Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/343

278 the wave-paths, radiating from the seismic vertical, here crossed somewhat obliquely, the deep and continuous valley, and flanking ranges of the river course, and hence the wave here suffered a partial and sudden arrest.

These remarks will I hope, be sufficient to make clear, the great modifying causes (so far as surface is concerned), that have determined the forms of these isoseismals, and limited the areas of equal destructive effect, of this earthquake. The same principles of explanation will be found to apply to the second isoseismal (— ··· — ··· -). The great east and west chain of the Apennine, stretching across from Baronissi to Spinazzola, and at a direct transverse distance from the seismal vertical, of only about ten geographical miles, to the very axial line, opposed itself with all its parallel ranges, transversely to the propagation of the wave, to the north, and north by west; while the causes operative, in the meizoseismal and first isoseismal areas, as already described, were also so here, in extending the propagation of the wave towards the south, south-east, and east.

To the extreme S.E. end of the second isoseismal, the flattening of the curve, and narrowing of the band of country, between the first and second curves; is ascribable, to the wave having there reached the low-lying clays and other discontinuous littoral deposits, that skirt the shores of the Gulf of Tarentum. To a like reason is to be attributed, that its progress towards the south-west extended no further than the seaward slopes, of the great masses of the Monte Alburno range, leaving the deep clay plains of Pæstum, from near Salerno to Agropoli, almost untouched.

Had I been able to extend my survey, to the whole of the country between the second and third isoseismals,