rated by excessive rainfall during the
succeeding Post-Pliocene and Pluvial periods, was continued until plains
and extensive river-valleys were eroded out of the sheets of lava and
their supporting granitic rocks and the adjoining lacustrine strata.

_4th Stage._--A new outburst of volcanic forces marks this stage, during
which the chain of the Puy de Dome was thrown up on the west, and that
of the newer cones of the Vivarais on the south-east of the lacustrine
tract. The waters of the lake were now completely drained away through
the channel of the Allier, and denudation, extending down to the present
day, began over the area now forming the Vale of Clermont and adjoining
districts. The volcanic action ultimately spent its force; and somewhere
about the time of the appearance of man, the mammoth, rhinoceros, stag,
and reindeer on the scene, eruptions entirely ceased, and gradually the
region assumed those conditions of repose by which it is now physically
characterised.

[1] The literature referring to this region is very extensive. Guettard
in 1775, afterwards Faujas, published descriptions of the rocks of the
Vivarais and Velay; and Desmarest's geological map, published in 1779,
is a work of great merit. The district was afterwards described by
Daubeny, Lyell, Von Buch, and others; but by far the most complete work
is that of Scrope, entitled _Volcanoes of Central France_, containing
maps and numerous illustrations, published in 1826, and republished in a
more extended form in 1858; to this I am largely indebted.

[2] A monument to Pascal, erected by the citizens, occupies the centre
of the square in Clermont. It will be remembered that Pascal verified
the conclusions arrived at by Torricelli regarding the pressure of the
atmosphere, by carrying a Torricellian tube to the summit of the Puy de
Dome, and recording how the mercury continually fell during the ascent,
and rose as he descended. This experiment was made in 1645.

[3] In this visit to Auvergne in the summer of 1880, the author was
accompanied by his son, Dr. E. Gordon Hull, and Sir Robert S. Ball. On
reaching the station at the summit of the ridge it seemed as if the
volcanic fires had again been lighted, for the whole sky was aglow with
the rays of the western sun.

[4] On the other hand, certain beds of ash and other volcanic _ejecta_
occur in _the uppermost_ strata of lake deposits of Limagne, so that
these may indicate the commencement of the period