till 



M Etna and the Eolian islands have been burning, and how 

 could this have continued so long, if the fire had not been fed 

 by the neighbouring sea ?" In order to explain the necessity 

 of the vicinity of the sea, recourse has been had, even in 

 modern times, to the hypothesis of the penetration of sea- 

 water into the foci of volcanic agency, that is to say, into 

 ieep-seated terrestrial strata. When I collect together all 

 the facts that may be derived from my own observation and 

 the laborious researches of others, it appears to me that 

 everything in this involved investigation depends upon the 

 questions whether the great quantity of aqueous vapours, 

 which are unquestionably exhaled from volcanoes even when 

 in a state of rest, be derived from sea-water impregnated 

 with salt, or rather, perhaps, with fresh meteoric water ; 01 

 whether the expansive force of the vapours (which at a depth 

 of nearly 94,000 feet is equal to 2800 atmospheres,) would le 

 able at different depths to counterbalance the hydrostatic 

 pressure of the sea, and thus afford them under certain 

 conditions a free access to the focus ;f or whether the forrna- 



vel mari vicina sunt, vel a mari protinus alluuntur : mare erodit ilia 

 facillime pergitque in viscera terrae. Itaque cum in aliena regna sibi 

 viain faciat, ventis etiam facit ; ex quo fit, ut loca quaeque maritima 

 maxime terrae motibus subjecta sint, parum mediterranea. Habea 

 quum in sulfuris venas venti furentes inciderint, unde incendia oriantui 

 JStnse tuae. Vides, quae mare in radicibus habeat, quae sulfurea sit, 

 quae cavernosa, quae a mari aliquando perforata ventos admiserit 

 aestuantes, per quos idonea flammae materies incenderetur." 



* [Although extinct volcanoes seem by no means confined k> the 

 neighbourhood of the present seas, being often scattered over the most 

 inland portions of our existing continents, yet it will appear that at the 

 time at -which they were in an active state, the greater part were in the 

 neighbourhood either of the sea, or of the extensive salt or freshwater lakes, 

 which existed at that period over much of what is now dry land. This 

 may be seen either by referring to Dr. Boue"'s map of Europe, or to that 

 published by Mr. Lyell, in the recent edition of his Principles of Geology 

 (1847,) from both of which it will become apparent, that at a compara- 

 tively recent epoch, those parts of France, of Germany, of Hungary, and 

 of Italy, which afford evidences of volcanic action now extinct, were 

 covered by the ocean. Daubeney, On Volcanoes, p. 605.] Tr. 



t Compare Gay Lussac, Sur les Volcans, in the Annales de Chimie, 

 t. xxii. p. 427, and Bischof, Warmelehre, s. 272. The eruptions of 

 imoke and steam which have at different periods been seen in Lance- 

 rote, Iceland, and the Kurile Islands, during the eruption of the neigh- 

 louring volcanoes, afford indications of the reaction of volcanic foe! 



