Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/149



and sharp ascent, leads up to the monastery from the margin of the lake beneath (Photog. No. 327). As I approach it, the path is, I find, blocked by a huge fallen fragment of lava, dislodged by the shock from the cliff above. It has fallen in a direction 67° E. of north, towards the S.W. A fine young walnut tree of two boles, each of 14 ins. diameter, lies crushed and mangled beneath the fallen mass. (Sketch No. 326, Coll. Roy. Soc.)

The block is 13 feet long, 11 feet wide, and 8 feet thick, mean dimensions: it has fallen from a height, at $$\mathrm A$$, of 43 feet, pitched upon its lower end at $$\mathrm K$$, 14 feet horizontally from the point of displacement, and then falling over forward upon the steep slope, has overwhelmed the tree and been arrested by its timbers. If we assume the angle of emergence at Monticchio, to be about the mean of those given by Melfi, Barielle, and Atella=15°, we obtain the following as the velocity of the wave of shock here.

Bearing in mind that the fissures in the building (as immediately after given) prove that the return stroke from the mountain which projected the rock was made with a