7G 
STRATA OF LATA. 
as the volcanic phenomena themselves ; and in order to raise 
ourselves to geological conceptions worthy of the greatness 
of nature, we must set aside the idea that all volcanoes are 
formed after the model of Vesuvius, Stromboli, and Etna. 
The external edges of the Caldera are almost perpendi- 
cular. Their appearance is somewhat like the Sornma, seen 
from the Atrio dei Cavalli. We descended to the bottom 
of the crater on a train of broken lava, from the eastern 
breach of the enclosure. The heat was perceptible only in 
a few crevices, which gave vent to aqueous vapours with a 
peculiar buzzing noise. Some of these funnels or crevices 
are on the outside of the enclosure, on the external brink of 
the parapet that surrounds the crater. We plunged the 
thermometer into them, and saw it rise rapidly to GS and 75 
degrees. It no doubt indicated a higher temperature, but 
we could not observe the instrument till we bad drawn it up, 
lest we should burn our hands. M. Oordier found several 
crevices, the heat of which was that of boiling water. It 
might be thought that these vapours, which are emitted in 
gusts, contain muriatic or sulphurous acid ; but when con- 
densed, they have no particular taste; and experiments, 
which have been made with re-agents, prove that the chim- 
neys of the peak exhale only pure water. This phenomenon, 
analogous to that which I observed in the crater of Jorullo, 
deserves the more attention, as muriatic acid abounds in the 
greater part of volcanoes, and as M. Vauquelin has dis- 
covered it even in the porphyritic lavas of Sarcouy in 
Auvergne. 
I sketched on the spot a view of the interior edge of the 
crater, as it presented itself in the descent by the eastern 
break. Nothing is more striking than the manner in which 
these strata of lava arc piled on one another, exhibiting the 
sinuosities of the calcareous rock of the higher Alps. These 
enormous ledges, sometimes horizontal, sometimes inclined 
and undulating, are indicative of the ancient fluidity of the 
whole mass, and of the combination of several deranging 
causes, which have determined the direction of each flow. 
The top of the circular wall exhibits those curious ramifica- 
tions which we find in coke. The northern edge is most 
“levated. Towards the south-west the enclosure is consider- 
ably sunk, and an enormous mass of scorious lava seems 
