Sec. 17. The more I examined the range of the aiguilles the more I was struck by this curved cleavage as their principal character. It is quite true that they have other straighter cleavages (noticed in the Appendix, as the investigation of them would be tiresome to the general reader); but it is this to which they owe the whole picturesqueness of their contours; curved as it is, not simply, but often into the most strange shell-like undulations, as will be understood by a glance at Fig. 37, which shows the mere _governing_ lines at the base of this Aiguille Blaitiere, seen, with its spur, from a station some quarter of a mile nearer it, and more to the east than that chosen in Plate +31+. These leading lines are rarely well shown in fine weather, the important contour from _a_ downwards being hardly relieved clearly from the precipice beyond (_b_), unless a cloud intervenes, as it did when I made this memorandum; while, again, the leading lines of the Aiguille du Plan, as seen from the foot of it, close to the rocks, are as at Fig. 38, the generally pyramidal outline being nearly similar to that of Blaitiere, and a spur being thrown out to the right, under _a_, composed in exactly the same manner of curved folia of rock laid one against the other. The hollow in the heart of the aiguille is as smooth and sweeping in curve as the cavity of a vast bivalve shell. [Illustration: FIG. 38.] Sec. 18. I call these the governing or leading lines, not because they are the first which strike the eye, but because, like those of the grain of the wood in a tree-trunk, they rule the swell and fall and change of all the mass. In Nature, or in a photograph, a careless observer will by no means be struck by them, any more than he would by the curves of the tree; and an ordinary artist would draw rather the cragginess and granulation of the surfaces, just as he would rather draw the bark and moss of the trunk. Nor can any one be more steadfastly adverse than I to every substitution of anatomical knowledge for outward and apparent fact; but so it is, that as an artist increases in acuteness of perception, the facts which _become_ outward and apparent to him are those which bear upon the growth or make of the thing. And, just as in looking at any woodcut of trees after Titian or Albert Durer, as compared with a modern water-color sketch, we shall always be struck by the writhing and rounding of the tree trunks in the one, and the stiffness, and merely blotted or granulated surfaces of the other; so, in looking at these rocks, the keenness of the artist's eye may almost precisely be tested by the degree in which he perceives the curves that give them their strength and grace, and in harmony with which the flakes of granite are bound together, like the bones of the jaw of a saurian. Thus the ten years of study which I have given to these mountains since I described them in the first volume as "traversed sometimes by graceful