[so] 
ami damp vapours, impregnated with falts, fulphur, 
alum, &c. Where the above-mentioned vapours 
have not operated, the ftrata of pumice and erupted 
matter, that compofe the cone of the Solfaterra, 
are like thofe of ail the high grounds in its neigh- 
bourhood, which I fuppofe to have been thrown up 
likewife by explofion. I have feen here, half of a 
large piece of lava perfedlly calcined, whihl the 
other half out of the reach of the vapours has been 
untouched •, and in fome pieces the center feems to 
be already converted into true marble. 
The variegated fpecimens then, above deferibed, 
are nothing more than pumice and erupted matter, 
after having been adted upon in this manner by the 
hot vapours ; and if you conhder the procefs, as I 
have traced it, from bitumen to pumice, and from 
pumice to marble, you will think with me that it is 
difficult to determine the primitive date of the many 
wonderful produdfions we fee in nature. 
I found in the tufa of the mountain of Paufilipo, 
a fragment of lava: one fide I polifbed, to ffiew 
it to be true lava j the other ffiews the figns of 
the tufay with which it is incorporated. It has evi- 
dently been rounded by fridlion, and mod probably 
by rolling in the fea. Is it not natural then to ima- 
sine that there mull have been volcanoes near this 
fpot, long before the formation of the mountain of 
Paufilipo ? This little ftone may perhaps raife in your 
mind fuch refiedlions, as it did in mine, relative to 
the great changes our globe fuifers, and the proba- 
bility of its great antiquity. 
III. A 
