260 



ingeniously observes, the greater or less depth of 

 the crater is an infallible indication of the prox- 

 imity of a new eruption. 



I might terminate these geological sketches 

 by discussing the nature of the combustible, 

 which feeds, for so many thousands of years, 

 the fire of the Peak of TenerifFe ; I might examine 

 whether it be sodium or potassium, the metallic 

 basis of some earth, carburet of hydrogen, or 

 pure sulphur combined with iron, that burns in 

 the volcano ; but wishing to limit myself to what 

 maybe the object of direct observation, I will 

 not take upon me to solve a problem, for which 

 we have not yet sufficient data. We are igno^ 

 rant, whether we should conclude from the 

 enormous quantity of sulphur contained in the 

 crater of the Peak, that it is this substance 

 which keeps up the heat of the volcano ; or 

 whether the fire, fed by a combustible of an 

 unknown nature, effects merely the sublimation 

 of the sulphur. What we learn from observa- 

 tion is, that in craters which are still burning 

 sulphur is very rare ; while all the ancient vol- 

 canoes finish by remaining true sulphur pits. 

 We might presume, that in the former the sul- 

 phur is combined with oxygen, while in the lat- 

 ter it is merely sublimed; for nothing hitherto 

 authorises us to admit, that it is formed in the 

 interior of volcanoes, like ammonia and the 

 neutral salts. When we were yet unacquainted 



