n in the plain of S. Lio. A fissure six feet broad, and
of unknown depth, opened with a loud crash, and ran in a somewhat
tortuous course to within a mile of the summit of Etna. Its direction
was from north to south, and its length twelve miles. It emitted a most
vivid light. Five other parallel fissures of considerable length
afterwards opened, one after the other, and emitted smoke, and gave out
bellowing sounds which were heard at the distance of forty miles. This
case seems to present the geologist with an illustration of the manner
in which those continuous dikes of vertical porphyry were formed, which
are seen to traverse some of the older lavas of Etna; for the light
emitted from the great rent of S. Lio appears to indicate that the
fissure was filled to a certain height with incandescent lava, probably
to the height of an orifice not far distant from Monti Rossi, which at
that time opened and poured out a lava current. When the melted matter
in such a rent has cooled, it must become a solid wall or dike,
intersecting the older rocks of which the mountain is composed; similar
rents have been observed during subsequent eruptions, as in 1832, when
they ran in all directions from the centre of the volcano. It has been
justly remarked by M. Elie de Beaumont, that such star-shaped fractures
may indicate a slight upheaval of the whole of Etna. They may be the
signs of the stretching of the mass, which may thus be raised gradually
by a force from below.[563]

The lava current of 1669, before alluded to, soon reached in its course
a minor cone called Mompiliere, at the base of which it entered a
subterranean grotto, communicating with a suite of those caverns which
are so common in the lavas of Etna. Here it appears to have melted down
some of the vaulted foundations of the hill, so that the whole of that
cone became slightly depressed and traversed by numerous open fissures.

_Part of Catania destroyed._--The lava, after overflowing fourteen towns
and villages, some having a population of between three and four
thousand inhabitants, arrived at length at the walls of Catania. These
had been purposely raised to protect the city; but the burning flood
accumulated till it rose to the top of the rampart, which was sixty feet
in height, and then it fell in a fiery cascade and overwhelmed part of
the city. The wall, however, was not thrown down, but was discovered
long afterwards by excavations made in the rock by the Prince o