' They were now approaching the nucleus of the little ridge; and the rock they encountered was, as the men informed me, 'as hard as iron,' viz., of lydianized schist, precisely analogous to that which is exposed naturally in ravines where all the phenomena are laid bare. The deluded people, however, endeavored to penetrate the hardened mass, but the vast expense of blasting it put a stop to the undertaking, not, however, without a thorough conviction on the part of the farmer, that, could he but have got through that hard stuff, he would most surely have been well recompensed, for it was just thereabouts that they began to find 'small veins of coal.' It has been before shown, that portions of anthracite are not unfrequent in the altered shale, where it is in contact with the intrusive rock. And the occurrence of the smallest portion of anthracite is always sufficient to lead the Radnorshire farmer to suppose that he is very near 'El Dorado.' Amid all their failures, I never met with an individual who was really disheartened; a frequent exclamation being, 'O, if our squires were only men ofspirit, we should have as fine coal as any in the world!'"—(Silurian System, Part I., p. 328.)
I have said that the waters of the well of the coal-heugh are chalybeate—a probable consequence of their infiltration through the iron oxides of the superior beds of the formation, and their subsequent passage through the deep red strata ofthe inferior bed. There could be very curious chapters written on mineral springs, in their connection with the formations through which they pass. Smollett's masterpiece, honest old Matthew Bramble, became thoroughly disgusted with the Bath waters on discovering that they filtered through an ancient burying-ground belonging to the Abbey, and that much of their peculiar taste and odor might probably be owing to the "rotten bones and mouldering carcasses" through which they were strained. Some of the springs of the Old Red Sandstone have also the churchyard taste, but the bones and carcasses through which they strain are much older than those of the Abbey burying-ground at Bath. The bitumenof the strongly impregnated rocks and clay-beds of this formation, like the bitumen of the still more strongly impregnated limestones and shales of the Lias, seems to have had rather an animal than vegetable origin. The shales of the Eathie Lias burn like turf soaked in oil, and yet they hardly contain one per cent, of vegetable matter. In a single cubic inch, however, I have counted about eighty molluscous organisms, mostly ammonites, and minute striated scallops; and the mass, when struck with the hammer, still yields the heavy odor of animal matter in a state of decay. The lower fish-beds of the Old Red are, in some localities, scarcely less bituminous. The fossil scales and plates, which they enclose, burn at the candle; they contain small cavities filled with a strongly scented, semi-fluid bitumen, as adhesive as tar, and as inflammable; and for many square miles together the bed is composed almost exclusively of a dark-colored, semi-calcareous, semi-aluminous schist, scarcely less fetid, from the great quantity of this substance which it contains, than the swine-stones of England. Its vegetable remains bear but a small proportion to its animal organisms; and from huge accumulations of these last decomposing amid the mud of a still sea, little disturbed by tempests or currents, and then suddenly interred by some widely spread catastrophe, to ferment and consolidate under vast beds of sand and conglomerate, the bitumen[AV]seems to have been elaborated. These bituminous schists, largely charged with sulphuret of iron, run far into the interior, along the flanks of the gigantic BenNevis, and through the exquisitely pastoral valley of Strathpeffer. The higher hills which rise over the valley are formed mostly of the great conglomerate—Knockferril, with its vitrified fort—the wooded and precipitous ridge over Brahan—and the middle eminences of the gigantic mountain on the north; but the bottom and the lower slopes of the valley are occupied by the bituminous and sulphureous schists of the fish-bed, and in these, largely impregnated with the peculiar ingredients of the formation, the famous medicinal springs of the Strath have their rise. They contain, as shown by chemical analysis, the sulphates of soda, of lime, of magnesia, common salt, and, above all, sulphuretted hydrogen gas—elements which masses of sea-mud, charged with animal matter, would yield as readily to the chemist as the medicinal springs of Strathpeffer. Is it not a curious reflection, that the commercial greatness of Britain, in the present day, should be closely connected with the towering and thickly spread forests of arboraceous ferns and gigantic reeds—vegetables of strange form and uncouth names—which flourished and decayed on its surface, age after age, during the vastly extended term of the carboniferous period, ere the mountains were yet upheaved, and when there was as yet no man to till the ground? Is it not a reflection equally curious, that the invalids of the present summer should be drinking health, amid the recesses of Strathpeffer, from the still more ancient mineral and animal debris of the lower ocean of the Old Red Sandstone, strangely elaborated for vast but unreckoned periods in the bowels of the earth? The fact may remind us of one of the specifics of a now obsolete school of medicine, which flourished in this country about two centuries ago, and which included in itsmateria medicaportions of the human frame. Among these was the flesh of Egyptian mummies, impregnated with the embalming drugs—the dried muscles and sinews of human creatures who had walked in the streets of Thebes or of Luxor three thousand years ago.
