1866.] On the Antiquity of the Volcanos of Auvergne. 215 
If this theory be adopted, we are precluded, of course, in this 
instance, from appealing to the great depth of the valley, at the 
bottom of which the Baths stand, as indicative of the time required 
for eating so deeply into the substance of the volcanic rocks which 
bound it; but other proofs of great antiquity are not wanting, such 
as the existence of conglomerates consisting of rolled pebbles, which 
underlie one volcanic bed and which support another, as well as of 
tuffs containing fragments of the trachyte and basalt of the neigh- 
bourhood. 
In some places, also, as in the Department of Cantal, fragments of 
limestone containing impressions of plants are scattered through these 
trachytic conglomerates. 
And it would be a bold thing to maintain that, whatever my 
have been the case with the particular valley a'luded to, none of the 
others which score the sides of the volcanic tableland have been due 
to the action of water, or even that such as have been originally 
produced by upheavement were not subsequently modified by denud- 
ing agents. 
In short, the same arguments which induce geologists to assign 
a very long duration to those operations of nature which have in 
other countries scooped out the valleys and moulded into its present 
form the earth’s surface, apply equally to the case of that more 
ancient volcanic region in Central France which has been just 
alluded to. 
Everything therefore concurs to bespeak a high antiquity for 
these formations, and to indicate a long-continued operation of 
denuding forces upon the beds of igneous matter since their 
eruption ; and yet all these events must have been posterior to the 
formation of some at least of the fresh-water beds of the Auvergne 
country, formations which Sir Charles Lyell refers to the Eocene 
period, still a portion of the Tertiary or of the youngest Member of 
the great Family of rocks. 
It seems indeed most probable, that these eruptions of igneous 
matter had broken out at the time when the district was covered by 
extensive sheets of fresh water, like the great lakes of North America, 
and hence may have been derived their greater compactness, as 
‘compared with the more modern volcanic products before alluded to, 
an indication of their having been erupted under a pressure greater 
than that of the atmosphere. And yet, when we recollect that in the 
Eocene period about 34 per cent. of existing species of mollusca 
were already in being, whereas in the newest of the subjacent secon- 
dary rocks no one living form has been as yet detected, and when 
we consider, moreover, how many distinct races of animals and of 
plants, all of which have passed away, succeeded each other in periods 
antecedent to the first dawn of the Tertiary epoch, it must be 
admitted, that vast as was the time occupied in bringing about the 
VOL. III. Q 
