292 Profefor WiuLtams on. Eartbquakes. 
And thefe are phenomena in all refpe&ts. agreeing with thole 
that have attended the earthquakes of this country. 
The ftrength and force of fuch a vapour, would be fufficient 
to. account for the violence of any fhocks we have had. A very 
great force muft be requifite to heave up, and caufe a progreflive 
fwell in. the furface of the.carth, and this, perhaps, from fome: 
depth below.—And with what ferce fubterraneous vapours may 
be attended, we may form. fome idea from their. effects... In. 
common thing to fee them throw up at ence, fuch clouds of 
fand; afhes and pumice-ftones, as are capable cf. darkening the. 
whole air, and'covering the neighbouring country with a fhower 
of duft, &c. to many miles diftance. Great ftones, alío, of 
fome tons weight, are often thrown tothe diftance of two. or 
three miles, by fuch explofions. Monf. Bouguer tells us, that 
“ he met with ftones in South-America, of eight or nine feet 
diameter, that had been thrown from the volcano Catopaxi, by 
one of thefe blafts, to the diftance of more than three leagues." 
In Ulla's account, the whole plain, near Latacunga, is faid to: 
be full of pieces of rocks, fome of which. were thrown, from 
the fame volcano, to.the diftance of five leagues.-- If fubter-- 
rancous vapours, when they have had nothing to confine them,. 
have acted with fuch force, we may eafily conceive that they - 
muft heave up, and caufe a progreflive: fwell in the furface o£ 
the earth, when their force was confined, and their motion di- 
seéted by a particular paffage. 
The eruptions and effufons that haveattended our earthquakes, 
have alfo borne. ftrong marks of fubterraneous vapour.. "Phat: 
* vapour of Sufficient force to fhake and move the furface of a: 
: 3 whole 
$ Phil. Tranh. for 1760, p. 5932; 
