The reaction of the interior of
the earth on its external surface is exhibited with totally different force
in true volcanoes or igneous mountains, at points of the earth in which a
permanent, or, at least, continually-renewed connection with the volcanic
force is manifested. We must here carefully distinguish between the more or
less intensely developed volcanic phenomena, as for instance, between
earthquakes, thermal, aqueous, and gaseous springs, mud volcanoes, and the
appearance of bell-formed or dome-shaped trachytic rocks without openings;
the opening of these rocks, or of the elevated beds of basalt, as
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craters of elevation; and, lastly, the elevation of a permanent volcano in
the crater of elevation, or among the 'debris' of its earlier formation. At
different periods, and in different degrees of activity and force, the
permanent volcanoes emit steam acids, luminous scoriae, or, when the
resistance can be overcome, narrow, band-like streams of molten earths.
Elastic vapors sometimes elevate either separate portions of the earth's
crust into dome-shaped unopened masses of feldspathic trachyte and dolerite
(as in Puy de Dome and Chimborazo), in consequence of some great or local
manifestation of force in the interior of our planet, or the upheaved strata
are broken through and curved in such a manner as to form a steep rocky
ledge on the opposite inner side, which then constitutes the inclosure of a
crater of elevation.
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