fourteenth; and of Monte Nuovo in the
sixteenth; but the eighteenth has formed an exception to this rule, and
this seems accounted for by the unprecedented number of eruptions of
Vesuvius during that period; whereas, when the new vents opened, there
had always been, as we have seen, a long intermittence of activity in
the principal volcano.

CHAPTER XXIV.

VOLCANIC DISTRICT OF NAPLES--_continued_.

Dimensions and structure of the cone of Vesuvius--Fluidity and
motion of lava--Dikes--Alluviums called "aqueous lavas"--Origin and
composition of the matter enveloping Herculaneum and
Pompeii--Condition and contents of the buried cities--Small number
of skeletons--State of preservation of animal and vegetable
substances--Rolls of papyrus--Stabiae--Torre del Greco--Concluding
remarks on the Campanian volcanoes.

_Structure of the cone of Vesuvius._--Between the end of the eighteenth
century and the year 1822, the great crater of Vesuvius had been
gradually filled by lava boiling up from below, and by scoriae falling
from the explosions of minor mouths which were formed at intervals on
its bottom and sides. In place of a regular cavity, therefore, there was
a rough and rocky plain, covered with blocks of lava and scoriae, and cut
by numerous fissures, from which clouds of vapor were evolved. But this
state of things was totally changed by the eruption of October, 1822,
when violent explosions, during the space of more than twenty days,
broke up and threw out all this accumulated mass, so as to leave an
immense gulf or chasm, of an irregular, but somewhat elliptical shape,
about three miles in circumference when measured along the very sinuous
and irregular line of its extreme margin, but somewhat less than three
quarters of a mile in its longest diameter, which was directed from N.
E. to S. W.[518] The depth of this tremendous abyss has been variously
estimated; for from the hour of its formation it increased daily by the
dilapidation of its sides. It measured, at first, according to the
account of some authors, two thousand feet in depth from the extreme
part of the existing summit;[519] but Mr. Scrope, when he saw it, soon
after the eruption, estimated its depth at less than half that amount.
More than eight hundred feet of the cone was carried away by the
explosions, so that the mountain was reduced in height from about 4200
to 3400 feet.[520]

As we ascend the sloping sides, the v