1 08 Volcanos. 



points in these discussions, which will probably never be 

 settled, and about which there will continue to be a diversity 

 of opinion. 



Analysis of the 



CONSIDERATIONS ON VOLCANOS, BY G. POULETT 

 SCROPE, FSQ. 



Sec. Geol. Soc. 



" Describing generally what is meant by volcano, and by lava, 

 in which the author properly includes all volcanic rocky erupted 

 matter, under whatever form it may be disposed on the surface, 

 Mr. S. proceeds to state the known volcanos at 200; afterwards 

 showing reason to think this to be much less than the number 

 probably existing in the world. The arguments for this opinion 

 consist in our ignorance of the interior of great continents, in the 

 probability of unknown marine volcanos, and in the fact that, for 

 want of observers and records, many which have broken out at 

 distant times, are unknown or forgotten. 



" To the terrestial volcanos he has given the term subaerial, 

 and to the marine the appellation of subaqueous. 



" In the first class, the character of the appearances varies ac- 

 cording to the incidental fact of the volcano being new or appear- 

 ing through an ancient vent. But it is not very certain that we 

 know of any rigidly new ; as even the eruptions of Yorullo are 

 considered as coming from vents subsidiary to former ones. Au- 

 vergne, however, and the well-known country connected with it, 

 in this respect, as well as the volcanic territory of the Rhine, 

 preserve the records of volcanos which have been once of this 

 character, and where therefore the circumstances can be studied 

 with facility. 



" With respect to the other case, the author proceeds to in- 

 vestigate the phenomena of active volcanos, dividing them into 

 three classes, which he calls phase of permanent eruption, phase 

 of moderate activity, and phase of prolonged intermittences. 



" In the first class Stromboli is an unquestioned example ; and 

 the same appears true of the volcano in the Lake of Nicaragua. 

 The second class includes the great mass of volcanos known as 

 such ; and among those, Vesuvius and iEtna are the most familiar 

 and the best studied, from the free and frequent access which 

 they have permitted for so many years, to persons endowed 

 Avith the capacity for observation. This is also the character 

 of the volcanos of the Pacific, of those of Kamtschatka, and 

 the Molucca and Phillippine Islands, and indeed generally of 

 many more whose histories are to be found without end in works, 



