Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/328

Rh refracted, and also partially reflected; and the refraction at different points may possibly be in contrary directions; hence great complication in the wave issuing along the slope, and loss of its energy.

When stratified formations repose conformably, upon the ingoing flank of a mountain range, (as to the right-hand of Fig. 343,) and the angle of emergence of the wave at the base of the range is such, as to pass it nearly "end on" into such strata, (of newer beds for example reposing on older, and having no hold upon them); then the whole of the wave that enters these beds, will pass off at the free outlying surfaces of their upper extremities and be then extinguished;

the wave thus "breaking" upon the slope of the central formations, like a ripple upon a sea-beach; while such portion of it as passes deeper, and through the innermost axial formation, will emerge at the outgoing flank, (to the left,) after having sustained all the losses of vis vivâ and volume already described, by change of medium, refraction, and reflection.

Again, when loose and incoherent masses, (such as the gravel and clay deposits in valleys and river courses,) repose upon the gentler slopes of the bases, of the lower ranges, the wave entering such at a small angle of emergence, will be almost completely extinguished, by compression, and change