Cheviical Theory of Volcanos. 293 



Now, in proof of this general proximity, it may be re- 

 marked, that out of a catalogue of no less than 163 active 

 vents enumerated by M. Arago, as occurring in various parts 

 of the known world, all, excepting two or three in different 

 parts of America, and about the same number of which we 

 possess very imperfect information, in Central Asia, are within 

 a short distance at least of the ocean. It is even found that 

 the very excepted cases, when examined, tend to confirm the 

 rule, being so situated, that their connection, either with the 

 ocean or with inland seas that may supply its place, becomes 

 a matter of fair inference. In proof of this, we need only re- 

 fer to the descriptions given by Humboldt of JoruUo ; from 

 which it appears, that distant as this mountain may be both 

 from the Atlantic and Pacific Oceans, it is nevertheless con- 

 nected with one or both through the medium of a chain of 

 volcanic eminences ; and even the volcanos of Tartary, whose 

 existence in an active condition is more problematical, may be 

 connected with some of these extensive salt lakes which seem 

 to abound in the depressed portion of Central Asia. 



2d Objection. — Atmospheric air cannot gain admittance to the 

 focus of a volcano, because there must be an enormous force 

 acting outwards to protrude the liquid lava to so great a height, 

 and as this pressure continues for many years, during which 

 time the phenomena by no means abate in activity, it is im- 

 possible that air should in any way contribute to it. 



Answer. — The very conditions of our theory imply the exist- 

 ence near and about the focus of the volcano of vast caverns, 

 caused, originally by the heaving up of the softened rocks, 

 owing to the elastic vapours disengaged, and consequently 

 filled in the first instance by these matters. But the amount of 

 these vapours must be undergoing continual oscillation. \sty 

 Owing to differences of temperature caused by the constantly 

 varying intensity of the volcanic action. 9.dly, By the reaction 

 of the gases upon each other, as for instance, sulphuretted hy- 

 drogen upon sulphurous acid, muriatic and carbonic acids upon 

 ammonia, the fixed alkalies and the earths. 3(%, By the ever- 

 varying proportion between the amount of water decomposed 

 by the alkaline or earthy metals, and generated by the union of 

 hydrogen to the oxygen present. Hence, unless the passages 



