[ 3 ^ ] 
are partly in an original ftate within, and partly increafed 
by new and adventitious materials fuperadded to their 
furface by fucceffive eruptions ; as feems to be the cafe 
of the vulcanic mountains of the Andes, mount Vefuvius, 
and probably of moft other volcanos of any great height ; 
more efpecially where they form parts of continued 
chains. And if fo few of the extincl vulcanic mountains 
appep.r to have been thrown up, from below the com- 
mon furface of the earth, like the Monte di Cenere, See. 
nor even thofe intirely which manifeft adlual volcanos ; it 
feems highly improbable, that other common mountains 
fhould have had fuch an origin ; as many refpeclable wri- 
ters <''>’have been inclined to think ; and hill more fo, that 
fuch fliould have been the foie origin of all mountains ; as 
a late Italian writer on the theory of the earth has very 
unfuccefs fully endeavoured to prove. It alfo plainly ap- 
pears, if I miftake not, from what has been before faid, 
that the phaenomenaof recent volcanos are very little cal- 
culated to give us much inflrudlion about the more cu- 
rious igneous concretions, and the origin of vulcanic 
mountains in general ; and that a few days tout' in fuch 
countries as Auvergne, Velay, and the Venetian ftate are 
worth a feven years apprenticefliip at the foot of mount 
Vefuvius or riEtna; where nothing but a heap of un- 
inflmctive ruins, and a famenefs of j^haenomena appear. 
And lince our ideas, concerning vulcanic effects, have 
(i) Hooke’s Philo fophi^'a! DlfcOurfe on Earthquakes in his pofthumous 
Works, ray’s Phyfiologlcal Difeourfe. raspe Specimen Globi Terraquei. 
j'/f ) MORO de Croftacei che fu i Monti li trovano. 
been 
