TRUE VOLCANOES. 245 



in the network 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 pheno- 

 menon is consequently an uncertain one, as regards its 

 causal connexion. 



Adhering cautiously to matters of fact, where the compli- 

 cation of the natural phenomena and the deficiency of histo- 

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

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

 tented with establishing five groups for the comparative 

 hypsometry of volcanoes, in which the classes of elevation are 

 characterised by a small but certain number of examples. 

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

 tains 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 neighbouring 

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

 upon the island of Lancerote, and in the Arso on the 

 Epomeus of Ischia, have preserved no permanent connection 

 between the interior of the earth and the atmosphere, are 

 here excluded. According to the testimony of the most 

 zealous observer of the vulcanicity of Etna, Sartorius von 

 Waltershausen, this volcano is surrounded by nearly 700 

 larger and smaller cones of eruption. As the measured ele- 

 vations of the summits relate to the level of the sea, the 

 present fluid surface of the planet, it is of importance here 

 to advert to the fact that insular volcanoes, of which some 

 (such as the Javanese volcano Cosima, 16 at the entrance of 

 the Straits of Tsugar, described by Horner and Tilesius) do 

 not project a thousand feet, and others, such as the Peak of 

 Tenerifie, 17 are more than 12,250 feet above the surface of 



16 For the position of this volcano, which is only exceeded in small- 

 noss by the volcano of Tanna, and that of the Mendaiia, see the fine 

 map of Japan by F. von Siebold, 1840. 



17 I do not mention here, with the Peak of Teneriffe, amongst the 

 insular volcanoes, that of Mauna-Roa, the conical form of which does 

 not agree with its name. In the language of the Sandwich Islanders, 

 mauna signifies mountain, and roa, both long and much. Nor do I 

 mention Hawaii, upon the height of which there has so long been a 

 dispute, and which has been described as a trachytic dome not opened 

 at the summit. The celebrated crater Kiraueah (a lake of molten, 



