"The bleak, bare gneiss, with its monotonous undulations, tarns, and bogs, is surmounted by groups of cones, which for individuality of form and independence of position better deserve to be called mountains than most of the eminences to which that name is given in Scotland. These huge pyramids, rising to heights of between two thousand and four thousand feet, consist of dark red strata, so little inclined that their edges can be traced by the eye in long, level bars on the steeper hillsides and precipices, like lines of masonry. Here and there the hand of time has rent them into deep rifts, from which long 'screes' (slopes of loose stones) descend into the plains below, as stones are detached from the shivered walls of an ancient battlement. Down their sides, which have in places the steepness of a bastion, vegetation finds but scanty room along the projecting ledges of the sandstone beds, where the heath and grass and wildflowers cluster over the rock in straggling lines and tufts of green; and yet, though nearly as bare as the gneiss below them, these lofty mountains are far from presenting the same aspect of barrenness. The prevailing colour of their component strata gives them a warm red hue, which even at noon contrasts strongly with the grey of the platform of older rock.... These huge isolated cones are among the most striking memorials of denudation anywhere to be seen in the British Isles. Quinag, Canisp, Suilven, Coulmore, and the hills of Coygoch, Dundonald, Loch Maree, and Torridon are merely detached patches of a formation not less than seven thousand or eight thousand feet thick, which once spread over the northwest of Scotland. The spaces between them were once occupied by the same dull red sandstone; the horizontal stratification of one hill, indeed, is plainly continuous with that of the others, though deep and wide valleys, or miles of low moorland, may now lie between. While the valleys have been worn down through the sandstone, these strange pyramidal mountains that form so singular a feature in the landscapes of the northwest highlands have been left standing, like lonely sea-stacks, as monuments of long ages of waste."[31]
Again, the vast table-lands of the Colorado region illustrate on a truly magnificent scale, to which there is no parallel in the Old World, the effects of atmospheric erosion on undisturbed and nearly level strata. Here we find valleys and river gorges deeper and longer than any others in the world; great winding lines of escarpment, like ranges of sea cliffs; terraced slopes rising at various levels; huge buttresses and solitary monuments, standing like islands out of the plains; and lastly, great mountain masses carved out into the most striking and picturesque shapes, yet with their lines of "bedding" clearly marked out.
On the other hand, where, as is almost always the case in mountain-ranges, the stratified rocks have been folded, crumpled, twisted, and fractured by great "faults," we find a very different result. In these cases the rocks have generally been very much altered by the action of heat. For here we find crystalline schists, gneiss, granite, and other rocks in the formation of which heat has played an important part; and very often the igneous rocks have forced their way through those of sedimentary origin and altered them into what are called metamorphic rocks (see chapter v., page [156]). Thus they have lost much of their original character and structure.
The repeated uplifts and subsidences of the earth's crust, by which the continents of the world have been raised up out of the sea to form dry land, have, broadly speaking, thrown the rocky strata into a series of wave-like undulations. In some extensive regions these undulations are so broad and low that the curvature is quite imperceptible, and the strata appear to lie in horizontal layers, or to slope very slightly in a certain direction. This is, in a general way, the position of the strata of which plains and plateaux are composed.
But in the longer and comparatively narrow mountain regions that traverse each of the great continents, forming, as it were, backbones to them, the undulations are very much more frequent, narrower, and higher. Sometimes the rocks have been thrown into huge open waves, or the folds are closely crowded together, so that the strata stand on their ends, or are even completely overturned, and thus their proper order of succession is reversed, and the older ones actually lie on the top of the newer ones.
As we approach a great mountain-chain we observe many minor ridges and smaller chains running roughly parallel with it, and, as it were, foreshadowing the great folds met with in the centre of the chain and among its highest peaks. These small folds become sharper and closer the nearer we get to the main chain, and evidently were formed by the same movements that uplifted the higher ranges beyond; but the force was not so great. Thus we find the great Alpine chain flanked to the north by the smaller ranges of the Jura Mountains; and on the south, side of the Himalayas we find similar smaller ranges of hills.
Ruskin thus describes his impression of the Jura ranges, which he very aptly compares with a swell on the sea far away from a storm, the storm being represented by the wild sea of Alpine mountains:—
"Among the hours of his life to which the writer looks back with peculiar gratitude, as having been marked with more than ordinary fulness of joy or clearness of teaching, is one passed, now some years ago, near time of sunset, among the masses of pine forest which skirt the course of the Ain, above the village of Champagnole, in the Jura. It is a spot which has all the solemnity, with none of the savageness, of the Alps; where there is a sense of a great power beginning to be manifested in the earth, and of a deep and majestic concord in the rise of the long low lines of piny hills,—the first utterance of those mighty mountain symphonies, soon to be more loudly lifted and wildly broken along the battlements of the Alps. But their strength is as yet restrained; and the far-reaching ridges of pastoral mountain succeed each other, like the long and sighing swell which moves over quiet waters from some far-off stormy sea.
"And there is a deep tenderness pervading that vast monotony. The destructive forces and the stern expression of the central ranges are alike withdrawn. No frost-ploughed, dust-encumbered paths of ancient glacier fret the soft Jura pastures; no splintered heaps of ruin break the fair ranks of her forests; no pale, defiled, or furious rivers rend their rude and changeful ways among her rocks. Patiently, eddy by eddy, the clear green streams wind along their well-known beds; and under the dark quietness of the undisturbed pines there spring up, year by year, such company of joyful flowers as I know not the like among all the blessings of the earth."
Long faults, or fractures, where the strata have been first bent and then broken, and afterwards have been forced up or have slid down hundreds or even thousands of feet, are very numerous in mountain-ranges; and by suddenly bringing quite a different set of rocks to the surface, these faults cause considerable difficulty to the geologist, as he goes over the ground and endeavours to trace the positions of the different rocks.