Physical geography. By Mary Somerville ...

CHAP. XIII. ACTIVE VOLCANOES. 155
hot springs, and vapours. In the range of Targatabai, in the country of the Kirghiz, there is a mount said to emit smoke and even
flame, which produces sulphur and sal-ammoniac in abundance. It
is not ascertained that there are many mountains in China that eject
lava, but there are many fire-hills and fire-springs; the latter are
real Artesian wells, five or six inches wide, and from 1500 to 3000
feet deep: from some of these water rises containing a great quantity of common salt; from others gases issue: and when a flame is
applied, fire rushes out with great violence, rising 20 or 30 feet high,
with a noise like thunder. The gas, conducted in tubes of bamboo
cane, is used in the evaporation of salt water from the neighbouring
springs.
There are altogether about 270 active volcanoes, of which 190
are on the shores and islands of the Pacific. They are generally
disposed in lines or groups. The chain of the Andes furnishes a
magnificent example of linear volcanoes. The peak of Teneriffe,
encompassed by the volcanic islands of Palma and Lancerote, is an
equally good specimen of a central group. Eruptions are much
more frequent in low than in high volcanoes; that in the island of
Stromboli is in constant activity; whereas Cotopaxi, 18,875 feet
high, and Tungaragua, 16,424, in the Andes, have only been active
once in a hundred years. On account of the force requisite to raise
lava to such great elevations, it rarely flows from very elevated cones.
Antisana is the only instance to the contrary among all the lofty
volcanoes of Equatorial America. In Etna also the pressure is so
great that the lava forces its way through the sides of the mountain,
or at the base of the cone.
An explosion begins by a dense volume of smoke issuing from
the crater, mixed with aqueous vapour and gases, then masses of
rock and molten matter in a half-fluid state are ejected with tremendous explosion and violence; after which lava begins to flow,
and the whole terminates by a shower of ashes from the crateroften the most formidable part of the phenomenon, as was experienced at the destruction of Pompeii. There are several volcanoes
which eject only streams of boiling water, as the Volcano de Agua
in Guatemala; others pour forth boiling mud, as in the islands of
Trinidad, Java, and Cheduba in the Bay of Bengal. A more feeble
effort of the volcanic force appears in the numerous solfataras. Hot
springs show that the volcanic fire is not extinguished, though not
otherwise apparent. To these may be added acidulous springs, those
of naphtha, petroleum, and various kinds of gas, as carbonic acid
gas, the food of plants-and, when breathed, the destruction of animals, as is fearfully seen in the Guero Upas, or Valley of Death,"
in Java: it is half a mile in circumference and about 35 feet deep,
with a few large stones, and not a vestige of vegetation on the bottom,
which is covered with the skeletons of human beings and the bones