106 HISTORY OF 



given to the earth at one place, and that being 

 communicated onward by an undulatory motion, 

 successively affects different regions in its pro- 

 gress ; as the blow given by a stone falling in a 

 lake is not perceived at the shores till some time 

 after the first concussion. 



The shock is sometimes instantaneous, like the 

 explosion of gunpowder ; and sometimes tremu- 

 lous, and continuing for several minutes. The 

 nearer the place where the shock is first given, 

 the more instantaneous and simple it appears. At 

 a greater distance, the earth redoubles the first 

 blow, with a sort of vibratory continuation. 



As waters have generally so great a share in 

 producing earthquakes, it is not to be wondered 

 that they should generally follow those breaches 

 made by the force of fire, and appear in the great 

 chasms which the earthquake has opened. 



These are some of the most remarkable pheno- 

 mena of earthquakes, presenting a frightful assem- 

 blage of the most terrible effects of air, earth, fire, 

 and water. 



The valley of Solfatara, near Naples, seems to 

 exhibit, in a minuter degree, whatever is seen of 

 this horrible kind on the great theatre of nature. 

 This plain, which is about twelve hundred feet 

 long, and a thousand broad, is embosomed in 

 mountains, and has in the middle of it a lake of 

 noisome blackish water, covered with a bitumen 

 that floats upon its surface. In every part of this 

 plain, caverns appear smoking with sulphur, and 

 often emitting flames. The earth, wherever we 

 walk over it, trembles beneath the feet. Noises 