[AV]"In the slaty schists of Seefeld, in the Tyrol," say Messrs. Sedgwick and Murchison, "there is such an abundance of a similar bitumen, that it is largely extracted for medicinal purposes."—(Geol. Trans. for 1829, p. 134.)
[AV]"In the slaty schists of Seefeld, in the Tyrol," say Messrs. Sedgwick and Murchison, "there is such an abundance of a similar bitumen, that it is largely extracted for medicinal purposes."—(Geol. Trans. for 1829, p. 134.)
The commoner mineral springs of the formation, as might be anticipated, from the very general diffusion of the oxide to which it owes its color, are chalybeate. There are districts in Easter-Ross and the Black Isle in which the traveller scarcely sees a runnel by the way-side that is not half choked up by its fox-colored coagulum of oxide. Two of the most strongly impregnated chalybeates with which I am acquainted gush out of a sandstone bed, a few yards apart, among the woods of Tarbat House, on the northern shore of the Frith of Cromarty. They splash among the pebbles with a half-gurgling, half-tinkling sound, in a solitary but not unpleasing recess, darkened by alders and willows; and their waters, after uniting in the same runnel, form a little, melancholy lookinglochan, matted over with weeds, and edged with flags and rushes, and which swarms in early summer with the young of the frog in its tadpole state, and in the after months with the black water-beetle and the newt. The circumstance is a somewhat curious one, as the presence of iron as an oxide has been held so unfavorable to both animal and vegetable life, that the supposed poverty of the Old Red Sandstone in fossil remains has been attributed to its almost universal diffusion at the period the deposition was taking place. Were the system as poor as has been alleged, however, it might be questioned, on the strength of a fact such as this, whether the iron militated so much against the living existences of the formation, as against the preservation of their remains when dead.
Some of the springs which issue from the ichthyolite beds along the shores of the Moray Frith are largely charged, notwith iron, like the well of the coal-heugh, or the springs of Tarbat House, nor yet with hydrogen and soda, like the spa of Strathpeffer, but with carbonate of lime. When employed for domestic purposes, they choke up, in a few years, with a stony deposition, the spouts of tea-kettles. On a similar principle, they plug up their older channels, and then burst out in new ones; nor is it uncommon to find among the cliffs little hollow recesses, long since divested of their waters by this process, that are still thickly surrounded by coral-like incrustations of moss and lichens, grass and nettle-stalks, and roofed with marble-like stalactites. I am acquainted with at least one of these springs of very considerable volume, and dedicated of old to an obscure Roman Catholic saint, whose name it still bears, (St. Bennet,) which presents phenomena not unworthy the attention of the young geologist. It comes gushing from out the ichthyolite bed, where the latter extends, in the neighborhood of Cromarty, along the shores of the Moray Frith; and after depositing in a stagnant morass an accumulation of a grayish-colored and partially consolidated travertin, escapes by two openings to the shore, where it is absorbed among the sand and gravel. A storm about three years ago swept the beach several feet beneath its ordinary level, and two little moles of conglomerate and sandstone, the work of the spring, were found to occupy the two openings. Each had its fossils—comminuted sea-shells, and stalks of hardened moss; and in one of the moles I found imbedded a few of the vertebral joints of a sheep. It was a recent formation on a small scale, bound together by a calcareous cement furnished by the fish-beds of the inferior Old Red Sandstone, and composed of sand and pebbles, mostly from the granitic gneiss of the neighboring hill, and organisms, vegetable and animal, from both the land and the sea.
