be seen relieved by clouds of fleecy vapor which settle behind
them, and do not disperse until mid-day, continuing to fill the valley
while the sun is shining on every other part of Sicily, and on the
higher regions of Etna.

As soon as the vapors begin to rise, the changes of scene are varied in
the highest degree, different rocks being unveiled and hidden by turns,
and the summit of Etna often breaking through the clouds for a moment
with its dazzling snows, and being then as suddenly withdrawn from the
view.

An unusual silence prevails; for there are no torrents dashing from the
rocks, nor any movement of running water in this valley such as may
almost invariably be heard in mountainous regions. Every drop of water
that falls from the heavens, or flows from the melting ice and snow, is
instantly absorbed by the porous lava; and such is the dearth of
springs, that the herdsman is compelled to supply his flocks, during
the hot season, from stores of snow laid up in hollows of the mountain
during winter.

The strips of green herbage and forest land, which have here and there
escaped the burning lavas, serve, by contrast, to heighten the
desolation of the scene. When I visited the valley, nine years after the
eruption of 1819, I saw hundreds of trees, or rather the white skeletons
of trees, on the borders of the black lava, the trunks and branches
being all leafless, and deprived of their bark by the scorching heat
emitted from the melted rock; an image recalling those beautiful
lines:--

----"As when heaven's fire
Hath scath'd the forest oaks, or mountain pines,
With singed top their stately growth, though bare,
Stands on the blasted heath."

[Illustration: Fig. 49.

Dikes at the base of the Serre del Solfizio, Etna.]

_Form, composition, and origin of the dikes._--But without indulging the
imagination any longer in descriptions of scenery, I may observe that
the dikes before mentioned form unquestionably the most interesting
geological phenomenon in the Val del Bove. Some of these are composed of
trachyte, others of compact blue basalt with olivine. They vary in
breadth from two to twenty feet and upwards, and usually project from
the face of the cliffs, as represented in the annexed drawing (fig. 49).
They consist of harder materials than the strata which they traverse,
and therefore waste away less rapidly under the influence of that
repeated congelation and thawing to which the rocks in this z