88 M. Ga5'-Lussac on Vokanos. 



The necessity which appears to me to exist for the agency 

 of water in volcanic furrfaces, the presence of some hnncheil 

 parts of soda in hiva, as also ol sea-salt and of several other 

 chlorides, renders it very probable that it is sea-water which 

 most connnonly jienetrates into them. One objection, how- 

 ever, which I ought not to conceal, presents itself: namel}', 

 that it appears necessarily to follow from this supposition, that 

 the streams of lava would escape through the same channels 

 whicli had served to convey the water, since they would expe- 

 rience a slighter resistance in them than in those through which 

 they are raised to the surface of the earth. It might also be 

 expected that the elastic fluids formed in volcanic furnaces be- 

 fore the ascent of lava to the surface of tlie earth, would fre- 

 quentlv boil up through those same channels to the surface of 

 the sea. I am not aware that such a })hsenomenon has ever been 

 observed, though it is very probable that the mophefcs, so 

 common in volcanic countries, are produced by these elastic 

 fluids. 



On the other hand, we may remark that the long intervals 

 between the eruptions and the state of I'epose in which volcanos 

 remain for a great number of years, seem to demonstrate that 

 their fires become extinguished, or at least considerably dead- 

 ened ; the water would then penetrate gradually by its own pres- 

 sure into imperceptible fissures to a great depth in the interior 

 of the earth, and would accumulate in the vast cavities it con- 

 tains. The volcanic fires would afterv/ards gradually revive, 

 and the lava, after having obstructed the channels through 

 which the water penetrated, would rise to its accustomed vent ; 

 the diameter of which must continually increase by the fusion 

 of its coats. These are mere conjectures; but the fact is cer- 

 tain, that water does really exist in volcanic furnaces. 



It is evident that the science of volcanos is as yet involved in 

 much uncertainty. Although there are strong grounds for 

 tlie belief that the earth contains substances in a high degree 

 combustible, we are still in want of those precise observa- 

 tions which might enable us to appreciate theii agency in 

 volcanic phaenomena. For this purpose an accurate know- 

 ledge of the nature of the vapours exhaled by different vol- 

 canos is requisite ; for the cause Avhich keeps them in activity 

 being certainly the same in each, the products common to all 

 might lead to its discovery. All other products will be ac- 

 cidental ; that is to say, they will be the result of the action 

 of heat upon the inert bodies in the neighbourhood of the 

 volcanic furnace. 



The great number of burning volcanos spread over the sur- 

 face of the earth, and the still greater number of mineral masses 

 which bear evident marks of their ancient volcanic origin, ought 



to 



