degradation. At their base newer strata are seen of sand and clay,
mingled with shells; a marine deposit containing such ingredients as
would result from the decomposition of granite. The surface of this
newer (_tertiary_) formation constitutes what is called the plain of
Calabria--a platform which is flat and level, except where intersected
by narrow valleys or ravines, which rivers and torrents have excavated
sometimes to the depth of six hundred feet. The sides of these ravines
are almost perpendicular; for the superior stratum, being bound together
by the roots of trees, prevents the formation of a sloping bank. The
usual effect of the earthquake, he continues, was to disconnect all
those masses which either had not sufficient bases for their bulk, or
which was supported only by lateral adherence. Hence it follows that
throughout almost the whole length of the chain, the soil which adhered
to the granite at the base of the mountains Caulone, Esope, Sagra, and
Aspramonte, slid over the solid and steeply inclined nucleus, and
descended somewhat lower, leaving almost uninterruptedly from St. George
to beyond St. Christina, a distance of from nine to ten miles, a chasm
between the solid granitic nucleus and the sandy soil. Many lands
slipping thus were carried to a considerable distance from their former
position, so as entirely to cover others; and disputes arose as to whom
the property which had thus shifted its place should belong.

From this account of Dolomieu we might anticipate, as the result of a
continuance of such earthquakes, first, a longitudinal valley following
the line of junction of the older and newer rocks; secondly, greater
disturbance in the newer strata near the point of contact than at a
greater distance from the mountains; phenomena very common in other
parts of Italy at the junction of the Apennine and Subapennine
formations.

Mr. Mallet, in his valuable essay on the Dynamics of Earthquakes,[667]
offers the following explanation of the fact to which Dolomieu has
called attention. When a wave of elastic compression, of which he
considers the earth-wave to consist, passes abruptly from a body having
an extremely low elasticity, such as clay and gravel, into another like
granite, whose elasticity is remarkably high, it changes not only its
velocity but in part also its course, a portion being reflected and a
portion refracted. The wave being thus sent back again produces a shock
in the opposite dir