ve years_, so that a great emigration of the inhabitants
became necessary.

_Their linear direction._--As to the height of the new cones, Von Buch
was assured that the formerly great and flourishing St. Catalina lay
buried under hills 400 feet in height; and he observes that the most
elevated cone of the series rose 600 feet above its base, and 1378 feet
above the sea, and that several others were nearly as high. The new
vents were all arranged _in one line_, about two geographical miles
long, and in a direction nearly east and west. If we admit the
probability of Von Buch's conjecture, that these vents opened along the
line of a cleft, it seems necessary to suppose that this subterranean
fissure was only prolonged upwards to the surface by degrees, and that
the rent was narrow at first, as is usually the case with fissures
caused by earthquakes. Lava and elastic fluids might escape from some
point on the rent where there was least resistance, till, the first
aperture becoming obstructed by ejections and the consolidation of lava,
other orifices burst open in succession along the line of the original
fissure. Von Buch found that each crater was lowest on that side on
which lava had issued; but some craters were not breached, and were
without any lava streams. In one of these were open fissures, out of
which hot vapors rose, which in 1815 raised the thermometer to 145 degrees
Fahrenheit, and was probably at the boiling point lower down. The
exhalations seemed to consist of aqueous vapor; yet they could not be
pure steam, for the crevices were incrusted on either side by siliceous
sinter (an opal-like hydrate of silica of a white color), which extended
almost to the middle. This important fact attests the length of time
during which chemical processes continue after eruptions, and how open
fissures may be filled up laterally by mineral matter, sublimed from
volcanic exhalations. The lavas of this eruption covered nearly a third
of the whole island, often forming on slightly inclined planes great
horizontal sheets several square leagues in area, resembling very much
the basaltic platforms of Auvergne.

_Pretended distinction between ancient and modern lavas._--One of the
new lavas was observed to contain masses of olivine of an olive-green
color, resembling those which occur in one of the lavas of the Vivarais.
Von Buch supposes the great crystals of olivine to have been derived
from a previously existing basalt melted up