34 PROFESSOR FORBES ON THE VOLCANIC GEOLOGY OF THE VIVARAIS. 
Aysac is very perfect, with a nearly circular crater, which rises to a height of 2640 
feet above the sea, and 1257 above the bridge across the Volane at Antraigues. The 
crater is extremely well formed, and I estimated its circumference at about a 
mile. It is broken down at one point only, on the NW. side, by which the lava 
stream has run down the steep face of the hill opposite to the hamlet of Aysac, 
where it enters the bed of the torrent, forming a prismatic mass exactly at the foot of 
the cone. It is from this point that the view of La Coupe, in Fausas’s work, is 
taken, and the general features are exact enough. It is therefore without reason 
that Mr Scrore has charged him with a gross and absurd blunder in representing 
the crater in a direction whence it could not possibly be seen. Mr ScrorE supposes 
the basalts in the foreground to be those which he has himself figured in the 
ravine opposite Antraigues; whereas the view of Fausas is entirely confined to the 
little lateral valley leading to the Collet d’Aysac, as clearly appears from his 
ample, and generally accurate description.* 
The lava of Aysac, after filling up in great part the basin of Antraigues, has 
followed the course of the Volane for several miles, as the numerous basaltic 
patches between that village and Vals sufficiently attest. These basalts are per- 
haps equalled by none in the Vivarais, or in any other part of Europe, as regards 
the exquisite perfection of the pillars of which they are composed ; which, though 
they attain no great height, as at Jaujac and Thuez, are symmetrically polygonal, 
small in diameter, and beautifully jointed, affording beautiful cabinet specimens, 
particularly at the bridge across the Volane, two miles above Vals. This lava, 
like that of Burzet, appears to have been very fluid, and to have accumulated in the 
gorges toa greater height than it could afterwards retain. We find it, accordingly, 
applied in thin sheets upon the steep granite walls of the valley, forming, as usual, 
pillars perpendicular to the cooling surface, as in fig. 2 of Plate V. 
Before finally quitting Antraigues, I must mention that the summit of the 
hill, a little to the ESE. of the village, is occupied by a formation of basalt (which 
is indicated in the map as a lava), but which appears rather to belong to the an- 
cient basalts of the Coyrans and Mesilhac. It is composed chiefly of loose masses, 
excessively hard and heavy, containing olivine, chalcedony, and other substances, 
and decomposing into an earthy matter. It gives no indication of having flowed 
into the valley, and was probably formed before the valleys existed. 
The village of Vals is pleasantly situated on the river Volane, below the last 
traces of the lava of Aysac, and not far from the junction of the gneiss with the 
secondary rocks. Two mineral springs issue from the gneiss at the river's side, 
having temperatures of 59°5 and 61°. They are charged with carbonic acid, and 
contain a little iron and soda. They are frequented in summer by visitors even 
from a considerable distance, and, in consequence, the inn or hétel at Vals is the 
only tolerable one in the whole district, and, as such, will be duly estimated by 
* Recherches, p. 296-298. 

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