ession of a volcano is indicated in the title of "burning
mountain," so often employed, a great fire-spouting cone of volcanic
debris, from which steam, lava, rock-masses, cinder-like fragments, and
dust, often of extreme fineness, are flung high into the air or flow
in river-like torrents of molten rock. This, no doubt, applies in the
majority of cases, but the volcanic forces do not confine themselves to
these magnificent displays of energy, nor are their products limited to
those above specified. We have seen that mud is a not uncommon product,
due to the mingling of water with volcanic dust, while water alone is
occasionally emitted, of which we have a marked instance in the Volcan
de Agua, of Guatemala, already mentioned. As regards mud flows, we may
specially instance the first outflow from Mont Pelee, that by which the
Guerin sugar works were overwhelmed.

The imprisoned forces of the earth have still other modes of
manifestation. A very frequent one of these, and the most destructive to
human life of them all, is the earthquake.

Minor manifestations of volcanic action may be seen in the geyser and
the hot spring, the latter the most widely disseminated of all the
resultant effects of the heated condition of the earth's interior. It
is these displays of subterranean energy, differing from those usually
termed volcanic, yet due to the same general causes, that we have next
to consider. And it may be premised that their manifestations, while,
except in the case of the earthquake, less violent, are no less
interesting, especially as the minor displays are free from that peril
to human life which renders the major ones so terrible.

While the largest volcanoes at times pour out rivers of liquid mud,
there are volcanoes from which nothing is ever ejected but mud and
water, the latter being generally salt. From this circumstance they
are sometimes called salses, but they are more generally termed
mud-volcanoes. Some varieties of them throw out little else than gases
of different sorts, and these are called air-volcanoes.

THE GREAT MUD VOLCANO OF SICILY

One of the best known mud-volcanoes is at Macaluba, near Girgenti, in
Sicily. It consists of several conical mounds, varying from time to time
in their form and height, which ranges from eight to thirty feet. From
orifices on the tops of these mounds there are thrown out sometimes jets
of warmish water and mud mixed with bitumen, sometimes bubbles of
gas, chi