ht of twenty or thirty feet in
a perfectly regular manner, and as if it were pushed up by a force
beneath, which suddenly exploded with a loud noise, and scattered about
a volume of black mud in every direction. After an interval of two or
three, or sometimes four or five seconds, the hemispherical body of mud
rose and exploded again. In the manner stated this volcanic ebullition
goes on without interruption, throwing up a globular body of mud, and
dispersing it with violence through the neighboring plain. The spot
where the ebullition occurs is nearly circular, and perfectly level. It
is covered only with the earthy particles, impregnated with salt water,
which are thrown up from below. The circumference may be estimated at
about half an English mile. In order to conduct the salt water to the
circumference, small passages or gutters are made in the loose muddy
earth, which lead to the borders, where it is collected in holes dug in
the ground for the purpose of evaporation."

The mud has a strong, pungent, sulphurous smell, resembling that of
mineral oil, and is hotter than the surrounding atmosphere. During the
rainy season the explosions increase in violence.

There are submarine mud volcanoes as well as those of igneous kind. In
1814 one of this character broke out in the Sea of Azof, beginning with
flame and black smoke, accompanied by earth and stones, which were flung
to a great height. Ten of these explosions occurred, and, after a period
of rest, others were heard during the night. The next morning there
was visible above the water an island of mud some ten feet high. A very
similar occurrence took place in 1827, near Baku, in the Caspian sea.
This began with a flaming display and the ejection of great fragments of
rock. An eruption of mud succeeded. A set of small volcanoes discovered
by Humboldt in Turbaco, in South America, confined their emissions
almost wholly to gases, chiefly nitrogen.

There is a close connection in character between mud volcanoes and
those intermittent boiling springs named geysers. A good many of the mud
volcanoes throw out jets of boiling water along with the mud; but in
the case of the geysers, the boiling water is ejected alone, without
any visible impregnation, though some mineral in solution, as silica,
carbonate of lime, or sulphur, is usually present.

THE GEYSER IS A WATER VOLCANO

The phenomenon of the geyser serves in a measure to support the theory
that steam is an