ection, doing great damage to buildings on the
surface by thus returning upon itself. At the same time, the shocks are
at once eased when they get into the more elastic materials of the
granitic mountains.

The surface of the country during the Calabrian earthquakes often heaved
like the billows of a swelling sea, which produced a swimming in the
head, like sea-sickness. It is particularly stated, in almost all the
accounts, that just before each shock the clouds appeared motionless;
and, although no explanation is offered of this phenomenon, it is
obviously the same as that observed in a ship at sea when it pitches
violently. The clouds seem arrested in their career as often as the
vessel rises in a direction contrary to their course; so that the
Calabrians must have experienced precisely the same motion on the land.

Trees, supported by their trunks, sometimes bent during the shocks to
the earth, and touched it with their tops. This is mentioned as a
well-known fact by Dolomieu; and he assures us that he was always on his
guard against the spirit of exaggeration in which the vulgar are ever
ready to indulge when relating these wonderful occurrences.

It is impossible to suppose that these waves, which are described in
Italy and other regions of earthquakes as passing along the solid
surface of the earth in a given direction like a billow on the sea, have
any strict analogy with the undulations of a fluid. They are doubtless
the effects of vibrations, radiating from some deep-seated point, each
of which on reaching the surface lifts up the ground, and then allows it
again to subside. As the distance between the source of the subterranean
movement and the surface must vary according to the outline of the
country, so the vibratory jar will reach different points in succession.

[Illustration: Fig. 75.

Shifts in the stones of two obelisks in the Convent of St Bruno.]

The Academicians relate that in some of the cities of Calabria effects
were produced seeming to indicate a whirling or vorticose movement.
Thus, for example, two obelisks (fig. 75) placed at the extremities of a
magnificent facade in the convent of S. Bruno, in a small town called
Stefano del Bosco, were observed to have undergone a movement of a
singular kind. The shock which agitated the building is described as
having been horizontal and vorticose. The pedestal of each obelisk
remained in its original place; but the separate stones above were
turne