Some of the springs which issue from the ichthyolite beds along the shores of the Moray Frith are largely charged, not with 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, mechanically at 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, so interesting 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.)
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 the lower 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.
[CHAPTER XI.]
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.
Physiognomy is 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 upper stories 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.