324 PUY DE LA POIX.
This I conceive to be the true cause o f
what has excited so much surprise in the
former mountain ; namely that it should so
decidedly present the proofs of the intense
action of fire on its summit, without the
appearance of a regular crater.
I have already mentioned the volcanic
tuffa at the Pont du Chateau ; it is, I believe,
considerably distant from any other
volcanic rock. Of those which I examined,
the nearest to it is the Puy de la Poix,
about three miles east of Clermont, and
about four miles from Pont du Chateau.
The Puy de la Poix is a small hill abounding
in bitumen, or mineral pitch, from
whence it takes its name. The bitumen, in
warm weather, is constantly oozing from it,
forming a current on the northern side,
several yards broad. This hill does not rise
more than fifty feet above the level of the
plain or valley of Clermont, and is distant
about one mile from a larger conical hill,
composed nearly of the same substance,
called the Puy de Cruelle. The occurrence
of volcanic tuffa, in what are called the
older volcanic rocks, at the bottom of the
present valley of Clermont, proves that
the valley or plain was excavated prior to
PtTY DE LA POIX.
the deposition o f the tiiffa ,-^ a fact which
is riot gerierally admitted. The Puy de la
Poix, and the Puy de Cruelle, of which I
shall afterwards speak, are probably the
Remains o f a vast bed of tuffa, that has
once filled up the valley o f Clermont, either
wholly or partially, to a great height. It
would be difficult to explain the cause ot
the permanent transudation of so great a
quantity of bitumen as that which flows
from the small hill of the Puy de la Poix,
unless we suppose it to be connected with
some deep or distant source of that mineral;
for we iire warranted in supposing
the tuffa to be several thousand years old,
and its stock of bitumen must have been
long since exhausted in the Puy d e la Poix,
unless it had been constantly renovated.
In the more recent lavas of Auvergne, I
believe there is no trace of bitumen. Among
the minerals at the Puy de la Poix, I found,
\
Scoriaceous lava.
Chalcedony with asphalt.
Basaltic hornblende.
Whitish phonolite.
Darker ditto, passing into basalt
Ditto, passing into pitchstone,
Stllbite.
Y 3