§ 11. Not so the mountain drift-cloud, which is as peculiar as it is majestic. The Plates 70 and 71 show, as well as I can express, two successive phases of it on a mountain crest; (in this instance the great limestone ridge above St. Michel, in Savoy.) But what colossal proportions this noble cloud assumes may be best gathered from the rude sketch, Fig. 87, in which I have simply put firm black ink over the actual pencil lines made at the moment, giving the form of a single wreath of the drift-cloud, stretching about five miles in a direct line from the summit of one of the Alps of the Val d'Aosta, as seen from the plain of Turin. It has a grand volcanic look, but I believe its aspect of rising from the peak to be almost, if not altogether, deceptive; and that the apparently gigantic column is a nearly horizontal stream of lee-side cloud, tapered into the distance by perspective, and thus rising at its apparently lowest but in reality most distant point, from the mountain summit whose shade calls it into being out of the clear winds. Whether this be so or not, the apparent origin of the cloud on the peak, and radiation from it, distinguish it from the drift-cloud of level country, which arranges itself at the horizon in broken masses, such as Fig. 89, showing no point of origin; and I do not know how far they are vertical cliffs or horizontally extended fields. They are apt to be very precipitous in aspect, breaking into fragments with an apparently concentric motion, as in the figure; but of this motion also--whether vertical or horizontal--I can say nothing positive. § 12. The absolute scale of such clouds may be seen, or at least demonstrated, more clearly in Fig. 88, which is a rough note of an effect of sky behind the tower of Berne Cathedral. It was made from the mound beside the railroad bridge. The Cathedral tower is half-a-mile distant. The great Eiger of Grindelwald is seen just on the right of it. This mountain is distant from the tower thirty-four miles as the crow flies, and ten thousand feet above it in height. The drift-cloud behind it, therefore, being in full light, and showing no overhanging surfaces, must rise at least twenty thousand feet into the air.