n that there is almost conclusive evidence that man
was a witness to the later volcanic outbursts of the Vivarais, and as
these craters seem to be of somewhat earlier date than those of the Puy
de Dome group, we cannot doubt that they were in active eruption when
human beings inhabited the country, and not improbably within what is
known as the _Historic Period_. No mention, however, is made either by
Caesar, Pliny, or other Roman writers of the existence of active
volcanoes in this region. Caesar, who was a close observer, and who
carried the Roman arms into Auvergne, makes no mention of such; nor yet
does the elder Pliny, who enumerated the known burning mountains of his
day all over the Roman Empire. It is not till we come down to the fifth
century of our era that we find any notices which might lead us to infer
the existence of volcanic action in Central France. This is the
well-known letter written by Sidonius Apollonarius, bishop of Auvergne,
to Alcinus Avitus, bishop of Vienne, in which the former refers to
certain terrific terrestrial manifestations which had occurred in the
diocese of the latter. But, as Dr. Daubeny observes, this is no evidence
of volcanic action in Auvergne, where Sidonius himself resided; the
terrestrial disturbances above referred to may have been earthquake
shocks of extreme severity.[11]

But although we have no reliably historical record of volcanic action
amongst the mountains of the Mont Dome group, the fact that these are,
comparatively, extremely recent will be evident to an observer visiting
this district, and this conclusion is based on three principal grounds:
first, because of the well-preserved forms of the original craters,
though generally composed of very loose material, such as ashes,
lapilli, and slag; secondly, because of the freshness of the
lava-streams over whose rugged surfaces even a scanty herbage has in
some places scarcely found a footing;[12] and thirdly, because the lava
from the crater-cones has invaded channels previously occupied by the
earlier lavas, or those which had been eroded since the overflow of the
great basaltic sheets of Mont Dore. Still, as in the case of the valleys
of Lake Aidot, of Channonat, and of Royat, these streams are
sufficiently ancient to have given time for the existing rivers to have
worn out in them channels of some depth, but bearing no comparison to
the great valleys which had been eroded out of the more ancient lavas,
such as thos