The Old Red Sandstone of Scotland has been extensively employed for the purposes of the architect, and its limestones occasionally applied to those of the agriculturist. As might be anticipated in reference to a deposit so widely spread, the quality of both its sandstones and its lime is found to vary exceedingly in even the same beds when examined in different localities. Its inferior conglomerate, for instance, in the neighborhood of Cromarty, weathers so rapidly, that a fence built of stones furnished by it little more than half a century ago, has mouldered in some places into a mere grass-covered mound. The same bed in the neighborhood of Inverness is composed of a stone nearly as hard and quite as durable as granite, and which has been employed in paving the streets of the place—a purpose which it serves as well as any of the igneous or primary rocks could have done. At Redcastle, on the northern shore of the Frith of Beauly, the same conglomerate assumes an intermediate character, and forms, though coarse, an excellent building stone, which, in some of the older ruins of the district, presents the marks of the tool as sharply indented as when under the hands of the workman. Some of the sandstone beds of the system are strongly saliferous; and these, however coherent they may appear, never resist the weather until first divested of their salt. The main ichthyolite bed on the northern shore of the Moray Frith is overlaid by a thick deposit of a finely-tinted yellow sandstone of this character, which, unlike most sandstones of a mouldering quality, resists the frosts and storms of winter, and wastes only when the weather becomes warm and dry. A few days of sunshine affect it more than whole months of high winds and showers. The heat crystallizes at the surface the salt which it contains; the crystals, acting as wedges, throw off minute particles of the stone; and thus, mechanicallyat least, the degrading process is the same as that to which sandstones of a different but equally inferior quality are exposed during severe frosts. In the course of years, however, this sandstone, when employed in building, loses its salt; crust after crust is formed on the surface, and either forced off by the crystals underneath, or washed away by the rains; and then the stone ceases to waste, and gathers on its weathered inequalities a protecting mantle of lichens.[AW]The most valuable quarries in the Old Red System of Scotland yet discovered, are the flagstone quarries of Caithness and Carmylie. The former have been opened in the middle schists of the lower, or Tilestone formation of the system; the latter, as I have had occasion to remark oftener than once, in the Cornstone, or middle formation. The quarries of both Carmylie and Caithness employ hundreds of workmen, and their flagstones form an article of commerce. The best building-stone of the north of Scotland—best both for beauty and durability—is a pure Quartzose Sandstone furnished by the upper beds of the system. These are extensively quarried in Moray, near the village of Burghead, and exported to all parts of the kingdom. The famous obelisk of Forres, sointeresting to the antiquary—which has been described by some writers as formed of a species of stone unknown in the district, and which, according to a popular tradition, was transported from the Continent—is evidently composed of this Quartzose Sandstone, and must have been dug out of one of the neighboring quarries. And so coherent is its texture, that the storms of, perhaps, ten centuries have failed to obliterate its rude but impressive sculptures.
[AW]When left to time the process is a tedious one, and, ere its accomplishment, the beauty of the masonry is always in some degree destroyed. The following passage, from a popular work, points out a mode by which it might possibly be anticipated, and the waste of surface prevented:—"A hall of which the walls were constantly damp, though every means were employed to keep them dry, was about to be pulled down, when M. Schmithall recommended, as a last resource, that the walls should be washed with sulphuric acid, (vitriol.) It w T as done, and the deliquescent salts being decomposed by acid, the walls dried, and the hall was afterwards free from dampness."—(Recreations in Science.)
