: 1st. The path of the wave—Subnormal.

2nd. The direction of transit—the fissures being occasionally most open at the end first reached by the wave, and the transit always from the end that dips below the horizon.

3rd. The angle of emergence of the wave with the horizon being equal to the angle made by the main fissures (or those transverse to the wave-path) with the vertical.

4th. The velocity of the wave motion may, under favourable circumstances, be inferred from that impressed upon detached and fallen masses.

Abundant examples will occur, in the second part of this Report, of these subnormal waves, and of their effects.