he surface of these lavas is still very arid and bristling, and
is covered with black scoriae; so that it is not without great labor that
human industry has redeemed some small spots, and converted them into
vineyards. Upon the produce of these vineyards the population of the
island is almost entirely supported. It amounted when I was there, in
1828, to about twenty-five thousand, and was on the increase.

[Illustration: Fig 41.

Part of Ischia seen from the West.

_a._ Monte Epomeo or San Niccola.

_b._ Monte Vico.

_c._ Another of the minor cones with a crater.[492]]

From the date of the great eruption last alluded to, down to our own
time, Ischia has enjoyed tranquillity, with the exception of one
emission of lava hereafter to be described, which, although it
occasioned much local damage, does not appear to have devastated the
whole country, in the manner of more ancient explosions. There are, upon
the whole, on different parts of Epomeo, or scattered through the lower
tracts of Ischia, twelve considerable volcanic cones which have been
thrown up since the island was raised above the surface of the deep; and
many streams of lava may have flowed, like that of "Arso" in 1302,
without cones having been produced; so that this island may, for ages
before the period of the remotest traditions, have served as a
safety-valve to the whole Terra di Lavoro, while the fires of Vesuvius
were dormant.

_Lake Avernus._--It seems also clear that Avernus, a circular lake near
Puzzuoli, about half a mile in diameter, which is now a salubrious and
cheerful spot, once exhaled mephitic vapors, such as are often emitted
by craters after eruptions. There is no reason for discrediting the
account of Lucretius, that birds could not fly over it without being
stifled, although they may now frequent it uninjured.[493] There must
have been a time when this crater was in action; and for many centuries
afterwards it may have deserved the appellation of "atri jauna Ditis,"
emitting, perhaps, gases as destructive of animal life as those
suffocating vapors given out by Lake Quilotoa, in Quito, in 1797, by
which whole herds of cattle on its shores were killed,[494] or as those
deleterious emanations which annihilated all the cattle in the island of
Lancerote, one of the Canaries, in 1730.[495] Bory St. Vincent mentions,
that in the same isle birds fell lifeless to the ground; and Sir William
Hamilton informs us that he picked up dead birds on