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A better idea of the relative position of
the rocks of this district may be obtained
from the annexed cut, representing a section
of the country, from the plain of the
Allier, to the volcanic rocks west of Clermont.
As no section, that I know of, has
hitherto been published, I trust that both
this and the following outlines, will be
found interesting to the geological reader.
The section is taken in the direction from
east to west. The lowest rock, or granite,
A. A, is a continuation of the granite ot
the Forez mountains. B. B represents the
fresh-water limestone in the valley of Clermont
; the strata are nearly horizontal.
C. C. C. C are beds of volcanic tuffa, intermixed
with bitumen. D. D. D, basalt,
capping the tuffa in various parts. There
is also basalt in some of the valleys, for the
currents of lava pass into basalt. F , a
dome-shaped hill of trachyte ; whether this
be a part of the granite melted and forced
up, or the remains of a bed oi felspathic
lava, is undecided ; the nature of the rock
H, immediately under the trachyte mountains,
is not ascertained. F. F, volcanic
mountains with craters, rising among the
other mountains ; from many of these.
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