Page:Great Neapolitan Earthquake of 1857.djvu/323

Rh depression of the subjacent formations. For the great direction in length, of the fissures, is not far from that of the wave-path here, while it is everywhere but little removed from one, transverse to a line up and down the slope of the hills.

The people generally stated, that these fissures were at first, from one to two palms wide, at the widest, and that in steep places, one of the lips was about a palm above the other, and that in one place, the depth had been probed with a rod to nearly thirty palms. The fissures evidently had in no case run down plumb into the soil, but sloped in the same direction, but with a less angle to the vertical than the hill side on which it was found.

There is hence nothing very surprising in their occurrence. They are all in deep soft diluvial clays, of great specific gravity, very fine grained, and almost free from gravel and stones—a tenacious clay loam, that when wetted gets at once into a sticky paste, and soon runs into a greasy cream, so that a very small declivity and moisture alone, produce frequent land slips. Thus on the road leading from Auletta, along the slope of the hill, towards Villa Carusso, (which is also that to Salvitella and Vietri,) on the N. W. side of the valley, I observed a place where a slip had occurred, upon a bed of not above 12° or 15° slope, which a year or two since had carried away the whole road (here on side cutting), and lowered its surface about 4 feet, for some 400 feet in length, carrying with it the telegraph poles, still standing fast in the soil.

But a small effort of vibratory movement, therefore, must be sufficient partially to dislodge masses of such material, on much steeper slopes. The average slope of the rock, beneath the soil of the great fissure here, cannot