is said, acquires confirmation from the fact, that the
sheets of lava near the summit of Somma are so compact and crystalline,
and of such breadth individually, as would not have been the case had
they run down a steep slope. They must, therefore, have consolidated on
a nearly level surface, and have been subsequently uplifted into their
present inclined position.

Unfortunately there are no sections of sufficient depth and continuity
on the flanks of Somma, to reveal to us clearly the relations of the
lava, scoriae, and associated dikes, forming the highest part of the
mountain, with the marine tuffs observed on its declivity. Both may,
perhaps, have been produced contemporaneously when Somma raised its
head, like Stromboli, above the sea, its sides and base being then
submerged. Such a state of things may be indicated by a fact noticed by
Von Buch, namely, that the pumiceous beds of Naples, when they approach
Somma, contain fragments of the peculiar leucitic lava proper to that
mountain, which are not found in the same tuff at a greater
distance.[535] Portions, therefore, of this lava were either thrown out
by explosions, or torn off by the waves, during the deposition of the
pumiceous strata beneath the sea.

We have as yet but a scanty acquaintance with the laws which regulate
the flow of lava beneath water, or the arrangement of scoriae and
volcanic dust on the sides of a submarine cone. There can, however, be
little doubt that showers of ejected matter may settle on a steep slope,
and may include shells and the remains of aquatic animals, which
flourish in the intervals between eruptions. Lava under the pressure of
water would be less porous; but, as Dr. Daubeny suggests, it may retain
its fluidity longer than in the open air; for the rapidity with which
heated bodies are cooled by being plunged into water arises chiefly from
the conversion of the lower portions of water into steam, which steam
absorbing much heat, immediately ascends, and is reconverted into water.
But under the pressure of a deep ocean, the heat of the lava would be
carried off more slowly, and only by the circulation of ascending and
descending currents of water, those portions nearest the source of heat
becoming specifically light, and consequently displacing the water
above. This kind of circulation would take place with much less rapidity
than in the atmosphere, inasmuch as the expansion of water by equal
increments of heat is less conside