TRUE VOLCANOES. 233 



Western Horn, and again in the Bay of the Gorilla Apes, 

 on the West African coast.* Such particular descriptions 

 may be believed to rest upon actual observation of nature ! 



The smallest and greatest elevation of the points at which 

 the volcanic energy of the interior of the earth shows itself 

 permanently active at the surface is a hypsometric consider- 

 ation possessing that interest for the physical description of 

 the earth which belongs to all facts relating to the reaction 

 of the fluid interior of the planet upon its surface. The de- 

 gree of the upheaving forcef is certainly evidenced in the 

 height of volcanic conical mountains, but an opinion as to 

 the influence of comparative elevation upon the frequency 

 and violence of eruptions must be given with great caution. 

 Individual contrasts of the frequency and strength of simi- 

 lar actions in very high or very low volcanoes can not be 

 decisive in this case, and our knowledge of the many hun- 

 dred active volcanoes supposed to exist upon continents and 

 islands is still so exceedingly imperfect, that the only deci- 

 sive method, that of average numbers, is as yet misapplied. 

 But such average numbers, even if they should furnish the 

 definite result at what elevation of the cones a quicker re- 

 turn of the eruptions is manifested, would still leave room 

 for the doubt that the incalculable contingencies occurring; in 

 the net-work of fissures, which may be stopped up with more 

 or less ease, may act together with the elevation; that is to 

 say, the distance from the volcanic focus. The phenomenon 

 is consequently an uncertain one as regards its causal con- 

 nection. 



Adhering cautiously to matters of fact, where the compli- 

 cation of the natural phenomena and the deficiency of his- 

 torical records as to the number of eruptions in the lapse of 

 ages have not yet allowed us to discover laws, I am content- 

 ed with establishing five groups for the comparative hypso- 

 metry of volcanoes, in which the classes of elevation are 

 characterized by a small but certain number of examples. 

 In these five groups I have only referred to conical mount- 

 ains rising isolated and furnished with still ignited craters, 

 and consequently to true and still active volcanoes, not to 

 unopened dome-shaped mountains, such as Chimborazo. All 

 cones of eruption which are dependent upon a neighboring 

 volcano, or which, when at a distance from the latter, as 



* Humboldt, Examen Critique de 1'IIist. de la Ge'ogr., t. iii., p. 135 ; 

 Hannonis Periplus, in Hudson's Geogr. Grceci min., t. i., p. 45. 

 t Cosmos, vol. i. p. 229. 



