1866.| On the Antiquety of the Voleanos of Auvergne. 213 
columnar structure are not met with in those parts of the current 
which occupy the slope of the mountain, but only at its termination 
in the valley below, and that even there these characters are 
confined to the lower portions, where the pressure must have been 
greatest, the basalt bemg surmounted by a considerable thickness 
of cellular lava of the usual kind. Moreover, a difference can be 
traced in the degree of its compactness according to the relative 
position which the specimen holds in the basaltic bed, the upper 
layers being the most cellular. 
In the Vivarais, then, as well as in Auvergne, we have abundant 
instances of lava streams, which, although amongst the most recent 
the district affords, being poured forth at a time when the general 
configuration of the country had become nearly what it is at present, 
exhibit, nevertheless, traces of their high antiquity, from having 
been subjected to the long-continued operation of denuding agents, 
Where these agents have been at work their relative date may 
be fixed, but we do not appear to possess the same means of 
referring to a particular epoch the five isolated domes of trachyte 
which occur on the tableland to the west of the city of Clermont, 
although the occurrence of free muriatic acid in one of them would 
imply that they were modern. 
These conical hills, of which the loftiest, called the Puy de Déme, 
rises to the height of 4,842 feet, or 3,554 feet above the level of 
Clermont, seem each to have proceeded out of the midst of a kind of 
erater formed by volcanic rocks of the usual character and appearance, 
and therefore bearing no analogy to the material of which they 
are themselves principally constituted. Their general appearance is 
represented in the annexed woodcut, from a drawing of Scrope’s. 
Fic. 3. 
fi 
They seem to bear some resemblance, although on a much 
larger scale, to the Bosses or Mamelons, to use a French phrase, 
protruding from the midst of the craters of Rocca Monfina, near 
Terracina, and of Astroni, near Naples, which may perhaps be 
paralleled by those dark spots observed by astronomers in the 
midst of the circular hollows existing on the surface of the moon, 
