Dr Dauberiy 07i the Volcarwcs of Awvergne. 
gether with the regularly conical form of the Puy de Dome, 
and other of the hills alluded to, will prevent our adopting the 
former opinion, and incline us, in preference, to the theory of 
Von Buch, which is, moreover, favoured by the circumstance of 
these hills being, for the most part, situated as it were in a cra- 
ter, in the midst of rocks which possess every mark of having 
been the seat of volcanic action. 
From what materials this singular rock can have been produ- 
ced, seems still more problematical ; if, as is most probable, from 
the subjacent granite, what is become of the greater part of the 
quartz, which forms so essential and abundant an ingredient in 
the latter rock ? why has a heat, capable of dissipating so large a 
portion of this refractory material, and of reducing the felspar 
to an harsh and often pulverulent form, left the crystals of au- 
gite untouched, and apparently effected no alteration in the mi- 
ca ? These are questions, whichj in the present state of our 
knowledge, it would be difficult to answer, although, it should 
be remarked, that, in estimating the amount of the quartz dissi- 
pated, we should do wrong to calculate it from the difference 
between the quantity of that mineral existing in the granite 
and in the domite ; but must deduce it from a comparison of 
the quantity of silex that would be contained in the quartz we 
suppose to have disappeared, and that existing in the felspar 
substituted. Now, as felspar contains from 55 to 70 pe?' cent. 
of silex, and quartz frequently not more than 9^ per cent, the 
real difference between the constitution of the two rocks is con- 
siderably less than might be at first supposed. With regard to 
the crystals of augite, these, probably, are rather the results of 
the igneous action, than the unaltered relics of the original 
stratum. On the other hand, it is impossible to return from 
viewing the Puy Chopine without feeling a persuasion, that the 
granite and domites there seen associated, are, in a certain de- 
gree, connected wdth each other, and that, in all probability, the 
latter has been formed by the agency of heat, modified by pe- 
culiar circumstances, out of the materials of the former. Adopt- 
ing this theory, therefore, as the most probable that has been 
offered, we may account for the intermixture of the hornblende 
rock, by supposing tliat it formed beds in the granite which 
was thrown up, whilst the unequal operation of heat may cx=* 
