upon the Phenomena, of Earthquakes. 331 
78. If, then, the largest fires are to be supposed to subsist 
under the ocean, it is no wonder that the most extensive earth- 
quakes should take their rise from thence: the great earthquake 
of Lisbon has been shown to have done so*; and that the cause 
of it was also at a greater depth, than that of many others, ap- 
pears from the greater velocity with which it was propagated +. 
79. The great earthquake that destroyed Lima and Callao in 
1746, seems also to have come from the sea; for several of the 
ports upon the coast were overwhelmed by a great wave, which 
did not arrive till four or five minutes after the earthquake began, 
and which was preceded by a retreat of the waters{, as well as 
that at Lisbon. Against this, it may, perhaps, be alleged, that 
there were four volcanos broke out suddenly §, in the neighbouring 
mountains, when this earthquake happened, and that the fires 
of these might be the occasion of it. This however, | think, is 
not very probable; for, to omit the argument of the wave, and 
previous retreat of the waters, already mentioned, it is not very 
likely, that more than one fire was concerned: besides, the va- 
pour, opening itself a passage at these places, could not well be 
supposed, if it took its rise from thence, to spread itself far; 
especially towards the sea, where it is manifest, that the strata 
over it were of great thickness, as appears from the great velo- 
city with which the earthquake was propagated there: the shocks 
also continued with equal, or nearly equal violence, for some 
months after the openings were made; whereas, if these fires 
had been the cause of them, tliey must immediately have ceased, 
upon the fires finding a vent, as it has happened in other cases ||. 
It is therefore much more probable, that a very large quantity 
of vapour, taking its rise from some far more extensive fire un- 
der the sea, spread itself from thence ; aud as it passed in places, 
where the roof over it was naturally much thinner, as well as 
greatly weakened by the undermining of these fires, it opened 
itself a passage, and burst forth. 
rest upon matter, in some degree, though not perfectly fluid, and that this 
matter is lighter than the earth that rests upon it. This conjecture, how- 
ever, will probably be thought less strange, if it be considered, that the new 
islands, formed about Santerini and the . ‘Azoxes; have some of them been 
raised from 200 to 300 yards, and upwards; a height which might well 
enough intitle them to the denomination of mountains, if they had been raised 
from lands not lying under the ocean. [See fig. 3.] * See art. 54. 
See also art. 94 to 97 inclusive. + See the note to art. 63. 
} Both the wave and previous retreat have been observed in the other 
great earthquakes, which have bappened at Lima, and in the neighbouring 
country. See d’Ulloa’s Voyage to Peru, part ii. book i. chap. 7. 
§ If these volcanos were not new ones, but only old ones which broke out 
afresh, [see the note to art. 34.] the argument will come with still greater 
' force. || See art. 28. 
80. As 
