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above the village of Volvic, may be from
300 to 400 yards, but it spreads out much
wider below. The stone near the surface
is rough and cellular; a few feet below, it
becomes apparently compact, but is full of
very minute pores. In many parts the lava
contains laminse of specular iron ore in
great abundance ; it contains also irregular
nodules, and plates of quartz : its colour is
a very dark grey, and its general appearance
is exactly similar to some of the
modern dark grey lavas from Vesuvius.
The stone divides into irregular prisms,
which are raised for building-stone ; it is
almost the only stone employed for the
purpose in this part of France, and is both
light and durable. There is another use to
which it has been recently applied ; it is cut
into pieces, from five to eight feet in length,
and about one foot in diameter, which are
bored for water pipes, and sent to Paris.
Its extreme hardness, tenacity, and durability,
render it well suited to this purpose,
the pores being too minute to admit the
escape of water.
We ascended more than a mile along the
side of a granitic mountain : the road runs
for a considerable distance immediately
above the lava, but in some parts comes
close to it, and I could place one foot on the
bare granite, and the other upon the side of
the current o f lava. I was desirous to see the
effect of the contact, and what change was
produced in the granite by its proximity to
such a mass of volcanic matter in fusion ;
but its surface was so much decomposed,
that it would require a deep excavation to
be made, to ascertain whether the granite
had been partially fused, or in any degree
affected by heat.
In ascending the valley, and observing
the granitic rocks on each side o f it, and
the dark mass of stone filling up the bottom,
it would scarcely be possible for any
one, however unacquainted with geological
phenomena, to avoid inquiring how the
latter came to be thrown between rocks so
dissimilar to it in appearance. Higher up
there is an insulated hill of granite, surrounded
by lav a : it is evident that this hill
had opposed a barrier to the descending current,
until the lava accumulated to a considerable
height, and divided in two streams,
which united again below.
When we had arrived at the elevated
plain above the valley, we turned to the
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