ULLOA*S VOYAGE TO SOUTH AMERICA. 595 



of the refiflance being equal, it finds a paffage in feveral parts, the chafms or fiffures 

 are generally fmaller, fo that rarely any veftiges remain after the concuffion. At other 

 times, when the fubrerranean cavities are fo large as to form fubterranean caverns, they 

 not only rend the earth, and at every ihock leave it full of difruptions, but a'lfo caufe it 

 to fink into fpacious hollows, as I particularly obferved near the town of Guaranda, a 

 place in the jurifdidlion of Chimbo, in the province of Quito ; where, in the year 1744, 

 all the ground on the one fide of the chafm funk near a yard, the other fide rifing in 

 the fame proportion, though with fome inequalities on both fides. 



The loud fubterranean noifes preceding earthquakes, and which imitate thunder at 

 a diftance, feem to correfpond with the above-mentioned caufe and formation of earth- 

 quakes, as they can only proceed from the rarefadion of the air on the ignition of the 

 explofive fubflances ; which being impetuoufly propagated through all the caverns of 

 the earth, propelling and at the fame time dilating what is contained in them, till all the 

 cavities being pervaded, and no vent found, the efforts for a further dilatation begin, 

 and form the concuffion with which it terminates. 



It miifi: be obferved that at the time when the air, which had been confined within 

 the earth, burfls through it, neither the light nor fire emitted from the chafms are feen. 

 The reafon is, that this light and fire exift only at the inftant when the matter becomes 

 injBamed, and the air fpreading itfelf through all the veins, the light is extinguished by 

 its dilatation, and becomes afterwards imperceptible. It is neceffary to fuppofe that 

 there muft be fome, though a fhort interval, between the inflammation and effeft. 

 Neither is the flame permanent, the fubftance ignited not containing thofe folid and 

 oleaginous particulars which fupply the volcanoes. Btfides, they are not in fufEcient 

 quantity to afcend from the fubterraneous caverns where they took fire, to the fuperfi- 

 cies of the earth. Farther, this not being the place where the matter was originally 

 contained, but that where it has forced a palfage for the quantity of air which its rare- 

 fadion augmented, the firft light is loft among the meanders of its courfe, and there- 

 fore not to be feen when the wind violently forces a paiTage. 1 here have, however, 

 been inftances when the light has been feen, though much oftener the fmoke ; but this 

 is generally loft in the clouds of duft afcending at the time of the concuflion. 



The ftiocks are repeated at intervals, of a few days, fometimes of a few hours ; pro- 

 ceeding from the matter being difperfed in different places, and each in a different de- 

 gree of aptitude for inflammation, one part kindling after another fucceflively, as each 

 is more or lefs prepared. Hence proceed alfo the different violence of the Ihocks and 

 the different intervals of time. For the quantity firft inflamed increafes by its heat other 

 inflammable portions of matter ; whence a part which would not have been ignited till 

 after fome days, by means of this adventitious fire, becomes fo within a few hours. The 

 fecond fhocks are more violent, and caufe a greater deftruftion than the firft ; for the 

 fire of the portion of matter which is firft inflamed, though in itfelf fmall, is fufEcient to 

 accelerate the fermentation of a much larger quantity, and confequently m.uft be attended 

 with more powerful effeds. 



Though the fummer here, as we have already obferved, is confiderably warm, yet it 

 is not produ6:ive of venomous creatures, which in this country are not known ; and thf 

 fame may be faid of all Valles, though there are fome parts, as Tun.bez and Piura, 

 where the heat is nearly equal to that at Guayaquil. This fingularity can therefore pro- 

 ceed from no other caufe than the natural drought of the climate. 



The diftempers moft common at Lima are malignant, intermittent, and catarrhous 

 fevers, pleurifies, and conftipations ; and thefe rage continually in the city. • The fraall- 



4 G a pox 



