disappeared. So, too, a large part of the ash and much of the lava has
been swept away by the streams which drain the region, and which in
times of eruption are greatly swollen by the accompanying torrential
rains. The writer has estimated that if all the emanations from the
volcano--solid, fluid, and gaseous--could be heaped on the cone, they
would form a mass of between two and three thousand cubic miles in
contents. Yet notwithstanding this enormous outputting of earthy
matter, the earth on which the Ætnean cone has been constructed has
not only failed to sink down, but has been in process of continuous,
slow uprising, which has lifted the surface more than a thousand feet
above the level which it had at the time when volcanic action began in
this field. Here, even more clearly than in the case of Vesuvius, we
see that the materials driven forth from the crater are derived not
from just beneath its foundation, but from a distance, from realms
which in the case of this insular volcano are beneath the sea floors.
It is certain that here the migration of rock matter, impelled by the
expansion of its contained water toward the vent, has so far exceeded
that which has been discharged through the crater that an uprising of
the surface such as we have observed has been brought about.

[Illustration: _Mount Ætna, seen from near Catania. The imperfect
cones on the sky line to the left are those of small secondary
eruptions._]

There are certain peculiarities of Mount Ætna which are due in part to
its great size and in part to the climatal conditions of the region in
which it lies. The upper part of the mountain in winter is deeply
snow-clad; the frozen water often, indeed, forms great drifts in the
gorges near the summit. Here it has occasionally happened that a layer
of ashes has deeply buried the mass, so that it has been preserved for