THE INTERIOR OF THE EARTH. 455 



Pacific Ocean is a vast circle of ijnrivomous mountains the west- 

 ern coasts of America, the Aleutian Islands, Kamtchatka, the Kuriles, 

 Japan, the Philippines, Molucca, down to the Sunda Islands and New 

 Zealand, being comprised therein. Aside from this immense belt only 

 isolated groups are found, but they are always disposed around the 

 borders of the sea, or near some lai'ge body of water. Does not this 

 geographical distribution force us to the conclusion that there exists 

 an intimate connection between volcanic phenomena and water ? Shall 

 not we say that infiltration of water is a necessary condition of erup- 

 tions, and that the force which expels the torrents of lava is due to the 

 pressure of steam ? 



This view finds a confirmation in the recent discoveries of the 

 chemical constitution of the gases emitted by volcanoes. According 

 to M. Charles Sainte-Claire Deville, the clouds that emanate from vol- 

 canoes consist pi'incipally of the vapor of water. M. Fouque estimated 

 at over 2,000,000 cubic metres the quantity of water thrown out from 

 Etna in a gaseous form during the eruption of 1865. The clouds of 

 vapors issuing from a crater in eruption often condense and fall in 

 delude-like rains, which make torrents of mud of the volcanic ashes. 

 The streams of lava are, moreover, so charged with vapors that they 

 acquire a remarkable fluidity. These vapors are rapidly disengaged 

 as the streams descend, and sometimes in suddenly escaping they occa- 

 sion miniature eruptions in the middle of a torrent of solidifying lava. 

 Marine salt and other elements of sea-water are found in the gaseous 

 products of eruptions and in the deposits of fumaroles as well ; and M. 

 Fouque's researches on the chemical composition of the emanations 

 from Vesuvius, Etna, and the volcano of Santorin, show that they are 

 in part the result of the decomposition of sea-water. 



Such accumulated proofs no longer allow us to doubt the constant 

 agency of water in the production of volcanic phenomena. It would 

 seem that sea-water passes into the subterranean reservoirs either by 

 percolation through fissures or by transudation under, the enormous 

 pressure it sustains. Coming in contact with the incandescent lava at 

 a great depth, it is vaporized, and the accumulation of steam causes 

 from time to time an explosion of these subterranean boilers. Although 

 the heat of the lava-streams is rapidly dissipated by contact with the 

 air, the temperature of the incandescent mass at the bottom of the 

 crater may be estimated at 2,000, for refractory metals are known to 

 melt in contact with the molten lava. Were it not over 1,200, the 

 pressure of the steam generated by matter thus heated would be ample 

 to account for the explosive force of eruptions. It is not necessary, 

 indeed, to assume so great a depth as twenty kilometres for the seat 

 of this force, in order to explain the existence of matter in fusion, for 

 there is nothing to militate against the supposition that the earth's 

 crust is thinner in volcanic regions than elsewhere. It is quite prob- 

 able that the inner surface of this crust is furrowed and fissured, espe- 



