Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/146

Rh following any one of them up to the head, it is found that several minor rain torrents from the sides of the cone have coalesced, and that after having run upon the surface with a gradually lowering bed for some distance, they suddenly plunge down (Fig. 324) over a vertical wall of tufa, forming a cascade of from 2 or 3, to 20 or 30 feet in height (Fig. 325), but which only runs during rains. Here the cutting back of the tufa proceeds at a visible rate, and what is very remarkable, although the total depth of the ravine slowly decreases, as it is eaten out, upwards towards the cone, the abrupt perpendicularity of its head, over which the waters shoot or trickle, never changes, or becomes levelled to a talus.

Here is the point at which any one of these ravines can first be crossed; some hundreds of which intersect the flanks and plains around the great cone,—if cone, the vast irregular mass of Vulture, may be called—and form the feeders to the upper forks of the Ofanto, which drains the whole region.

The cone itself, upon its S. E. side especially, presents in its outlines and surface the most striking characteristics of enormous erosion by rain (Sketch, Fig. 324). Not a vestige of lava or hard rock is visible here—all is a rounded, furrowed, and worn mass of consolidated tufa.

As we leave the slopes that blend the plain with the mountain, and ascending some two miles more, reach its S.W. shoulder, isolated blocks of lava crop out here and there, and in some places are exposed in mass in the ravines. Thence the way lies wholly through the forest, El Bosco della Pietra, or De Bucito, for about two miles more.

VOL. IIH