Some geologists had erroneously supposed, from observations made on recent cones
of eruption, that lava which consolidates on steep slopes is always of a
scoriaceous or vesicular structure, and never of that compact texture which we
find in those rocks which are usually termed "trappean." Misled by this theory,
they have gone so far as to believe that if melted matter has originally
descended a slope at an angle exceeding four or five degrees, it never, on
cooling, acquires a stony compact texture. Consequently, whenever they found in
a volcanic mountain sheets of stony materials inclined at angles of from 5
degrees to 20 degrees or even more than 30 degrees, they thought themselves
warranted in assuming that such rocks had been originally horizontal, or very
slightly inclined, and had acquired their high inclination by subsequent
upheaval. To such dome-shaped mountains with a cavity in the middle, and with
the inclined beds having what was called a quaquaversal dip or a slope outward
on all sides, they gave the name of "Elevation craters."
As the late Leopold Von Buch, the author of this theory, had selected the Isle
of Palma, one of the Canaries, as a typical illustration of this form of
volcanic mountain, I visited that island in 1854, in company with my friend Mr.
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