ficiency of our records during that brief period, how important must
we presume the physical revolutions to have been in the course of thirty
or forty centuries, during which some countries habitually convulsed by
earthquakes have been peopled by civilized nations! Towns engulfed
during one earthquake may, by repeated shocks, have sunk to great depths
beneath the surface, while the ruins remain as imperishable as the
hardest rocks in which they are inclosed. Buildings and cities,
submerged, for a time, beneath seas or lakes, and covered with
sedimentary deposits, must, in some places, have been re-elevated to
considerable heights above the level of the ocean. The signs of these
events have, probably, been rendered visible by subsequent mutations, as
by the encroachments of the sea upon the coast, by deep excavations made
by torrents and rivers, by the opening of new ravines, and chasms, and
other effects of natural agents, so active in districts agitated by
subterranean movements.

If it be asked why, if such wonderful monuments exist, so few have
hitherto been brought to light, we reply--because they have not been
searched for. In order to rescue from oblivion the memorials of former
occurrences, the inquirer must know what he may reasonably expect to
discover, and under what peculiar local circumstances. He must be
acquainted with the action and effect of physical causes, in order to
recognize, explain, and describe correctly the phenomena when they
present themselves.

The best known of the great volcanic regions, of which the boundaries
were sketched in the twenty-second chapter, is that which includes
Southern Europe, Northern Africa, and Central Asia; yet nearly the
whole, even of this region, must be laid down, in a geological map, as
"Terra Incognita." Even Calabria may be regarded as unexplored, as also
Spain, Portugal, the Barbary States, the Ionian Isles, Asia Minor,
Cyprus, Syria, and the countries between the Caspian and Black seas. We
are, in truth, beginning to obtain some insight into one small spot of
that great zone of volcanic disturbance, the district around Naples; a
tract by no means remarkable for the violence of the earthquakes which
have convulsed it.

If, in this part of Campania, we are enabled to establish that
considerable changes in the relative level of land and sea have taken
place since the Christian era, it is all that we could have expected;
and it is to recent antiquarian and geolo