Page:Great Neapolitan Earthquake of 1857.djvu/320

262 in Fig. 137, which dip pretty sharply to the south. I find upon inquiry here that Petina, which is just five



Italian miles S. W. of Auletta, and about six from Pertosa, has nevertheless suffered absolutely nothing, although these latter towns are in great part prostrated.

The immunity of Castelluccio from injury arose, as I before remarked, from the long dimension of its well-buttressed knoll being opposed to the line of shock, as well as to the barrier interposed between it and any shock coming from the eastward, b the mass of vertical breccia beds to the east of the town.

Petina has owed its immunity, first to the peculiarly strong form of the terrace upon which it is perched to resist any vibration in the mass itself, secondly, to the fact that from where I stand at Auletta Bridge, there is about 1,000 feet of piled-up limestone beds between me and Petina, so that any shock emergent at a steep angle, here or further eastward, must have passed up transversely through all these successive plates of variable hardness, and none in absolute contact with each other, and so the vis vivâ of the shock be enormously reduced before reaching the elevation of the