scent, made an
inconceivable crash as it was dashed against the bottom. So immense was
the column of dust raised by the abrasion of the tufaceous hill over
which the hardened mass descended, that the Catanians were in great
alarm, supposing a new eruption to have burst out in the woody region,
exceeding in violence that near the summit of Etna.

[Illustration: Fig. 52.

View from the summit of Etna into the Val del Bove.[569]]

_Mode of advance of the lava._--Of the cones thrown up during this
eruption, not more than two are of sufficient magnitude to be numbered
among those eighty which were before described as adorning the flanks of
Etna. The surface of the lava which deluged the "Val del Bove," consists
of rocky and _angular blocks_, tossed together in the utmost disorder.
Nothing can be more rugged, or more unlike the smooth and even
superficies, which those who are unacquainted with volcanic countries
may have pictured to themselves, in a mass of matter which had
consolidated from a liquid state. Mr. Scrope observed this current in
the year 1819, slowly advancing down a considerable slope, at the rate
of about a yard an hour, nine months after its emission. The lower
stratum being arrested by the resistance of the ground, the upper or
central part gradually protruded itself, and, being unsupported, fell
down. This in its turn was covered by a mass of more liquid lava, which
swelled over it from above. The current had all the appearance of a huge
heap of rough and large cinders rolling over and over upon itself by the
effect of an extremely slow propulsion from behind. The contraction of
the crust as it solidified, and the friction of the scoriform cakes
against one another, produced a crackling sound. Within the crevices a
dull red heat might be seen by night, and vapor issuing in considerable
quantity was visible by day.[570]

It was stated that when the lava of 1819 arrived at the head of the
Valley of Calanna, after flowing down the Val del Bove, it descended in
a cascade. This stream, in fact, like many previous currents of lava
which have flowed down successively from the higher regions of Etna, was
turned by a great promontory projecting from the southern side of the
Val del Bove. This promontory consists of the hills called Zocolaro and
Calanna, and of a ridge of inferior height which connects them. (See
fig. 53.)

[Illustration: Fig. 53.

A, Zocolaro.
B, Monte di Calanna.
C, Plain at the he