Dr j)aubeny mi the Ancient Yolcmiocs of Auvefgm* 531 
philosophers are so fond of seizing upon as evidence of volcanic 
action. I examined the spot myself, and was, I confess, struck 
with the apparently broken condition of the contiguous gra- 
nite, and yet it seems, upon cool consideration^ to be physically 
impossible that a mass of rock of this shape and size should 
have been propelled from the earth, and should have remained 
for ages protruding, in the position in which we now find it. 
I need only appeal to those who have visited the spot, or even 
to such as have examined the plates of M. Faujas, in his large 
work on the Vivarais, in support of this assertion. 
Another instance of apparent change in the stratification of a 
rock, as connected with a dike, occurred to me in the course of 
my tour in Dantal, which, considering all the circumstances, it 
might be rather bold to refer to the operation of a force acting 
from below upwards. It occurs about a league from the town 
of Aurillac, on the road to Murat, in the fresh water formation 
which prevails over much of that part of Cantal, very different, 
indeed, from that around Paris, if we regard its external cha- 
racters, but identified with it by the shells which it contains. 
This calcareous rock is traversed obliquely by a dike of a kind 
of amygdaloidal wacke, containing in its cavities much green 
earth, and inclosing fragments of various trap-rocks, as well as 
of the limestone which it cuts through, and of the flinty nodules 
which the latter contains. Just above the stratification of the 
calcareous rock, it is remarkably changed from an horizontal to a 
vertical direction ; yet, on the other hand, we observe organic 
remains in the limestone, even where it is in immediate contact 
with the dike, and the latter nowise affected in point of hardness 
or other circumstances. Nor does the aspect of the dike itself, 
any more than that of the rock which contains it, favour the 
idea, which its altered stratification naturally suggests. 
In Cantal, the tuff is best displayed near the village of Tey- 
zac, on the road from Aurillac to Murat, where the traveller 
should establish his head-quarters at a very comfortable inn 
which the place affords, as a convenient central position, from 
whence he may examine the Plomb de Cantal, and most of 
the interesting country in the Department. The tuff there, is 
placed between two beds of trachyte, being found rather less 
than half way on^ either side of the hills which bound the valley^, 
