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THE POPULAR SCIENCE MONTHLY. 



of earthquake-shocks in the country around, the vivid lightnings and 

 thunders arising from the electrical action engendered by the column 

 of steam, and the excessive rainfall which followed the condensation 

 of the steam. 



In both these volcanoes the active cause of all the phenomena ex- 

 hibited is found to be the escape of steam from the midst of masses 



of incandescent liquefied rock. The violence, the grandeur, and the 

 destructive effects of an eruption depend upon the abundance and 

 tension of this escaping steam. 



The manner in which volcanic cones are built up is ascertained 



