88 A VOYAGE TO Book VIL 



compresses it by its greater expansion, and at the same 

 time rarefies it by its heat ; but the cavities being too 

 narrow to admit of its proper dilatation, it struggles 

 for a Yeut, and these eilbrts shake all the contiguous 

 parts ; till at last, Avhere it finds the least resistance, 

 it forces itself a passage, whigh sometimes closes 

 again by the tremulous motion it occasions, and at 

 others continues open ; as may be seen in different 

 parts of all these countries. When on account of 

 the resistance being equal, it finds a passage in seve- 

 ral parts, the chasms or fissures are generally smaller, 

 so that rarely any vestiges remain after the concus- 

 sion. At other times *•, hen the subterranean cavities 

 are so large as to form subtcrraneart caverns, they not 

 only rend the earth, and at eVery shock leave it fnll 

 of disruption , but also cause it to sink into spa- 

 cious hollows ; as I particularly observed near the 

 town of Guaranda, a place in the jurisdiction of 

 Chimbo, in the province of Quito ; where in the 

 year 1744 all the ground on the one side of the chasm 

 sunk near a yard, the other side rising in the same 

 proportion, though with some inequalities on both 

 sides. 



The loud subterraneous noises preceding earth- 

 quakes, and which imitate thunder at a distance, 

 seem to correspond with theabove-mentioned cause and 

 formation of earthquakes, as they can only proceed 

 from the rarefaction of the air on the ignition of the 

 explosive substances; which being impetuously pro- 

 pagated through all the caverns of the earth, propel- 

 ling and at the same time dilatin?.'; what is contained in 

 them, till all the cavities being pervaded, and no vent 

 found, the elforts for a further dilatation begin, and 

 form the concussion with which it terminates. 



It must be observed that at the time \Nhen the air, 

 ■which had been confined within the earth, bursts 

 through it, neither the light nor fire emitted from 

 the chasms aie seen. The reason is, that this light 



and 



