Extinct Volcanoes--Auvergne--Vienne--Agde--Eyfel--Italy--Lacus
Cimini--Grotto del Cane--Guevo Upas--Talaga Bodas--The Dead Sea.
There are two sorts of extinct volcanoes: _first_, those in
which all evidences of activity have entirely ceased; and,
_secondly_, those in which a subdued state of activity
lingers. The former are more widely distributed than the latter;
but sometimes both kinds occur in the same district of country.
Extinct volcanoes are found in the district of Auvergne in France.
Solidified streams of lava occur at Volvic near Riom; and the
crater whence they descended is still visible on the top of the Puy
de Nugere. It is an oblong basin, having its edge broken on the
side down which the lava flowed. In its descent the fiery stream
appears to have encountered a knoll of granite, by which it was
divided into two branches. These seem to have reunited lower down,
and thence to have overspread the valley beneath.
The Puy de Côme, a mountain near Clermont, appears to have sent
forth two streams of lava, which have effected considerable changes
in the surface of the country--blocking up the courses of rivers
diverting them into new channels, and forming swamps in the old. On
the top of Puy Pariou, to the north of Clermont, there exists a
perfect crater, quite round, and about two hundred and fifty feet
deep, whence there has flowed a stream of lava, whose course can be
distinctly traced. The summit of Puy Graveniere, a long round-backed
hill also near Clermont, consists almost entirely of a heap
of volcanic cinders, which have obliterated all traces of a crater;
but two streams of lava appear to have flowed from the sides of the
mountain. The Puy de Dôme, and the mountains in its neighbourhood,
likewise appear to be of volcanic origin, and to have been upheaved
somewhat in the same manner as Jorullo. Although the aspect of the
mountains of Auvergne indicates so clearly their having been active
since the surrounding country acquired its present general
conformation, neither history nor tradition has preserved any
record of their eruptions.
There is extant, however, a letter from Sidonius Apollinaris, a
cotemporary of Pliny, addressed to the Bishop of Vienne, in which
he refers to forms of prayer which had been appointed by the bishop
at the time when earthquakes demolished the walls of Vienne, and
the mountains, opening, vomited forth torrents of inflamed
materials. It hence appears that the extinct volcanoes in the
neighbourhood of Vienne, and perhaps those of Le Puy, had been in a
state of eruption not long after the beginning of the Christian
era. To the westward of the latter town, there is a number of small
volcanic craters, of which the two largest are the Lake de Bouchet
and the Crater of Bar, which also appears to have been at one time
a lake, but is now dry. The former has its greatest diameter about
2300 feet, with a depth of about 90 feet. The latter is on the top
of a mountain, which is composed entirely of such substances as are
ejected by volcanoes. Its diameter is about 1660, and its depth
about 130 feet; while it is almost perfect in its form. The
mountains near Vienne exhibit streams of lava, which accommodate
themselves to the existing valleys. Near Agde also, on the shores
of the Gulf of Lions, on the top of a hill named St. Loup, there is
an extinct crater, whence have descended two streams of lava
apparently of recent origin. On one of them the town of Agde has
been built; the other projects into the sea.
The district of Eyfel, on the borders of the Rhine, is another in
which extinct volcanoes abound. They occur mostly in the form of
circular craters, which are now filled with water, their borders
consisting of volcanic ejections. They also exhibit various
superficial streams of lava. One of the most remarkable of these
round craters lies near Andernuch, a little west of the Rhine. It
is named the Lake of Laach, and is nearly two miles in circumference.
On its margin are found numerous volcanic ejections, exactly
resembling those of Mount Vesuvius. Notwithstanding these
evidences that the extinct volcanoes of Eyfel have been in activity
since the country acquired its present conformation, there are no
historical records of their operations. There is, indeed, a passage
in Tacitus referring to fires that issued from the earth near
Cologne; but his description does not warrant the conclusion that
the event to which he alludes was of the nature of a volcanic
eruption. The Drachenfels on the eastern bank of the Rhine, and the
other mountains in its neighbourhood, belong to the more ancient
volcanic formations. The same may be affirmed of the other
mountains scattered throughout Germany and central Europe
generally, in which rocks of volcanic origin occur.
