ers and slaggy materials,
having a height above its floor of about 6600 feet, and a base the
diameter of which exceeds four miles.

The crater of Stromboli is situated, not at the apex of the cone, but at
a distance of 1000 feet below it. The explosions of steam, accompanied
by the roaring as of a smelting furnace, or of a railway engine when
blowing off its steam, are said by Judd to take place at very irregular
intervals of time, "varying from less than one minute to twenty minutes,
or even more." On the other hand, Hoffmann describes them as occurring
at "perfectly regular intervals," so that, perhaps, some variation has
taken place within the interval of about forty years between each
observation. Both observers agree in stating that lava is to be seen
welling up from some of the apertures within the crater, and pouring
down the slope towards the sea, which it seldom or never reaches.[5] The
intermittent character of these eruptions appears to be due, as Mr.
Scrope has suggested, to the exact proportion between the expansive and
repressive forces; the expansive force arising from the generation of a
certain amount of aqueous vapour and of elastic gas; the repressive,
from the pressure of the atmosphere and from the weight of the
superincumbent volcanic products. Steam is here, as in a steam-engine,
not the originating agent in the phenomena recorded; but the result of
water coming in contact with molten lava constantly welling up from the
interior, by which it is converted into steam, which from time to time
acquires sufficient elastic force to produce the eruptions; the water
being obviously derived from the surrounding sea, which finds its way by
filtration through fissures, or through the porous mass of which the
mountain is formed. Were it not for the access of water this volcano
would probably appear as a fissure-cone extruding a small and continuous
stream of molten lava. The adventitious access of the sea water gives
rise to the phenomena of intermittent explosions. The vitality of the
volcano is therefore due, not to the presence of water, but to the
welling up of matter from the internal reservoir through the throat of
the volcano.

_Pantelleria._--This island, lying between the coast of Sicily and Cape
Bon in Africa, is wholly volcanic. It has a circumference of thirty
miles, and from its centre rises an extinct crater-cone to a height of
about 3000 feet. The flanks of this volcano are diversified by seve