234 COSMOS. 



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

 meus of Ischia, have preserved no permanent connection be- 

 tween the interior of the earth and the atmosphere, are here 

 excluded. According to the testimony of the most zealous 

 observer of the vulcanicitj of ^tna, Sartorius von Walters- 

 hausen, this volcano is surrounded by nearly 700 larger and 

 smaller cones of eruption. As the measured elevations 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,* 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 Teneriffe,t are 

 more thian 12,250 feet above the surface of the sea — have 

 raised themselves by volcanic forces above a sea-bottom, 

 which has often been found 20,000 feet, nay in one case 

 more than 45,838 feet, below the present surface of the ocean. 

 To avoid an error in the numerical proportions it must also 

 be mentioned that, although distinctions of the first and fourth 

 classes— volcanoes of 1000 and 18,000 feet (1066 and 19,188 

 English feet) — appear very considerable for volcanoes on con- 

 tinents, the ratios of these numbers are quite changed if 

 (from IVIitscherlich's experiments upon the melting point of 

 granite, and the not very probable hypothesis of the uniform 

 increase of heat in proportion to the depth in arithmetical 

 progression) we infer the upper limit of the fused interior of 

 the earth to be about 121,500 feet below the present sea- 

 level. Consiflering the tension of elastic vapors, which is 

 vastly increased by the stopping of volcanic fissures, the dif- 

 ferences of elevation of the volcanoes hitherto measured are 

 certainly not considerable enough to be regarded as a hinder- 

 ance to the elevation of the lava and other dense masses to 

 the height of the crater. 



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

 ness by the volcano of Tanna, and that of 'the Mendana, see the fine 

 map of Japan by F. von Siebold, 1840. 



t I do not mention here, with the Peak of TenerifFe, among the in- 

 sular 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 7nuch, Nor do I men- 

 tion Hawaii, upon the height of which there has so long been a dis- 

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

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

 ing lava) lies to the eastward, near the foot of the Mauna-Roa, accord- 

 ing to Wilkes, at an elevation of 3970 feet. See the excellent de- 

 scription in Charles Wilkes's Exploring Expedition, vol. iv., p 165-196. 



