RESULTING FORMS:—THIRDLY, PRECIPICES.
§ 1. The reader was, perhaps, surprised by the smallness of the number to which our foregoing analysis reduced Alpine summits bearing an ascertainedly peaked or pyramidal form. He might not be less so if I were to number the very few occasions on which I have seen a true precipice of any considerable height. I mean by a true precipice, one by which a plumb-line will swing clear, or without touching the face of it, if suspended from a point a foot or two beyond the brow. Not only are perfect precipices of this kind very rare, but even imperfect precipices, which often produce upon the eye as majestic an impression as if they were vertical, are nearly always curiously low in proportion to the general mass of the hills to which they belong. They are for the most part small steps or rents in large surfaces of mountain, and mingled by Nature among her softer forms, as cautiously and sparingly as the utmost exertion of his voice is, by a great speaker, with his tones of gentleness.
| Fig. 73. |
§ 2. Precipices, in the large plurality of cases, consist of the edge of a bed of rock, sharply fractured, in the manner already explained in Chap. XII., and are represented, in their connection with aiguilles and crests, by c, in [Fig. 42], [p. 195]. When the bed of rock slopes backwards from the edge, as a, [Fig. 73], a condition of precipice is obtained more or less peaked, very safe, and very grand.[80] When the beds are horizontal, b, the precipice is steeper, more dangerous, but much less impressive. When the beds slope towards the precipice, the front of it overhangs, and the noblest effect is obtained which is possible in mountain forms of this kind.
§ 3. Singularly enough, the type b is in actual nature nearly always the most dangerous of the three, and c the safest, for horizontal beds are usually of the softest rocks, and their cliffs are caused by some violent agency in constant operation, as chalk cliffs by the wearing power of the sea, so that such rocks are continually falling, in one place or another. The form a may also be assumed by very soft rocks. But c cannot exist at all on the large scale, unless it is built of good materials, and it will then frequently stay in its fixed frown for ages.
§ 4. It occasionally happens that a precipice is formed among the higher crests by the sides of vertical beds of slaty crystallines. Such rocks are rare, and never very high, but always beautiful in their smoothness of surface and general trenchant and firm expression. One of the most interesting I know is that of the summit of the Breven, on the north of the valley of Chamouni. The mountain is formed by vertical sheets of slaty crystallines, rather soft at the bottom, and getting harder and harder towards the top, until at the very summit it is hard and compact as the granite of Waterloo Bridge, though much finer in the grain, and breaking into perpendicular faces of rock so perfectly cut as to feel smooth to the hand. [Fig. 4], [p. 107], represents, of the real size, a bit which I broke from the edge of the cliff, the shaded part underneath being the surface which forms the precipice. The plumb-line from the brow of this cliff hangs clear 124 English feet; it is then caught by a ledge about three feet wide, from which another precipice falls to about twice the height of the first; but I had not line enough to measure it with from the top, and could not get down to the ledge. When I say the line hangs clear, I mean when once it is off the actual brow of the cliff, which is a little rounded for about fourteen or fifteen feet, from a to b, in the section, [Fig. 75]. Then the rock recedes in an almost unbroken concave sweep, detaching itself from the plumb-line about two feet at the point c (the lateral dimensions are exaggerated to show the curve), and approaching it again at the ledge d, which is 124 feet below a. The plumb-line, fortunately, can be seen throughout its whole extent from a sharp bastion of the precipice farther on, for the face of the cliff runs, in horizontal plan, very nearly to the magnetic north and south, as shown in [Fig. 74], the plumb-line swinging at a, and seen from the advanced point P. It would give a similar result at any other part of the cliff face, but may be most conveniently cast from the point a, a little below, and to the north of the summit.
| Fig. 74. | Fig. 75. |
§ 5. But although the other divisions of this precipice, below the ledge which stops the plummet, give it altogether a height of about five hundred feet,[81] the whole looks a mere step on the huge slope of the Breven; and it only deserves mention among Alpine cliffs as one of singular beauty and decision, yet perfectly approachable and examinable even by the worst climbers; which is very rarely the case with cliffs of the same boldness. I suppose that this is the reason for its having been often stated in scientific works that no cliff could be found in the Alps from which a plumb-line would swing two hundred feet. This can possibly be true (and even with this limitation I doubt it) of cliffs conveniently approachable by experimental philosophers. For, indeed, one way or another, it is curious how Nature fences out, as it were, the brows of her boldest precipices. Wherever a plumb-line will swing, the precipice is, almost without exception, of the type c, in [Fig. 73], the brow of it rounding towards the edge for, perhaps, fifty or a hundred yards above, rendering it unsafe in the highest degree for any inexperienced person to attempt approach. But it is often possible to ascertain from a distance, if the cliff can be got relieved against the sky, the approximate degree of its precipitousness.
§ 6. It may, I think, be assumed, almost with certainty, that whenever a precipice is very bold and very high, it is formed by beds more or less approaching horizontally, out of which it has been cut, like the side of a haystack from which part has been removed. The wonderfulness of this operation I have before insisted upon; here we have to examine the best examples of it.
As, in forms of central rock, the Aiguilles of Chamouni, so in notableness of lateral precipice, the Matterhorn, or Mont Cervin, stands, on the whole, unrivalled among the Alps, being terminated, on two of its sides, by precipices which produce on the imagination nearly the effect of verticality. There is, however, only one point at which they reach anything approaching such a condition; and that point is wholly inaccessible either from below or above, but sufficiently measurable by a series of observations.