formed a part of such a
marine accumulation. On the contrary, all the usual signs of subaqueous
origin are wanting; and even if we believe the foundations of the
mountain to have been laid in the sea, we could not expect this portion
to be made visible in sections which only proceed downwards from the
summit through one-half the thickness of the mountain, especially as the
highest points attained by the tertiary strata in other parts of Sicily
very rarely exceed 3000 feet above the sea.

On the eastern and southern base of Etna, a marine deposit, already
alluded to, is traced up to the height of 800 or 1000 feet, before it
becomes concealed beneath that covering of modern lavas which is
continually extending its limits during successive eruptions, and
prevents us from ascertaining how much higher the marine strata may
ascend. As the imbedded shells belong almost entirely to species now
inhabiting the Mediterranean, it is evident that there has been here an
upheaval of the region at the base of Etna at a very modern period. It
is fair, therefore, to infer that the volcanic nucleus of the mountain,
partly perhaps of submarine, and partly of subaerial origin,
participated in this movement, and was carried up bodily. Now, in
proportion as a cone gains height by such a movement, combined with the
cumulative effects of eruptions, throwing out matter successively from
one or more central vents, the hydrostatic pressure of the columns of
lava augments with their increasing height, until the time arrives when
the flanks of the cone can no longer resist the increased pressure; and
from that period they give way more readily, lateral outbursts becoming
more frequent. Hence, independently of any local expansion of the
fractured volcanic mass, those general causes by which the modern
tertiary strata of a great part of Sicily have been raised to the height
of several thousand feet above their original level, would tend
naturally to render the discharge of lava and scoriae from the summit of
Etna less copious, and the lateral discharge greater.

If, then, a conical or dome-shaped mass of volcanic materials was
accumulated to the height of 4000, or perhaps 7000 feet, before the
upward movement began, or, what is much more probable, during the
continuance of the upward movement, that ancient mass would not be
buried under the products of newer eruptions, because these last would
then be poured out chiefly at a lower level.

Since I