Sec. 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. Sec. 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. Sec. 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