[AW]When left to time the process is a tedious one, and, ere its accomplishment, the beauty of the masonry is always in some degree destroyed. The following passage, from a popular work, points out a mode by which it might possibly be anticipated, and the waste of surface prevented:—"A hall of which the walls were constantly damp, though every means were employed to keep them dry, was about to be pulled down, when M. Schmithall recommended, as a last resource, that the walls should be washed with sulphuric acid, (vitriol.) It w T as done, and the deliquescent salts being decomposed by acid, the walls dried, and the hall was afterwards free from dampness."—(Recreations in Science.)
The limestones of both the upper and lower formations of the system have been wrought in Moray with tolerable success. In both, however, they contain a considerable per centage of siliceous and argillaceous earth. The system, though occupying an intermediate place between two metalliferous deposits,—the grauwacke and the carboniferous limestone,—has not been found to contain workable veins any where in Britain, and in Scotland no metallic veins of any kind, with the exception of here and there a few slender threads of ironstone, and here and there a few detached crystals of galena. Its wealth consists exclusively in building and paving stone, and in lime. Some of the richest tracts of corn land in the kingdom rest on the Old Red Sandstone—the agricultural valley of Strathmore, for instance, and the fertile plains of Easter-Ross: Caithness has also its deep, corn-bearing soils, and Moray has been well known for centuries as the granary of Scotland. But in all these localities the fertility seems derived rather from an intervening subsoil of tenacious diluvial clay, than from the rocks of the system. Wherever the clay is wanting, the soil is barren. In the moor of the Milbuy,—a tract about fifty square miles in extent, and lying within an hour's walk of the Friths of Cromarty and Beauly,—a thin covering of soil rests on the sandstones of thelower formation. And so extreme is the barrenness of this moor, that notwithstanding the advantages of its semi-insular situation, it was suffered to lie as an unclaimed common until about twenty-five years ago, when it was parcelled out among the neighboring proprietors.
Geological Physiognomy.—Scenery of the Primary Formations; Gneiss, Mica Schist, Quartz Rock.—Of the Secondary; the Chalk Formations, the Oolite, the New Red Sandstone, the Coal Measures.—Scenery in the Neighborhood of Edinburgh.—Aspect of the Trap Rocks.—The Disturbing and Denuding Agencies.—Distinctive Features of the Old Red Sandstone.—Of the Great Conglomerate.—Of the Ichthyolite Beds.—The Burn of Eathie.—The Upper Old Red Sandstones.—Scene in Moray.
Physiognomyis no idle or doubtful science in connection with Geology. The physiognomy of a country indicates, almost invariably, its geological character. There is scarce a rock among the more ancient groups that does not affect its peculiar form of hill and valley. Each has its style of landscape; and as the vegetation of a district depends often on the nature of the underlying deposits, not only are the main outlines regulated by the mineralogy of the formations which they define, but also in many cases the manner in which these outlines are filled up. The coloring of the landscape is well nigh as intimately connected with its Geology as the drawing. The traveller passes through a mountainous region of gneiss. The hills, which, though bulky, are shapeless, raise their huge backs so high over the brown, dreary moors, which, unvaried by precipice or ravine, stretch away for miles from their feet, that even amid the heats of midsummer the snow gleams in streaks and patches from their summits. And yet so vast is their extent of base, and their tops so truncated, that they seem but half-finished hills notwithstanding—hills interdicted somehow in the forming, and the work stopped ere the upperstories had been added. He pursues his journey, and enters a district of micaceous schist. The hills are no longer truncated, or the t moors unbroken; the heavy ground-swell of the former landscape has become a tempestuous sea, agitated by powerful winds and conflicting tides. The picturesque and somewhat fantastic outline is composed of high, sharp peaks, bold, craggy domes, steep, broken acclivities, and deeply serrated ridges; and the higher hills seem as if set round with a framework of props and buttresses, that stretch out on every side like the roots of an ancient oak. He passes on, and the landscape varies; the surrounding hills, though lofty, pyramidal, and abrupt, are less rugged than before; and the ravines, though still deep and narrow, are walled by ridges no longer serrated and angular, but comparatively rectilinear and smooth. But the vegetation is even more scanty than formerly; the steeper slopes are covered with streams of debris, on which scarce a moss or lichen finds root; and the conoidal hills, bare of soil from their summits half way down, seem so many naked skeletons, that speak of the decay and death of nature. All is solitude and sterility. The territory is one of Quartz rock. Still the traveller passes on: the mountains sink into low swellings; long rectilinear ridges run out towards the distant sea, and terminate in bluff, precipitous headlands. The valleys, soft and pastoral, widen into plains, or incline in long-drawn slopes of gentlest declivity. The streams, hitherto so headlong and broken, linger beside their banks, and then widen into friths and estuaries. The deep soil is covered by a thick mantle of vegetation—by forest trees of largest growth, and rich fields of corn; and the solitude of the mountains has given place to a busy population. He has left behind him the primary regions, and entered on one of the secondary districts.
