THE SUBTERRANEAN I-TKNACE 343 



munication with the exterior. By offering perma- 

 nent vents to the subterranean vapors that tend 

 to liberate themselves by overturning the earth, they 

 rend.-r earthquakes less frequent and less disastrous. 

 In vole-anil' countries every time the ground is 

 shaken by strong shocks, the earthquake ceases the 

 moment the volcano begins to throw up its fumes 

 and lava/' 



"I well remember/' said Jules, "your account of 

 the eruption of Etna and the Catanian disaster. At 

 first I only saw in volcanoes terrible mountains 

 -{reading devastation around them; now I begin to 

 their great use, their necessity. Without their 

 air-holes, the earth would seldom be still. " 



