164 TRAVELS THROUGH 



Guettard has affured me, that in France they are 

 commonly to be met with in flate. But nothing 

 more eafy than an explanatory hypothefis of thefe 

 phenomena. 



After thefe my obfervations on Vefuvius, I will 

 defcribe Svlfatara. 



This place feems undoubtedly to have been a 

 volcano, which, after having been burnt out, funk 

 into itfelf, and left a crater-like ground incloled 

 with fome remains of its fides. Its inner ground 

 is covered by a flat roof of a white ciayifh earth, 

 whofe hollow found indicates deeper caverns. 

 There appear no flames, either in its fifiures, or 

 in the artificial holes, which for the gathering of 

 the falmiac are dug into it ; but a ftrong fulphu- 

 reous aluminous fmoke or fleam, fmelling like 

 hepar fulphuris, iflues out from thefe fiffures of 

 the floor, and from its white elevated inclofures, 

 which furround it in an amphitheatrical form. 



Rain and other waters penetrate by the cracks 

 of its floor into its fubterraneous caverns; become 

 there boiling by heat ; diflblve the faline and ful- 

 phureous materials; evaporate in fleams, or run 

 with a fenfible noife by fubterraneous canals and 

 caverns to the other fide of Solfatara, where in 

 the Pifdarelle they appear rifing from under 

 ground. Thefe Pifdarelle are two or three fmall 

 fpoutings of hot aluminous and fulphureous water, 



on 



