highly inclined, than from those whose stratification is more nearly or quite level, and the volume generally will be greater of the mass that shall be capable of dislodgment at once. Again, whether, like the Rosberg, it shall slip and launch en masse upon a greasy bed, or fall a dislocated chaos, like the great fall of rock at Plürs, (Lyell, 'Geol.,' p. 704,) will much depend upon the direction of the planes of stratification at the place, with regard to the line of the wave-path.
The only instance of a fall of rock observed by me, in which there was actual fracture, through any considerable thickness, of previously sound and unbroken rock, was in the "aiguille," at the valley to the rear of Padula, where it was broken (like a wall at its base) by transverse action.
This class of secondary eflfect, is therefore capable of producing its largest developments, in either of two modes. A shock, itself perhaps very moderate, may induce motion in a huge mass, which, like the Rosberg, may slide almost as one immense block, and considerable lateral transfer of material, be thus produced without great change of elevation, or with it. And if the slipped mass, be of clay, &c., by resolution of intestine forces, the pressures at the toe of the talus, may produce elevations in parts of the mass, or in other masses of clay, i.e., such phenomena as those recorded by Dolomieu having occurred at Terra Nuova, and Cossolito, &c, in Calabria in 1783.
Or, a shock perhaps equally moderate, passing through an extremely elevated and steep country, of lofty peaks and deep gorges, whose higher regions are bare surfaces of shattery rock, may bring down by the shake, millions of
