onte Nuovo thrown
up--Uniformity of the volcanic operations of Vesuvius and Phlegraean
Fields in ancient and modern times.

I shall next give a sketch of the history of some of the volcanic vents
dispersed throughout the great regions before described, and consider
the composition and arrangement of their lavas and ejected matter. The
only volcanic region known to the ancients was that of the
Mediterranean; and even of this they have transmitted to us very
imperfect records relating to the eruptions of the three principal
districts, namely, that round Naples, that of Sicily and its isles, and
that of the Grecian Archipelago. By far the most connected series of
records throughout a long period relates to the first of these
provinces; and these cannot be too attentively considered, as much
historical information is indispensable in order to enable us to obtain
a clear view of the connection and alternate mode of action of the
different vents in a single volcanic group.

_Early convulsions in the Island of Ischia._---The Neapolitan volcanoes
extend from Vesuvius, through the Phlegraean Fields, to Procida and
Ischia, in a somewhat linear arrangement, ranging from the northeast to
the southwest, as will be seen in the annexed map of the volcanic
district of Naples (fig. 40). Within the space above limited, the
volcanic force is sometimes developed in single eruptions from a
considerable number of irregularly scattered points; but a great part of
its action has been confined to one principal and habitual vent,
Vesuvius or Somma. Before the Christian era, from the remotest periods
of which we have any tradition, this principal vent was in a state of
inactivity. But terrific convulsions then took place from time to time
in Ischia (Pithecusa), and seem to have extended to the neighboring isle
of Procida (Prochyta); for Strabo[490] mentions a story of Procida
having been torn asunder from Ischia; and Pliny[491] derives its name
from its having been poured forth by an eruption from Ischia.

The present circumference of Ischia along the water's edge is eighteen
miles, its length from west to east about five, and its breadth from
north to south three miles. Several Greek colonies which settled there
before the Christian era were compelled to abandon it in consequence of
the violence of the eruptions. First the Erythraeans, and afterwards the
Chalcidians, are mentioned as having been driven out by earthquakes and
igneous