THE EARTH 47 



ticular answers might be easily given ; as, that the length of the funnel 

 increases the force of the explosion ; that the sides of the funnel are 

 actually often burst with the great violence of the flame ; that air 

 may be supposed at depths at least as far as the perpendicular fissures 

 descend. But the best answer is a well-known fact ; namely, that the 

 quantity of matter discharged from jEtna alone, is supposed, upon a 

 moderate computation, to exceed twenty times the original bulk of the 

 mountain.* The greatest part of Sicily seems covered with its erup- 

 tions. The inhabitants of Catanea have found, at the distance of seve- 

 ral miles, streets and houses sixty feet deep, overwhelmed by the lava 

 or matter it has discharged. But what is slill more remarkable, the 

 walls of these very houses have been built of materials evidently 

 thrown up by the mountain. The inference from all this is very ob- 

 vious ; that the matter thus exploded cannot belong to the mountain 

 itself, otherwise it would have been quickly consumed ; it cannot be 

 derived from moderate depths, since its amazing quantity evinces, that 

 all the places near the bottom must have long since been exhausted ; 

 nor can it have an extensive, and, if I may so call it, a superficial 

 spread, for then the country round would be quickly undermined ; it 

 must, therefore, be supplied from the deeper regions of the earth ; 

 those undiscovered tracts where the Deity performs his wonders in 

 solitude, satisfied with self-approbation ! 



CHAPTER X, 



OF EARTHQUAKES. 



HAVING given the theory of volcanoes, we have, in some measure, 

 given also that of earthquakes. They both seem to proceed from the 

 same cause, only with this difference, that the fury of the volcano is 

 spent in the eruption ; that of an earthquake spreads wider, and acts 

 more fatally by being confined. The volcano only affrights a province, 

 earthquakes have laid whole kingdoms in ruin. 



Philosophers! have taken some pains to distinguish between the va- 

 rious kinds of earthquakes, such as the tremulous, the pulsative, the 

 perpendicular, and the inclined ; but these are rather the distinctions 

 of art than of nature, mere accidental differences arising from the 

 situation of the country or of the cause. If, for instance, the confined 

 fire acts directly under a province or a town, it will heave the earth 

 perpendicularly upward, and produce a perpendicular earthquake. 

 If it acts at a distance, it will raise that tract obliquely, and thus the 

 inhabitants will perceive an inclined one. 



Nor does it seem to me that there is much greater reason for Mr. 

 ^uffon's distinction of earthquakes. One kind of which he supposes^ 

 to be produced by fire in the manner of volcanoes, and confined to 

 but a very narrow circumference. The other kind he ascribes to the 

 struggles of confined air, expanded by heat in the bowels of the earth, 

 and endeavouring to get free. For how do these two causes differ ? 



Kircher, Mund. Subt. vol. i. p. 202. \ Aristotle, Agricola, Buffon. { Buffon, vol. ii. p. 32S 



