f
Biscari; so that the traveller may now see the solid lava curling over
the top of the rampart as if still in the very act of falling.

This great current performed the first thirteen miles of its course in
twenty days, or at the rate of 162 feet per hour, but required
twenty-three days for the last two miles, giving a velocity of only
twenty-two feet per hour; and we learn from Dolomieu that the stream
moved during part of its course at the rate of 1500 feet an hour, and in
others it took several days to cover a few yards.[564] When it entered
the sea it was still six hundred yards broad, and forty feet deep. It
covered some territories in the environs of Catania which had never
before been visited by the lavas of Etna. While moving on, its surface
was in general a mass of solid rock; and its mode of advancing, as is
usual with lava streams, was by the occasional fissuring of the solid
walls. A gentleman of Catania, named Pappalardo, desiring to secure the
city from the approach of the threatening torrent, went out with a party
of fifty men whom he had dressed in skins to protect them from the heat,
and armed with iron crows and hooks. They broke open one of the solid
walls which flanked the current near Belpasso, and immediately forth
issued a rivulet of melted matter which took the direction of Paterno;
but the inhabitants of that town, being alarmed for their safety, took
up arms and put a stop to farther operations.[565]

As another illustration of the solidity of the walls of an advancing
lava stream, I may mention an adventure related by Recupero, who, in
1766, had ascended a small hill formed of ancient volcanic matter, to
behold the slow and gradual approach of a fiery current, two miles and a
half broad; when suddenly two small threads of liquid matter issuing
from a crevice detached themselves from the main stream, and ran rapidly
towards the hill. He and his guide had just time to escape, when they
saw the hill, which was fifty feet in height, surrounded, and in a
quarter of an hour melted down into the burning mass, so as to flow on
with it.

But it must not be supposed that this complete fusion of rocky matter
coming in contact with lava is of universal, or even common, occurrence.
It probably happens when fresh portions of incandescent matter come
successively in contact with fusible materials. In many of the dikes
which intersect the tuffs and lavas of Etna, there is scarcely any
perceptible alterati