ON ITS EXTERIOR. VOLCANOES. 243 



recur oftenest, there would still remain room for doubt 

 how far the influence of height, or distance from the 

 volcanic hearth, was modified by all the incalculable 

 accidental circumstances, which may render the network 

 of fissures more or less impeded, or more or less easily 

 traversed. The phenomenon is then, in respect to causal 

 connection, " indeterminate." 



Keeping cautiously to the facts only, where the com- 

 plexity of the phenomena, and the want of historical 

 information respecting the number of eruptions in the 

 course of centuries, do not yet permit us to arrive at 

 laws, I will content myself, in regard to the comparative 

 hypsometry of volcanoes, with giving a table of five 

 groups, in which the different classes of elevation are 

 represented by a small number of well-authenticated 

 examples. I have included in these five groups only 

 detached mountains having craters still burning, there- 

 fore, active volcanoes strictly so called, not unopened 

 domes, as Chimborazo. All cones of eruption are ex- 

 cluded which are dependent on an adjacent volcano, or 

 which, at a distance therefrom, as in the Island of 

 Lancerote, and in the Arso at the Epomeo in Ischia, 

 have not preserved any permanent communication be- 

 tween the interior and the atmosphere. According to 

 the testimony of that most zealous investigator of all 

 that belongs to Mount Etna, Sartorius von Walter shausen, 

 that volcano is surrounded by nearly 700 greater and 

 lesser cones of eruption. As the measured heights of 

 all summits are taken in relation to the level of the 

 sea (the present liquid surface of our planet), it is 

 important here to remind the reader, that island 

 volcanoes of which some, as the Japanese volcano 



