262 Volcanoes, 



Art. IX. Volcanoes, By W. M. Higgins, Esq. F.G.S., and 

 J. W. Draper, Esq. 



(Continued from p. 172.) 



The Phenomena which attend Eruption, — Volcanic erup- 

 tions are not periodical, as some persons have supposed; the 

 period and intensity of their action are decidedly irregular. 

 This is proved by the history of almost every volcano with 

 which we are acquainted. Some general classification, how- 

 ever, may be formed, dependent on a certain similarity in the 

 method and periods of eruption in different volcanoes : some 

 are in a state of incessant moderate action ; in some we find 

 short intervals of repose alternating with lengthened periods 

 of eruption ; while others are characterised by lengthened 

 quiescence and paroxysms of excessive violence. Here, then, 

 we have three classes of volcanic action, which have been 

 thus arranged by geologists : — 1 . Phase of permanent erup- ' 

 tion ; 2. Phase of moderate activity ; 3. Phase of prolonged 

 intermittences. 



Volcanoes of permanent Eruption are very few in number: 

 we are not perfectly acquainted with more than three, that of 

 Stromboli, one of the Lipari Isles ; the Devil's Mouth, in the 

 Lake of Nicaragua ; and one in the Isle of Bourbon. 



Stromboli has been in a state of constant activity for more 

 than two thousand years, and is a good type of this class : 

 lava seldom overflows its crater, but large masses of burning 

 rocks and scoriae are incessantly ejected in a perpendicular 

 direction. This phenomenon, accompanied by a loud explo- 

 sion, occurs every seven or eight minutes ; of which fact we 

 are informed by Pliny, as well as by modern travellers. 



Dolomieu examined this interesting mountain, and has 

 given us the following description of its eruptions : — " The 

 inflamed crater is on the north-western part of the isle, on the 

 side of the mountain. I saw it dart, during the night, at 

 regular intervals of seven or eight minutes, ignited stones^ 

 which rose to the height of more than a hundred feet, form- 

 ing rays a little divergent, but of which the greater quantity 

 fell back into the crater, while others rolled even to the sea.'* 



On the following day he ascended an eminence of the 

 mountain, from which he obtained a still more interesting view 

 of the volcano. " The crater," he says, " is very small ; I 

 do not think it exceeds fifty paces in diameter, having the 

 form of a funnel terminating in a point. During all the time 

 I observed it, the eruptions succeeded with the same regu- 

 larity as during the preceding night. The approach of the 



