258 
EOCENE PERIOD. 
[Ch. XIX, 
of the period under consideration, and shall then proceed to 
show that there are in the same country volcanic rocks of 
much newer date, some of which appear to be referrible to the 
Miocene era. 
Volcanic rocks associated ivith Lacustrine inAuvergne. — The 
first locality to which we shall call the reader's attention is Pont 
du Chateau near Clermont, where a section is seen in a preci- 
pice on the right bank of the river Allier *. Beds of volcanic tuff 
alternate with a fresh-water limestone, which is in some places 
pure, but in others spotted with fragments of volcanic matter, 
as if it were deposited while showers of sand and scorias were 
projected from a neighbouring vent f- This limestone contains 
the Helix llamondi and other shells of Eocene species. It is 
immaterial to our present argument whether the volcanic sand 
was showered down from above, or drifted to the spot by a 
river, for the latter opinion must presuppose the country to 
have been covered with volcanic ejections during the Eocene 
period. 
Another example occurs in the Puy de Marmont, near 
Veyres, where a fresh-water marl alternates with volcanic tuff 
containing Eocene shells. The tuff or breccia in this locality 
is precisely such as is known to result from volcanic ashes 
falling into water, and subsiding together with ejected frag- 
ments of marl and other stratified rocks. These tuffs and 
marls are highly inclined, and traversed by a thick vein of 
basalt which, as it rises in the hill, divides into two branches. 
Gergovia. — The hill of Gergovia near Clermont affords a 
third example. We agree with MM. Dufrenoy and Jobert 
that there is no alternation here of lava and fresh-water strata, 
in the manner supposed by some other observers J; but the 
position and contents of some of the tuffs prove them to have 
been derived from volcanic eruptions which occurred during 
the deposition of the Eocene formations. 
* This place, and all the others in Auvergne, mentioned in this chapter, were 
examined by the author, in company with Mr. Murchison, in 1828. 
f See Scrope's Central France, p, 21, + Scrope ; ibid. p. 7. 
