MONTPEZAT—LAVA OF CHAMBON. 25 
volcanic products, fills the bed of the stream for a very considerable distance, 
rising with a very steep acclivity, which shews that its viscidity must have been 
considerable to allow it to harden at so great an inclination. M. SErroutL, watch- 
maker at Montpezat, showed me a sapphire and zircon which he had picked up 
near this place, which is interesting from the occurrence of these minerals in the 
lavas of Croustet, near Le Puy. The lava of Le Fau is surmounted by beds of 
volcanic conglomerate, of which the river has made a section in passing between 
it and the granite on the right bank of the valley ; the thickness of the conglome- 
rate is here at least 100 feet, and the inclination may amount to 25°. The vol- 
canic stream presents a very massive and striking appearance, and leads to the 
belief that we are in the immediate neighbourhood of a volcanic focus ; and such 
might be supposed to exist in the steep slopes covered with slag and volcanic con- 
glomerate (the conglomerate still uppermost), which rise to a great height on the 
left bank of the stream, not far from its source. Nothing of the kind, however, 
appears; the beds become thinner, and are in absolute contact at no great depth 
with the granite which constitutes the neighbouring slopes, or with granitic bould- 
ers covering the rock at D, Plate IV., fig. 2. The lava in contact with the granite 
has evidently consolidated in its present position, from the nicety of its adaptation 
to the rock, and from the shortness and fragility of its structure. The position of 
this volcanic cwrtain will be best understood from the plan in the figure just re- 
ferred to, which shews the uppermost part of the valley of Montpezat, as traversed 
by the very steep paved road leading by the hamlet of Le Pal from Usclades and Le 
Puy. This road has since been superseded by a new one, which was nearly com- 
pleted at the time of my last visit. It will be seen that the highly-inclined beds 
D, are those now described, and are divided by a streamlet which issues from a 
kind little circular valley, in which a cottage is marked.* This circus might well 
pass, upon a superficial examination, for the source of the lava or a true crater. 
It has, however, no such pretension, being completely excavated in granite; and 
the aforesaid curtain of lava and breccia forming a thin exterior facing on the side 
exposed to the high road. The height which the volcanic formations attain on 
this slope is no less than 4134 feet above the sea, and nearly 2300 feet above 
Montpezat, though so little distant. It will be understood, therefore, that the 
slope is extremely rapid. 
The place where these remains occur is called Le Chambon: we shall there- 
fore denominate the deposit by the name of the lava of Chambon. It is hoped 
that it has been made evident that no eruption took place in this spot. The ex- 
cavation of the ravine behind D, and the numerous contacts with the granitic soil, 
shew that it is entirely foreign to the place. Whence then is it derived? There 
can be but one answer, even although that conclusion be attended with some diffi- 
* There is also another cottage more to the left, in a place where, on Cassrn1’s Map, is marked 
“Lac de Ferrand ;” that little lake in reality lying higher up in the direction of the volcano of 
Bauzon. 
VOL. XX. PART I. G 
