Volcanos and Earthquakes. 27 



1814, 1815, 1819, and 1820, endeavoured to explain the 

 phenomena by the oxidation of the metals of the alkalies and 

 earths.* He thinks himself justified in supposing the caverns 

 beneath the Solfatara of Fitzzuoli to have a subterranean 

 communication with Vesuvius, because whenever the latter is 

 tn action, the former is in repose. A slip of paper which 

 Davy threw into the mouth of the Solfatara, during an erup- 

 tion of Vesuvius, was not rejected, from which he concluded 

 that there must be a descending current of air. The subterra- 

 nean thunder, which is heard at such great distances from be- 

 neath Vesuvius, seems to him to indicate the existence of great 

 subterranean caverns, filled with gaseous substances, and that 

 the same caverns which, during the activity of the volcano, con- 

 tinue for a long time to eject enormous quantities of aqueous 

 vapour, must be filled, during its repose, with atmospheric air. 

 In proof of the existence of extensive caverns, he mentions those 

 in the limestone of Carniola. Now, as the metals of the earths 

 in the supposed volcanic caverns are not only exposed to the ac- 

 tion of the air but also to that of aqueous vapour, they will 

 be oxidized at the expense of both, and be converted into lava. 

 He thinks his hypothesis capable of explaining all the phenc- 

 mena which he observed. 



Davy also touches upon the circumstance, often mentioned 

 by geologists, that almost all great volcanos are situated near 

 the sea.t Supposing their first ei'uption to have been caused 

 by the action of the sea-water upon the metals of the earths, 

 and the metallic oxides, ejected from the craters in the form of 

 lava, to have left vast caverns, the succeeding eruptions would 

 be effected by the oxidations which would ensue in those ca- 



* Sur les Phenom^nes des Volcans. Annalcs de Cliim. et de Pliys. 

 vol. xxxvii. p. 133. 



t Tlvat volcanos may act at a great distance from the sea is proved by the 

 Pesckan in the centre of Asia, whicli is 2G0 geographical miles distant from any 

 great sea, and from which streams of lava have issued within the period of 

 our history. Even the opinion that the vicinity of extensive lakes operates 

 on the volcanos of Central Asia, in the same manner as the ocean, isunfomid- 

 ed. The volcano of Tiirfan is surrounded by very mconsiderabie lakes, and 

 the lake of Temartu or Tssikul, wliich is not twice as large as the Lake of Gt' 

 nera, lies fully 25 geographicjd miles from Pesckan. See oleo Girardin in ojv 

 position to Davy's hypothesis in Jameson's Phil. Journ. vol. ix. py ia€. 



