The second reason appears to be that rocks composed in this manner are capable of more interesting variety in form than any others; and as they were continually to be exposed to sight in the high ranges, they were so prepared as to be always as interesting and beautiful as possible.
§ 12. These crystalline or spotted rocks we must again separate into two great classes, according to the arrangement, in them, of the particles of a substance called mica. It is not And divisible into two classes, Compact Crystallines and Slaty Crystallines. present in all of them; but when it occurs, it is usually in large quantities, and a notable source of character. It varies in color, occurring white, brown, green, red, and black; and in aspect, from shining plates to small dark grains, even these grains being seen, under a magnifier, to be composed of little plates, like pieces of exceedingly thin glass; but with this great difference from glass, that, whether large or small, the plates will not easily break across, but are elastic, and capable of being bent into a considerable curve; only if pressed with a knife upon the edge, they will separate into any number of thinner plates, more and more elastic and flexible according to their thinness, and these again into others still finer; there seeming to be no limit to the possible subdivision but the coarseness of the instrument employed.
| Fig. 3. |
§ 13. Now, when these crystals or grains, represented by the black spots and lines in [Fig. 3], lie as they do at a in that figure, in all directions, cast hither and thither among the other materials of the stone,—sometimes on their faces, sometimes on their sides, sometimes on their edges,—they give the rock an irregularly granulated appearance and structure, so that it will break with equal ease in any direction; but if these crystals lie all one way, with their sides parallel, as at b, they give the rock a striped or slaty look, and it will most readily break in the direction in which they lie, separating itself into folia or plates, more or less distinctly according to the quantity of mica in its mass. In the example [Fig. 4], a piece of rock from the top of Mont Breven, there are very few of them, and the material with which they are surrounded is so hard and compact that the whole mass breaks irregularly, like a solid flint, beneath the hammer; but the plates of mica nevertheless influence the fracture on a large scale, and occasion, as we shall see hereafter, the peculiar form of the precipice at the summit of the mountain.[43]
The rocks which are destitute of mica, or in which the mica lies irregularly, or in which it is altogether absent, I shall call Compact Crystallines. The rocks in which the mica lies regularly I shall call Slaty Crystallines.
§ 14. 1st. Compact Crystallines.—Under this head are embraced Compact Crystallines. the large group of the granites, syenites, and porphyries,—rocks which all agree in the following particulars:—
| Fig. 4. |
A. Variety of color.—The method of their composition out of different substances necessitates their being all more or less spotted or dashed with various colors; there being generally a Their first characteristic. Speckledness. prevalent ground color, with other subordinate hues broken over it, forming, for the most part, tones of silver grey, of warm but subdued red, or purple. Now, there is in this a very marvellous provision for the beauty of the central ranges. Other rocks, placed lower among the hills, receive color upon their surfaces from all kinds of minute vegetation; but these higher and more exposed rocks are liable to be in many parts barren; and the wild forms into which they are thrown necessitate their being often freshly broken, so as to bring their pure color, untempered in anywise, frankly into sight. Hence it is appointed that this color shall not be raw or monotonous, but composed—as all beautiful color must be composed—by mingling of many hues in one. Not that there is any aim at attractive beauty in these rocks; they are intended to constitute solemn and desolate scenes; and there is nothing delicately or variously disposed in their colors. Such beauty would have been inconsistent with their expression of power and terror, and it is reserved for the marbles and other rocks of inferior office. But their color is grave and perfect; closely resembling, in many cases, the sort of hue reached by cross-chequering in the ground of fourteenth-century manuscripts, and peculiarly calculated for distant effects of light; being, for the most part, slightly warm in tone, so as to receive with full advantage the red and orange rays of sunlight. This warmth is almost always farther aided by a glowing orange color, derived from the decomposition of the iron which, though in small quantity, usually is an essential element in them: the orange hue forms itself in unequal veins and spots upon the surfaces which have been long exposed, more or less darkening them; and a very minute black lichen,—so minute as to look almost like spots of dark paint,—a little opposed and warmed by the golden Lichen geographicus, still farther subdues the paler hues of the highest granite rocks. Now, when a surface of this kind is removed to a distance of four or five miles, and seen under warm light through soft air, the orange becomes russet, more or less inclining to pure red, according to the power of the rays: but the black of the lichen becomes pure dark blue; and the result of their combination is that peculiar reddish purple which is so strikingly the characteristic of the rocks of the higher Alps. Most of the travellers who have seen the Valley of Chamouni carry away a strong impression that its upper precipices are of red rock. But they are, without exception, of a whitish grey, toned and raised by this united operation of the iron, the lichen, and the light.
§ 15. I have never had an opportunity of studying the effects of these tones upon rocks of porphyry; but the beautiful color of that rock in its interior substance has rendered it one of the favorite materials of the architects of all ages, in their most costly work. Not that all porphyry is purple; there are green and white porphyries, as there are yellow and white roses; but the first idea of a porphyry rock is that it shall be purple,—just as the first idea of a rose is that it shall be red. The purple inclines always towards russet[44] rather than blue, and is subdued by small spots of grey or white. This speckled character, common to all the crystalline rocks, fits them, in art, for large and majestic work; it unfits them for delicate sculpture; and their second universal characteristic is altogether in harmony with this consequence of their first.