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CHAPTER XV.

RESULTING FORMS :-SECONDLY, CRESTS.

§ 1. BETWEEN the aiguilles, or other conditions of central peak, and the hills which are clearly formed, as explained in Chap. XII. § 11, by the mere breaking of the edges of solid beds of coherent rock, there occurs almost always a condition of mountain summit, intermediate in aspect, as in position. The aiguille may generally be represented by the type a, Fig. 42; the solid and simple beds of rock by the type c. The condition b, clearly intermediate between the two, is, on the whole, the most graceful and perfect in which mountain masses occur. It seems to have attracted more of the attention of the poets than either of the others; and the ordinary word, crest, which

FIG. 42.

we carelessly use in speaking of mountain summits, as if it meant little more than "edge" or "ridge," has a peculiar force and propriety when applied to ranges of cliff whose contours correspond thus closely to the principal lines of the crest of a Greek helmet.

§ 2. There is another resemblance which they can hardly fail to suggest when at all irregular in form,-that of a wave about to break. Byron uses the image definitely of Soracte; and, in a less clear way, it seems to present itself occasionally to all minds, there being a general tendency to give or accept accounts of mountain form under the image of waves; and to

speak of a hilly country, seen from above, as looking like a "sea of mountains.

Such expressions, vaguely used, do not, I think, generally imply much more than that the ground is waved or undulated into bold masses. But if we give prolonged attention to the mountains of the group b we shall gradually begin to feel that more profound truth is couched under this mode of speaking, and that there is indeed an appearance of action and united movement in these crested masses, nearly resembling that of sea waves; that they seem not to be heaped up, but to leap or toss themselves up; and in doing so, to wreathe and twist their summits into the most fantastic, yet harmonious, curves, gov

FIG. 43.

erned by some grand under-sweep like that of a tide, running through the whole body of the mountain chain.

For instance, in Fig. 43, which gives, rudely, the leading lines of the junction of the "Aiguille pourri "** (Chamouni) with the Aiguilles Rouges, the reader cannot, I think, but feel that there is something which binds the mountains togethersome common influence at their heart which they cannot resist : and that, however they may be broken or disordered, there is as true unity among them as in the sweep of a wild wave, governed, through all its foaming ridges, by constant laws of weight and motion.

* So called from the mouldering nature of its rocks. They are slaty crystallines, but unusually fragile.

§ 3. How far this apparent unity is the result of elevatory force in mountain, and how far of the sculptural force of water

FIG. 44.

upon the mountain, is the question we have mainly to deal with in the present chapter.

I

But first look back to Fig. 7, of Plate 8, Vol. III., there given as the typical representation of the ruling forces of growth in a leaf. Take away the extreme portion of the curve on the left, and any segment of the leaf remaining, terminated by one of its ribs, as a or b, Fig. 44, will be equally a typical contour of a common crested mountain. If the reader will merely turn Plate 8 so as to look at the figure upright, with its stalk downwards, he will see that it is also the base of the honeysuckle ornament of the Greeks. I may anticipate what we shall have to note with respect to vegetation so far as to tell him that it is also the base of form

FIG. 45.

in all timber trees.

a

b

§ 4. There seems something, therefore, in this contour which makes its production one of the principal aims of Nature in all her compositions. The cause of this appears to be, that as the cinq-foil is the simplest expression of proportion, this is the simplest expression of opposition, in unequal curved. lines. If we take any lines, a x and e g, Fig. 45, both of varied curvature (not segments of circles), and one shorter than the other, and join them together so as to form one line, as b x, x g, we shall have one of the common lines of beauty; if we join them at an angle, as

FIG. 46.

cx, xy, we shall have the common crest, which is in fact merely a jointed line of beauty. If we join them as at a, Fig. 46, they form a line at once monotonous and cramped, and the jointed condition of this same line, b, is hardly less so. It is easily proved, therefore, that the junction of lines c x, x y, is the simplest and most graceful mode of opposition; and easily observed that in branches of trees, wings of birds, and other more or less regular organizations, such groups of line are continually made to govern the contours. But it is not so easily seen why or how this form should be impressed upon irregular heaps of mountain.

§ 5. If a bed of coherent rock be raised, in the manner described in Chap. XIII., so as to form a broken precipice with

a

FIG. 47.

its edge, and a long slope with its surface, as at a, Fig. 47 (and in this way nearly all hills are raised), the top of the precipice has usually a tendency to crumble down, and, in process of time, to form a heap of advanced ruins at its foot. On the other side, the back or slope of the hill does not crumble down, but is gradually worn away by the streams; and as these are always more considerable, both in velocity and weight, at the bottom of the slope than the top, the ground is faster worn away at the bottom, and the straight slope is cut to a curve of continually increasing steepness. Fig. 47 b represents the contour to which the hill a would thus be brought in process time; the dotted line indicating its original form. The result, it will be seen, is a crest.*

* The materials removed from the slope are spread over the plain or valley below. A nearly equal quantity is supposed to be removed from the other side; but besides this removed mass, the materials crumble heavily from above, and form the concave curve.

§ 6. But crests of this uniform substance and continuous outline occur only among hills composed of the softest coherent rocks, and seldom attain any elevation such as to make them important or impressive. The notable crests are composed of the hard coherents or slaty crystallines, and then the contour of

FIG. 48.

the crests depends mainly on the question whether, in the original mass of it, the beds lie as at a or as at b, Fig. 48. If they lie as at a, then the resultant crest will have the general appearance seen at c; the edges of the beds getting separated and serrated by the weather. If the beds lie as at b, the resultant crest will be of such a contour as that at d.

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