[ 588 j 
very considerable, it may have a great effect in pro- 
ducing fome of the fingularities of particular earth- 
quakes *► 
PART II. 
5 1 . T N the former part of this effay, I have re- 
counted fome of the principal appearances of 
earthquakes, as well as thofe particulars in the druc- 
ture of the earth, upon which I fuppofe thefe ap- 
pearances to depend. From what has been already 
faid, I think it is fufficiently manifed, that, in fome 
indances at lead:, earthquakes are actually produced 
by fubterraneous fires ; it now, therefore, remains to 
be fhewn, how all the appearances above- recited, as 
well as many other minuter circumdances attending 
earthquakes, may be accounted for from the fame 
caufe. 
Sect. I. 
f 2. The returns of earthquakes in the fame places,, 
either at fmall or large intervals of time, are very 
confident with the caufe affigned : fubterraneous fires, 
from their analogy to volcanos, might reafonably be 
fuppofed to fubfid for many ages, though we had not 
thofe indances *f* already mentioned, which put the 
* Fig. 2. reprefents a feifion of the ftrata trapping down after 
the manner juft defcribed. The fedfion is fuppofed to be made 
perpendicularly to the horizon, and at right angles to the dire&ion 
of the cleft : an inftance of this kind, amongft the coal miners of 
Mendip hi Somerfetfhire, is mentioned in thePhilof. Tranf. See 
the account of it, together with a drawing, in N° 360. or Jones's 
Abr. vol. iv. part ii. p. 260. 
t See art. 28 to 32 inclufive. 
matter 
