e will come when it
will cease to burn; whether it be that some caverns become closed up by
the movements of the earth, or others opened, or whether the fuel is
finally exhausted.[3] Strabo may be regarded as having originated the
view, now generally held, that active volcanoes are safety-valves to the
regions in which they are situated. Referring to the tradition recorded
by Pliny, that Sicily was torn from Italy by an earthquake, he observes
that the land near the sea in those parts was rarely shaken by
earthquakes, since there are now orifices whereby fire and ignited
matters and waters escape; but formerly, when the volcanoes of Etna, the
Lipari Islands, Ischia, and others were closed up, the imprisoned fire
and wind might have produced far more violent movements.[4]

The account of the first recorded eruption of Vesuvius has been
graphically related by the younger Pliny in his two letters to Tacitus,
to which I shall have occasion to refer further on.[5] These bring down
the references to volcanic phenomena amongst ancient authors to the
commencement of the Christian era; from all of which we may infer that
the more enlightened philosophers of antiquity had a general idea that
eruptions had their origin in a central fire within the interior of the
earth, that volcanic mountains were liable to become dormant for long
periods, and afterwards to break out into renewed activity, that there
existed a connection between volcanic action and earthquakes, and that
volcanoes are safety-valves for the regions around.

It is unnecessary that I should pursue the historical sketch further.
Those who wish to know the views of writers of the Middle Ages will find
them recorded by Sir Charles Lyell.[6] The long controversy carried on
during the latter part of the eighteenth century between "Neptunists,"
led by Werner on the one side, and "Vulcanists," led by Hutton and
Playfair on the other, regarding the origin of such rocks as granite and
basalt, was finally brought to a close by the triumph of the
"Vulcanists," who demonstrated that such rocks are the result of igneous
fusion; and that in the cases of basalt and its congeners, they are
being extruded from volcanic vents at the present day. The general
principles for the classification of rocks as recognised in modern
science may be regarded as having been finally established by James
Hutton, of Edinburgh, in his _Theory of the Earth_,[7] while they were
illustrated and defended