i68 EFFECTS of HEAT 



as pipes through which the lavas of the lateral eruptions were 

 conveyed to the open air. This fcene prefents to the view 

 of an attentive obferver, a real fpecimen of thofe internal ftreams 

 which we have juft been confidering in fpeculation, and they 

 may exhibit circumflances decifrve of the opinions here ad- 

 vanced. For, if one of thefe ftreams had formerly been con- 

 nected with a lateral eruption, dilcharged at more than 600 

 feet above the At Ho del Cavallo, it might poffibly contain the 

 carbonate of lime. But could we fuppofe that depth to extend 

 to 1708 feet, the interference of air-bubbles, and the action 

 of a ftronger heat than was merely required for the fufion of 

 the carbonate, might have been overcome. 



Perhaps the height of Vefuvius has never been great enough 

 for this purpofe. But could we fuppofe iEtna to be cleft in 

 two, and its ftru&ure displayed, as that of Vefuvius has juft 

 been defcribed, there can be no doubt that internal ftreams of 

 lava would be laid open, in which the preflure muft have far 

 exceeded the force required to conftrain the carbonic acid of 

 limeftone ; fince that mountain occafionally delivers lavas from 

 its fummit, placed 10.954 feet above the level of the Mediterra- 

 nean *, which wafhes its bafe. I recollect having feen, in fome 

 parts of ^tna, vaft chafms and crags, formed by volcanic re- 

 volutions, in which vertical ftreams of lava, fimilar to thofe of 

 Somma, were apparent. But my attention not having been 

 turned to that objecl: till many years afterwards, I have only 

 now to recommend the inveftigation of this interefting point 

 to future travellers. 



Wh at has been faid of the heat conveyed by internal volca- 

 nic ftreams, applies equally to that deeper and more general 

 heat by which the lavas themfelves are melted and propelled 



upwards. 



* Phil. "Tratif. 1777, p. 595. 