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 lakeor 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 thesame 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 readera 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 openingsof 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 andthere 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. TheGaylet 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. TheGaylet Potseems 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 isless 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.
[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 ridgeshould 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.
Let us take another view of this section. It stretches between two of the granitic knobs or wedges to which I have had such frequent occasion to refer—the Southern Sutor of Cromarty, and the Hill of Eathie; and the edges of the strata somewhat remind one of the edges of a bundle of deals laid flatways on two stones, and bent towards the middle by their own weight. But their more brittle character is shown by the manner in which their ends are broken and uptilted against the granitic knobs on which they seem to rest; and towards the western knob the whole bundle has been broken across from below, and the opening occasioned by the fracture forms a deep, savage ravine, skirted by precipices, that runs far into the interior, and exhibits the lower portion of the system to well nigh its base. Will the reader spend a very few minutes in exploring the solitary recesses of this rocky trench—it matters not whether as a scene-hunter or a geologist? We pass onwards along the beach through the middle line of the denuded hollow. The natural rampart that rises on the right ascends towards the uplands in steep slopes, lined horizontally by sheep-walks, and fretted by mossy knolls, and churchyard-like ridges—or juts out into abrupt and weathered crags, crusted with lichens and festooned with ivy—or recedes into bosky hollows, roughened by the sloe-thorn, the wild-rose, and the juniper; on the left the wide extent of the Moray Frith stretches out to the dim horizon, with its vein-like currents, and its undulating lines of coast; while before us wesee, far in the distance, the blue vista of the Great Valley, with its double wall of jagged and serrated hills, and directly in the opening, the gray, diminished spires of Inverness. We reach a brown, mossy stream, of just volume enough to sweep away the pebbles and shells that have been strewed in its course by the last tide; and see, on turning a sudden angle, the precipices cleft to their base by the ravine that has yielded its waters a passage from the interior.
We enter along the bed of the stream. A line of mural precipices rises on either hand—here advancing in ponderous overhanging buttresses, there receding into deep, damp recesses, tapestried with ivy, and darkened with birch and hazel. A powerful spring, charged with lime, comes pouring by a hundred different threads over the rounded brow of a beetling crag, and the decaying vegetation around it is hardening into stone. The cliffs vary their outline at every step, as if assuming in succession, all the various combinations of form that constitute the wild and the picturesque; and the pale hues of the stone seem, when brightened by the sun, the very tints a painter would choose to heighten the effect of his shades, or to contrast most delicately with the luxuriant profusion of bushes and flowers that wave over the higher shelves and crannies. A colony of swallows have built from time immemorial under the overhanging strata of one of the loftier precipices; the fox and badger harbor in the clefts of the steeper and more inaccessible banks. As we proceed, the deli becomes wilder and more deeply wooded; the stream frets and toils at our feet—here leaping over an opposing ridge;—there struggling in a pool—yonder escaping to the light from under some broken fragment of cliff. There is a richer profusion of flowers, a thicker mantling of ivy and honeysuckle; and after passing a semicircular inflection of the bank, that wavesfrom base to summit with birch, hazel, and hawthorn, we find the passage shut up by a perpendicular wall of rock about thirty feet in height, over which the stream precipitates itself, in a slender column of foam, into a dark, mossy basin. The long arms of an intermingled clump of birches and hazels stretch half way across, tripling with their shade the apparent depth of the pool, and heightening in an equal ratio the white flicker of the cascade, and the effect of the bright patches of foam which, flung from the rock, incessantly revolve on the eddy.
