between the particles of the material.

If we consider the Italian volcanoes as a whole, we find that they lie
in a long, discontinuous line extending from the northern part of the
valley of the Po, within sight of the Alps, to Ætna, and in
subterranean cones perhaps to the northern coast of Africa. At the
northern end of the line we have a beautiful group of extinct
volcanoes, known as the Eugean Mountains. Thence southward to southern
Tuscany craters are wanting, but there is evidence of fissures in the
earth which give forth thermal waters. From southern Tuscany southward
through Rome to Naples there are many extinct craters, none of which
have been active in the historic period. From Naples southward the
cones of this system, about a dozen in number, are on islands or close
to the margin of the sea. It is a noteworthy fact that the greater
part of these shore or insular vents have been active since the dawn
of history; several of them frequently and furiously so, while none of
those occupying an inland position have been the seat of explosions.
This is a striking instance going to show the relation of these
processes to conditions which are brought about on the sea bottom.

Ætna is, as we have noticed, a much more powerful volcano than
Vesuvius. Its outbreaks are more vigorous, its emanations vastly
greater in volume, and the mass of its constructions many times as
great as those accumulated in any other European cone. There are,
however, a number of volcanoes in the world which in certain features
surpass Ætna as much as that crater does Vesuvius. Of these we shall
consider but two--Skaptar Jokul, of Iceland, remarkable for the volume
of its lava flow, and Krakatoa, an island volcano between Java and
Sumatra, which was the seat of the greatest explosion of which we have
any record.