[66] So called from the mouldering nature of its rocks. They are slaty crystallines, but unusually fragile.
[67] 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.
[68] The lines are a little too straight in their continuations, the engraver having cut some of the curvature out of their thickness, thinking I had drawn them too coarsely. But I have chosen this coarsely lined example, and others like it, following, because I wish to accustom the reader to distinguish between the mere fineness of instrument in the artist's hand, and the precision of the line he draws. Give Titian a blunt pen, and still Titian's line will be a noble one: a tyro, with a pen well mended, may draw more neatly; but his lines ought to be discerned from Titian's, if we understand drawing. Every line in this woodcut of Durer's is refined; and that in the noblest sense. Whether broad or fine does not matter, the lines are right; and the most delicate false line is evermore to be despised, in presence of the coarsest faithful one.
[69] Not absolutely on the meeting of the curves in one point, but on their radiating with some harmonious succession of difference in direction. The difference between lines which are in true harmony of radiation, and lines which are not, can, in complicated masses, only be detected by a trained eye; yet it is often the chief difference between good and bad drawing. A cluster of six or seven black plumes forming the wing of one of the cherubs in Titian's Assumption, at Venice, has a freedom and force about it in the painting which no copyist or engraver has ever yet rendered, though it depends merely on the subtlety of the curves, not on the color.
[70] "Out of perspective," I should have said: but it will show what I mean.
[71] Nor did any nearer observations ever induce me to form any contrary opinion. It is not easy to get any consistent series of measurements of the slope of these gneiss beds; for, although parallel on the great scale, they admit many varieties of dip in minor projections. But all my notes unite, whether at the bottom or top of the great slope of the Montanvert and La Côte, in giving an angle of from 60° to 80° with the horizon; the consistent angle being about 75°. I cannot be mistaken in the measurements themselves, however inconclusive observations on minor portions of rock may be; for I never mark an angle unless enough of the upper or lower surface of the beds be smoothly exposed to admit of my pole being adjusted to it by the spirit-level. The pole then indicates the strike of the beds, and a quadrant with a plumb-line their dip; to all intents and purposes accurately. There is a curious distortion of the beds in the ravine between the Glacier des Bois and foot of the Montanvert, near the ice, about a thousand feet above the valley; the beds there seem to bend suddenly back under the glacier, and in some places to be quite vertical. On the opposite side of the glacier, below the Chapeau, the dip of the limestone under the gneiss, with the intermediate bed, seven or eight feet thick, of the grey porous rock which the French call cargneule, is highly interesting; but it is so concealed by débris and the soil of the pine forests, as to be difficult to examine to any extent. On the whole, the best position for getting the angle of the beds accurately, is the top of the Tapia, a little below the junction there of the granite and gneiss (see notice of this junction in Appendix 2); a point from which the summit of the Aiguille du Gouté bears 11° south of west, and that of the Aiguille Bouchard 17° north of east, the Aiguille Dru 5-½° or 6° north of east, the peak of it appearing behind the Petit Charmoz. The beds of gneiss emerging from the turf under the spectator's feet may be brought parallel by the eye with the slopes of the Aiguille du Gouté on one side, and the Bouchard (and base of Aiguille d'Argentière) on the other; striking as nearly as possible from summit to summit through that on which the spectator stands, or from about 10° north of east to 10° south of west, and dipping with exquisite uniformity at an angle of 74 degrees with the horizon. But what struck me as still more strange was, that from this point I could distinctly see traces of the same straight structure running through the Petit Charmoz, and the roots of the aiguilles themselves, as in [Fig. 59]; nor could I ever, in the course of countless observations, fairly determine any point where this slaty structure altogether had ceased. It seemed only to get less and less traceable towards the centre of the mass of Mont Blanc; and, from the ridge of the Aiguille Bouchard itself, at the point a in [Plate 33], whence, looking south-west, the aiguilles can be seen in the most accurate profile obtainable throughout the valley of Chamouni, I noticed a very singular parallelism even on the south-east side of the Charmoz, x y ([Fig. 60]), as if the continued influence of this cleavage were carried on from the Little Charmoz, c, d (in which, seen on the opposite side, I had traced it as in [Fig. 59]), through the central mass of rock r. In this profile, M is the Mont Blanc itself; m, the Aiguille du Midi; P, Aiguille du Plan; b, Aiguille Blaitière; C, Great Charmoz; c, Petit Charmoz; E, passage called de l'Etala.
| Fig. 59. |
| Fig. 60. |
[72] Many geologists think they are the true beds. They run across the gneissitic folia, and I hold with De Saussure, and consider them a cleavage.
[73] I tried in vain to get along the ridge of the Bouchard to this junction, the edge of the precipice between a and b ([Plate 33]) being too broken; but the point corresponds so closely to that of the junction of the gneiss and protogine on the Charmoz ridge, that, adding the evidence of the distant contour, I have no doubt as to the general relations of the rocks.