Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/424

Rh material, or those on the solid rocks on hill tops, suffered most; and their discussions evince much obscurity of thought, having no guiding principle.

We have in this earthquake, towns such as Saponara and Viggiano, situated upon solid limestone totally prostrated; and we have others, such as Montemurro, to a great extent based upon loose clays, also totally levelled. We have examples of almost complete immunity, in places posited in plains of deep clays, as that of Viscolione, and in places on solid limestone like Castelluccio, or perched on mountain tops like Petina.

Were the whole of the facts of Part II. discussed with regard to this question, it would be found, that more places were destroyed upon the rock, than upon loose clay or other such foundations, and more upon hills than upon plains; but this would not conduct us to the whole truth, because in all South Italy, there are a great many more places upon rock and upon hills, than upon clays and low plains.

Whether it be rock or clay, has, in reality, but a secondary influence. The transit rate, and to a greater or less extent, the velocity and amplitude of the wave will be different; the velocity greater and the amplitude less in the rock, and vice versâ in the clays or gravels: but the great differences will be found to arise, not from any molecular properties in the substances, beneath the respective places shaken, but to be caused by the elevation, contour, and form, &c., of the masses, upon which the places are built; and upon their positions in relation to the physical features and deposition of the formations, intervening between them and the focal point.

If a town stand upon a lofty, isolated, rocky eminence,