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The fresh water limestone, where it is
quarried above the village of Bomagnat, is
very regularly interstratified with thin beds
of argillaceous stone, and is nearly horizontal.
The first day I was there, I discovered
in two of the beds several bones, which, as
I have before stated, are similar in appearance
to those in the Paris basin, and
evidently belong to similar genera of mammalia.
The men told me that the galleries
cut in the limestone were carried to the
distance of one-third of a league under
Gergovia ; but on my second visit, I procured
candles, and penetrated as far as it
had been worked, which I found to be but
a very short distance from the entrance.
I have before expressed some doubt
whether the limestone passes under Gergovia,
or is merely covered to a certain
extent by tuffa which has fallen upon it.
Appearances are in favour of the former
opinion, as the limestone may be traced
nearly round the hill. The basalt which
covers this mountain was once connected
with a larger bed of b a sa lt: this cannot be
doubted ; nor would its separation by the
action of water be more remarkable than
that of the insulated caps of sandstone or
limestone on some of our English mountains,
provincially called Hummocks, which
are evidently the remaining portions of a
large stratum that has been cut through either
by the continued action of water-courses, or
by some sudden and mighty deluge, that
has swept over the globe, and furrowed
its surface into valleys. In Auvergne,
however, where the agency of another
cause, volcanic fire, is clearly apparent in an
extent o f many hundred square miles, we
may doubt whether many o f the isolated
masses of basalt on the summits of the
mountains have not been detached by
the subsidence or partial elevation of
the ground, during the great convulsions
which it has experienced. An accurate
survey of the country, with correct sections
through different parts, and occasional
excavations below the surface, is wanting
to complete our knowledge o f the geology
o f this country, particularly o f certain
interesting positions, which I shall mention
in the following chapter.
It may be useful to recall the attention
of the reader to the geological position o f
the mountains mentioned or described in
the present chapter, by a reference to the
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