Royal Institute of France. 463 
burnt stones ; and the reverberation of the internal furnaces on 
the vapours which issue, causes this illusion. The lava flows 
very slowly: its edges when cooled form an embankment for it, 
and keep it above the level of the soil, which is covered with 
scoriz ; it is very difficult to get a sight of its fluid parts. We 
know besides, that its heat has nothing in it similar to that of 
glass in fusion; for when it envelops trunks of trees, it does not 
ehar them to the centre. M.de la Groye is also of opinion that 
the lava owes its fluidity to some principle which is consumed 
by the very act of fusion, and to this cireumstance is owing the 
difficulty of fusing again that which has once cooled. The full 
mass, the part not swelled up into scoriz, has a stony aspect : 
this is what the Germans call grausteim. The author compares 
the periods of the fusion of the lavas with those through which 
the salts pass, which fuse after being swelled up. He relates 
some curious facts with respect to the prodigiously long duration 
of their heat, and thence concludes that they bear within them- 
selves the principle of their own heat, and that they do not 
possess a heat simply communicated. To all these remarks 
M. de la Groye adds a very detailed account of the grand erup- 
tion of 1813, which produced an infinity of ashes and small 
stones, but the lava of which did not reach the length of the 
cultivated grounds. 
After having studied with so much care the burning volcanoes, 
M. de la Groye wished also to give an account of the motives 
upon which the opinion is founded, that various mountains 
may be classed among burnt-cut volcanoes; and he visited one 
of them which De Saussure and other great geologists had al- 
ready placed in this class, but with respect to which the obstinate 
Neptunists will still find abundance of pretexts for confirming 
their doubts. 
This mountain was that of Beaulieu, about three leagues from 
Aix in Provence. The inequalities of the soil which surrounds 
it, represent currents similar to those of lava: its extent is 
1200 fathoms by 6 or 700 in breadth: its mean elevation above 
the sea is 200; the surrounding soil is caleareous to an infinite 
distance: towards the east are the basaltic rocks which seem to 
form the nucleus of the whole system, but in the basaltic part 
itself there are also sea-shclls and abundance of limestone. The 
amygdaloids and the basalts are covered with them in several 
places; in others their fragments are incrusted with them, and 
compose with this limestone a sort of brecke. He has often pe- 
netrated into the cells of the amygdaloids. 
Nevertheless the principal rock is the secondary grunstein of 
the Germans composed of feldspar and pyroxene, sometimes in 
such large grains that it resembles granite. It forms a long 
current, 
