Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/347

282 The abstract direction of the axial line is marked on Map A (original) by a red line; the wave-paths, as ascertained for Salerno, La Cava, Amalfi, and other places, to the south of the range, and also those for Naples, Capua, Ottajano, and others north of it, are marked, and the direction of transit shown by "arrow heads." And on Maps A and B, the probable forms of the isoseismals, of this separate reflected and refracted system, are marked in thus ( — ), that to the south of the range, which falls almost wholly in the sea, in the Gulf of Salerno, being only inferential.

The whole of the St. Angelo range of limestone mountains, as stated in Part II., is highly metamorphic, forming, as it does, the southern lip of the vast volcanic basin of the Vesuvian area. The wave from the focus, to near Salerno, passed through Apennine, and still newer, limestones, and calcareous breccias and loose deposits. Upon impinging on this mountain range, it reached at once, a continuous wall of rocks, of variable but greatly higher elasticity, and superior density; and at an angle of incidence (horizontally) of 56° to 59°, a reflected wave was produced.

The observed wave-paths at Amalfi and Atrani, &c., prove that this was so, the direction being N. 133° west, which gives the angle of their wave-paths, with the perpendicular to the mountain axis,= 59°, or the angles of incidence and of reflection equal. The wave, no doubt at a low level, in the base of the chain, passed through, suffering refraction twice, and crossed the Bay of Naples, beneath the sea, and was observed, as to direction of its path, at Pausillipo, N. 38° west. The directions of the wave-paths at Salerno and at Eboli, N. 66° to 67° west, which, as already stated,