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. [Illustration: FIG. 74.] [Illustration: FIG. 75.] Sec. 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. Sec. 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. [Illustration: Fig. 77.]