There are a good many traces of extinct volcanoes in Italy, besides
those of the Phlegræan fields already mentioned. In general
character they resemble those previously described. The chief
localities are certain lakes, near Volterra in Tuscany, which give
forth very hot sulphurous and boracic acid vapours; a small
sulphureous lake near Viterbo continually giving forth bubbles of
gas; the Lake of Vico between Viterbo and Rome; the mountain and
Lake of Albano near Rome; Mount Vultur in the Apennines, in the
province of the Basilicata; and Lake Agnano near Naples. Of these,
the Lakes of Vico and Agnano are the most interesting. The former
is the ancient Lacus Cimini, and old authors state that its site
was once occupied by a town, whose ruins used to be visible at the
bottom of the lake when the water was clear. The ground, with the
town upon it, is said to have been ingulfed during a volcanic
convulsion, when the lake was formed in its place.
The Lake Agnano is the site of an ancient volcanic crater, and on
its margin is situated the Grotto del Cane, so famous for the
deadly vapours it exhales. These consist of carbonic acid gas, in
combination with watery vapour. This celebrated Grotto is thus
described, in his work on volcanoes, by Dr. Daubeny, who visited
the spot:--
"The mouth of the cavern being somewhat more elevated than its
interior, a stratum of carbonic acid goes on constantly
accumulating at the bottom, but upon rising above the level of its
mouth, flows like so much water over the brim. Hence the upper part
of the cavern is free from any noxious vapour; but the air of that
below is so fully impregnated, that it proves speedily fatal to any
animal that is immersed in it, as is shown to all strangers by the
experiment with the dog.
"The sensation I experienced, on stooping my head for a moment to
the bottom, resembled that of which we are sometimes sensible on
drinking a large glass of soda water in a state of brisk
effervescence. The cause in both instances is plainly the same.
"The quantity of carbonic acid present in the cavern at various
heights, was shown by immersing in it various combustibles in a
state of inflammation. I found that phosphorus would continue
lighted at about two feet from the bottom, whilst a sulphur match
went out a few inches above, and a wax taper at a still higher
level.
"It was impossible to fire a pistol at the bottom of the cavern,
for although gunpowder may be exploded even in carbonic acid by the
application of a heat sufficient to decompose the nitre, and
consequently to envelop the mass in an atmosphere of oxygen gas,
yet the mere influence of a spark from steel produces too slight an
augmentation of temperature for this purpose."
Similar phenomena, but on a grander scale, are presented by the
extinct crater in the Island of Java called "Guevo Upas," the
Poison-Valley. It is a level about half a mile in circumference,
surrounded by precipitous rocks. From various parts of its soil
carbonic acid gas is discharged in such quantities as to prove
fatal to any animal venturing nigh. The ground is consequently
strown with numerous skeletons. This valley gave rise to the famous
figment about the upas-tree, which once obtained such general
belief in Europe.
There is another extinct crater in Java, whence are exhaled vapours
equally deadly, but which exert a most peculiar effect on the dead
carcasses subjected to their influence. Instead of their being, as
in the Gruevo Upas, reduced to skeletons, the carcasses have all
their bones dissolved by the vapours; while the flesh, skin, hair,
and nails are by their action preserved from decay. This remarkable
crater is situated near the volcano of Talaga Bodas.
Of all the extinct volcanoes in the world, however, none is so
remarkable as the Dead Sea. That singular collection of salt and
bitter water has the level of its surface depressed 1312 feet below
that of the Mediterranean--thus indicating an enormous subsidence.
The Dead Sea occupies the site of what was formerly the plain of
Jordan, described as having been "well-watered everywhere, as the
garden of the Lord, like the land of Egypt." One part of it, called
the Vale of Siddim, was full of slime-pits--the only indications of
volcanic action. When the cities of Sodom and Gomorrah, which stood
in the plain, were destroyed, the Lord, it is said, rained upon
them fire and brimstone from heaven; but while these fell upon the
cities from the atmosphere, it appears that they must have
primarily been discharged from the earth; for "the smoke of the
country went up as the smoke of a furnace." The phenomena,
therefore, most likely resembled, in the first instance, those of
Jorullo; but the catastrophe seems to have ended like the last
great eruption of the volcano in Timor--the whole of the plain
having been ingulfed and replaced by the salt lake, whose depressed
level so clearly indicates the nature of its origin.