[ 576 ] 
Sect. II. 
23. How well foever thefe fads may agree with 
the fuppofition before laid down, That lubterraneous 
fires are the caufc of earthquakes, one doubt, how- 
ever, may perhaps remain ; viz. how it is poffiblc 
that fires fhould fubfift, winch have no communica- 
tion with the outward air ? I11 anfwer to this, I 
might alledge the example of green plants, which take 
fire by fermentation, when laid together in heaps ; 
where the ad million of the outward air is fo far from 
being necefiary, that it will effectually prevent their 
doing fo. But, to pafs by this, we have many in- 
ftances more immediately to the purpofe. 
24. It can hardly be fuppofed, that the fires of the 
generality of volcanos receive any fupply of frelh air 
(for this muft effectually be prevented by that vapour, 
which is continually rufhing out at all their vents), 
and yet they fubfift, and frequently even increafe, for 
many ages. Now, thefe are fires of the very fame 
kind with thofe, which I fuppofe to be the caufe 
of earthquakes. Other fads, ftill more exprefly to 
the purpofe, are as follow: 
ay. In the earthquake of the ift of November 
1 755, we are told, that both fmoke and light flames 
were feen on the coaft of Portugal, near Colares ; and 
that, upon occafion of fome of the fucceeding fhocks, 
a flight fmell of fulphur was perceived to accompany 
a “ fog, which came from the fea, from the fame 
“ quarter, whence the fmoke appeared 
* Sec Philof. Tranf. vol. xlix. p.414, &V. 
26. Ill 
