[W]hen a transverse, or, within certain limits, an oblique impulse, impinges laterally upon a continuous mountain range, two movements of vibration are communicated; the one, a wave transmitted along and in the line of the axis, the other a transverse wave, which causes the axial line to sway laterally, and transmit aquam prox. horizontal transverse wave, along from one end to the other; like thesinuous movement which travels along a long rope when, hanging suspended between two points at the same level, it is jerked suddenly at one end, transversely to its length.