nd 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.

AEtna 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 AEtna 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.

The whole of Iceland may be regarded as a volcanic mass composed
mainly of lavas and ashes which have been thrown up by a group of
volcanoes lying near the northern end of the long igneous axis which
extends through the centre of the Atlantic. The island has been the
seat of numerous eruptions; in fact, since its settlement by the
Northmen in 1070 its sturdy inhabitants have been almost as much
distressed by the calamities which have come from the internal heat as
they have been by the enduring external cold. They have, indeed, been
between frost and fire. The greatest recorded eruption of Iceland
occurred in 1783, when the volcano of Skaptar, near the southern
border of the island, poured forth, first, a vast discharge of dust
and ashes, and afterward in the languid state of eruption inundated a
series of valleys with the greatest lava flow of which we have any
written record. The dust poured forth into the upper air, being finely
divided and