362 ON VOLCANOES AND EARTHQUAKES. 



Therasia, Automali, and Thia, according to Pliny, 

 were thus generated near Santorini ; and, more re- 

 cently, some smaller ones have been formed in the 

 same place, as before mentioned. In these, as in 

 other cases, flames and smoke have appeared in the 

 sea, marine earthquakes have been felt, and the water 



has been heated to boiling. 







Of the Produce of Volcanoes. 



The productions of Volcanoes are numerous and 

 various ; consisting of different gaseous matters, of 

 inflammable substances, and of various salts, minerals? 

 and rocks. A very brief notice of the greater number 

 of these must suffice ; as we are little able to throw 

 light on their origin, and as the minerals, which are 

 among the most interesting, belong to the department 

 of the mineralogist. 



The formation of flame is attributed, and appa- 

 rently with reason, to hydrogen gas produced from the 

 decomposition of water ; and its evaporation appears 

 to be the chief cause of the white smoke, resembling 

 cotton, or the produce of the high-pressure Steam 

 Engine, which is sometimes thrown up. It has also 

 been ascertained that Vesuvius throws out carbonic 

 acid, azote, muriatic acid, and sulphurous acid. Sul- 

 phur is said to be sometimes ejected by eruption ; but 

 it is, in general, sublimed by a slower process, during 

 periods of comparative repose. Boracic acid is one of 

 the rarer productions; occurring in Vulcano : and the 

 formation of siliceous stalactites, apparently deposited 

 from the steam of water, in Vesuvian eruptions, must 

 also be considered rare. Tourfan, in Tartary, pro- 

 duces muriat of ammonia. 



It was already remarked, that the black smoke of 

 volcanoes consisted of dust, or of the minutest frag- 



