96
or by an interior shake which shook and reversed the basis on
which it was built up; a shake which nevertheless was not
strong enough to produce any excretion outside and to dis-
turb the higher layer of the mineral substances. These shakes
in the interior of the volcanoes, able to half-open the ground,
are felt mainly when the usual air windows are closed, any
more free exit remains for the gaseous substances, which are
expanded by heat. I assign this cause to the formation of the
lake Pavin that everything confi rms that it is not a crater of a
volcano^2 ; as Mr. de Montlosier noted very well: it appears to
(^2) It does not allow any evidence of lava fl ow, which it would have given
birth, to be seen: the basalt of the edge is not its product. However such
be open under a vast basaltic lava fl ow. It is noteworthy that
the lava side preserves their natural position, which would
not be the case if the opening of this lake was due to a strong
explosion, which would have expelled the volcanic material
an immense mouth implies widespread excretions, the quantities of
which are related to the size of the crater –as no scoriae are visible on
its edges. – Some kind of bench prevails around it whose formation,
either appears impossible to explain if one assumes that it had been a
crater or, on the contrary, an easy explanation consists in admitting that
it owes its origin to an accidental explosion of a volcano: one sees that
not only the part of the lava fl ow, which corresponded to the pit which
opened, probably detached from the mass, but also the neighbouring
lava parts. ”
Fig. 5.3 “ Vue du lac Pavin prise des Rampans des Monts d’Or, près de
Vassivière dans la direction du Nord Ouest à l’Est Sud. Le Cratère sur
lequel sont contenues les Eaux se marie avec la masse d’un ancien vol-
can qui porte le nom de puy Montchal. A sa cime on retrouve encore les
formes émoussées d’un cratère détruit. Le bord du Cratère qui renferme
les eaux du lac ont cent vingt pieds d’élévation à partir du niveau de
l’Eau qui s’enfonce jusqu’à 288 pieds au dessous. Une source très abon-
dante coule de dessous un courant de Basalte de 47 pieds d’épaisseur.
On l’aperçoit à la face intérieure du Rebord qui fait face au spectateur
auprès du Puy Montchal / Lake Pavin as seen from Rampans of the Monts
d’Or near Vassivière from northwest to east- southeast. The Crater in
which Waters are contained does harmonize with the mass of an old
volcano that bears the name of puy Montchal. On its summit one still
fi nds the blunted shape of an eroded crater. The rim of the Crater which
contains water of the lake is hundred and twenty feet in height above the
water level, which sinks down to 288 feet below. A very abundant spring
pours from the bottom of a basaltic current 47 feet thick. One sees it at
the interior face of the Edge that faces the spectator near the Puy
Montchal “. Watercolour board 36 of Delécluze’s album and notes
( 1821 ). The detailed analysis of the drawing and its comparison with the
digital elevation model of the present ground surface shows that the art-
ist deliberately lowered the edge of the crater to make the lake visible
P. Boivin and S. Jouhannel
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