t highest cone, which has been
several times destroyed and renewed. The precipices seen at the head of
the Val del Bove, in the escarpment called the Serre del Solfizio,
exhibit merely the same series of alternating lavas and breccias, which,
descending with a general dip towards the sea, form the boundary cliffs
of all other parts of the Val del Bove. If then we estimate the height
of Etna at about 11,000 feet, we may say that we know from actual
observation less than one-half of its component materials, assuming it
to extend downwards to the level of the sea; namely, first, the highest
cone, which is about 1000 feet above its base; and, secondly, the
alternations of lava, tuff, and volcanic breccia, which constitute the
rocks between the Cisterna, near the base of the upper cone, and the
foot of the precipices at the head of the Val del Bove. At the lowest
point to which the vertical section extends, there are no signs of any
approach to a termination of the purely volcanic mass, which may perhaps
penetrate many thousand feet farther downwards. There is, indeed, a rock
called Rocca Gianicola, near the foot of the great escarpment, which
consists of a large mass between 150 and 200 feet wide, not divided into
beds, and almost resembling granite in its structure, although agreeing
very closely in mineral composition with the lavas of Etna in
general.[574] This mass may doubtless be taken as a representative of
those crystalline or plutonic formations which would be met with in
abundance if we could descend to greater depths in the direction of the
central axis of the mountain. For a great body of geological evidence
leads us to conclude, that rocks of this class result from the
consolidation, under great pressure, of melted matter, which has risen
up and filled rents and chasms, such, for example, as may communicate
with the principal and minor vents of eruption in a volcano like Etna.

But, if we speculate on the nature of the formation which the lava may
have pierced in its way upwards, we may fairly presume that a portion of
these consist of marine tertiary rocks, like those of the neighboring
Val di Noto, or those which skirt the borders of the Etnean cone, on its
southern and eastern sides. Etna may, in fact, have been at first an
insular volcano, raising its summit but slightly above the level of the
sea; but we have no grounds for concluding that any of the beds exposed
in the deep section of the Val del Bove have