Mark now the geology of the ravine. For about half way from where it opens to the shore, to where the path is obstructed by the deep mossy pool and the cascade, its precipitous sides consist of three bars or stories. There is first, reckoning from the stream upwards, a broad bar of pale red; then a broad bar of pale lead color; last and highest, a broad bar of pale yellow; and above all, there rises a steep green slope, that continues its ascent till it gains the top of the ridge. The middle, lead-colored bar is an ichthyolite bed, a place of sepulture among the rocks, where the dead lie by myriads. The yellow bar above is a thick bed of saliferous sandstone. We may see the projections on which the sun has beat most powerfully covered with a white crust of salt; and it may be deemed worthy of remark, in connection with the circumstance, that its shelves and crannies are richer in vegetation than those of the other bars. The pale red bar below is composed of a coarser and harder sandstone, which forms an upper moiety of the arenaceous portion of the great conglomerate. Now mark, further, that on reaching a midway point between the beach and the cascade, this triple-barred line of precipices abruptly terminates, and a line of precipices of coarse conglomerate as abruptly begins. I occasionallypass a continuous wall, built at two different periods, and composed of two different kinds of materials: the one half of it is formed of white sandstone, the other half of a dark-colored basalt; and the place where the sandstone ends and the basalt begins is marked by a vertical line, on the one side of which all is dark colored, while all is of a light color on the other. Equally marked and abrupt is the vertical line which separates the triple-barred from the conglomerate cliffs of the ravine of Eathie. The ravine itself may be described as a fault in the strata; but here is a fault, lying at right angles with it, on a much larger scale: the great conglomerate on which the triple bars rest has been cast up at least two hundred feet, and placed side by side with them. And yet the surface above bears no trace of the catastrophe. Denuding agencies of even greater power than those which have hollowed out the cliffs of the neighboring coast, or whose operations have been prolonged through periods of even more extended duration, have ground down the projected line of the upheaved mass to the level of the undisturbed masses beside it. Now, mark further, as we ascend the ravine, that the grand cause of the disturbance appears to illustrate, as it were, and that very happily, the manner in which the fault was originally produced. The precipice, over which the stream leaps at one bound into the mossy hollow, is composed of granitic gneiss, and seems evidently to have intruded itself, with much disturbance, among the surrounding conglomerate and sandstones. A few hundred yards higher up the dell, there is another much loftier precipice of gneiss, round which we find the traces of still greater disturbance; and, higher still, yet a third abrupt precipice of the same rock. The gneiss rose, trap-like, in steps, and carried up the sandstone before it in detached squares. Each step has itsanswering fault immediately over it; and the fault where the triple bars and the conglomerate meet is merely a fault whose step of granitic gneiss stopped short ere it reached the surface. But the accompanying section (see Frontispiece, sect. 4) will better illustrate the geology of this interesting ravine, than it can be illustrated by any written description. I may remark, ere taking leave of it, however, that its conglomerates exhibit a singularly large amount of false stratification at an acute angle with the planes of the real strata, and that a bed of mouldering sandstone near the base of the system may be described, from its fissile character, as a tilestone.[AY]