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within an extent of 120 miles long, and lefs than 
thirty broad, the loweft of which exceeds the height 
of Riobamba by above two thirds of a mile, and the 
higheft by more than twice that quantity. Now, as 
the earthquakes have been more violent at the foot of 
thefe mountains, than in the lower lands, fo they 
have been hill more violent towards the tops of them : 
this is iufficiently manifeft, from the many * rents 
made in them, and the rocks that have been broken 
oft from them, upon fuch occafions : but it appears 
hill more manifehly, and beyond all difpute, in the 
bui fling forth of volcanos, which are almoft always 
at the very -f fummit of the mountains, where they 
are found. In thefe inftances, the earth, hones, &c, 
which lay over the fire, are generally fcattered by the 
violence of the vapour, that breaks its way through, 
to the dihance of iome miles round about. 
8 y . The great earthquake of the 1 h November 
I 7ff> was a lf° more violent amongh the mountains, 
than at the city of Lifbon. We are told, that “ the 
“ mountains of Arrabida, Ehrella, Julio, Marvan, 
and Cintra, being fome of the largeh in Portugal, 
tc were impetuoufly fhaken, as it were, from their 
“ very foundations; and moh of them opened at 
“ their fummits, fplit and rent in a wonderful man- 
“ ner, and huge maffes of them were thrown down 
<{ into the fubjacent vallies J.” 
See d’Ulloa’s Voyage to Peru, part i. book vi. chap. 2 . 
t 1 he only exceptions that I know of to this rule, are in thofq. 
cafes, where the higheft part having an opening already, fome 
frem mouth opens itfelf in t' e fide of the mountain. 
X See Hift. andPhilof. of Earthq. p. 317. 
86. The 
