262 
EOCENE PERIOD. 
[Ch. XIX. 
crater of Etna, it may have formed an insignificant feature in 
the great pile, and may frequently have been destroyed and 
renovated. 
We cannot at present determine the age of the great mass 
of Mont Dor, because no organic remains have yet been found 
in the tuffs, except impressions of the leaves of trees of species 
not determined. Some of the lowest parts of the great 
mass are formed of white pumiceous tuffs, in which animal 
remains may perhaps be one day found. In the mean time, 
we conclude that Mont Dor had no existence when the grits 
and conglomerates of the Limagne, which contain no volcanic 
materials, were formed ; but some of the earliest eruptions 
may perhaps have been contemporary with those described in 
the commencement of this chapter. To the latest of these 
eruptions, on the other hand, we refer those trachytic breccias 
of Mont Perrier which were shown in the sixteenth chapter, p. 
217, to alternate with Miocene alluviums. 
Velay. — The observations of M. Bertrand de Doue have not 
yet established that any of the most ancient volcanos of Velay 
were in action during the Eocene period, although it is very 
probable that some of them may have been contemporaneous 
with the oldest of the Auvergne lavas. There are beds of 
gravel in Velay, as in Auvergne, covered by lava at different 
heights above the channels of the existing rivers. In the 
highest and most ancient of these alluviums the pebbles are 
exclusively of granitic rocks; but in the newer, which are 
found at lower levels, they contain an intermixture of volcanic 
substances. We have already shown, in the sixteenth chapter, 
that, in the volcanic ejections and alluviums covered by the 
lavas of Velay, the bones of animals of Miocene species have 
been found, in which respect the phenomena accord perfectly 
with those of Auvergne. 
Plomb du Cantal. — In regard to the age of the igneous 
rocks of the Cantal we are still less informed, and at present 
can merely affirm that they overlie the Eocene lacustrine strata 
of that country. The Plomb du Cantal (see Map, wood-cut 
