Volcanic
region extending from Central Asia to the Azores--Tradition of
deluges on the shores of the Bosphorus, Hellespont, and Grecian
isles--Periodical alternation of earthquakes in Syria and Southern
Italy--Western limits of the European region--Earthquakes rarer and
more feeble as we recede from the centres of volcanic action.
Extinct volcanoes not to be included in lines of active vents.

We have hitherto considered the changes wrought, since the times of
history and tradition, by the continued action of aqueous causes on the
earth's surface; and we have next to examine those resulting from
igneous agency. As the rivers and springs on the land, and the tides and
currents in the sea, have, with some slight modifications, been fixed
and constant to certain localities from the earliest periods of which we
have any records, so the volcano and the earthquake have, with few
exceptions, continued, during the same lapse of time, to disturb the
same regions. But as there are signs, on almost every part of our
continent, of great power having been exerted by running water on the
surface of the land, and by waves, tides, and currents on cliffs
bordering the sea, where, in modern times, no rivers have excavated, and
no waves or tidal currents undermined--so we find signs of volcanic
vents and violent subterranean movements in places where the action of
fire or internal heat has long been dormant. We can explain why the
intensity of the force of aqueous causes should be developed in
succession in different districts. Currents, for example, tides, and the
waves of the sea, cannot destroy coasts, shape out or silt up estuaries,
break through isthmuses, and annihilate islands, form shoals in one
place, and remove them from another, without the direction and position
of their destroying and transporting power becoming transferred to new
localities. Neither can the relative levels of the earth's crust, above
and beneath the waters, vary from time to time, as they are admitted to
have varied at former periods, and as it will be demonstrated that they
still do, without the continents being, in the course of ages, modified,
and even entirely altered, in their external configuration. Such events
must clearly be accompanied by a complete change in the volume,
velocity, and direction of the streams and land floods to which certain
regions give passage. That we should find, therefore, cliffs where the
sea once com