224 COSMOS. 



mixtures of augite and labradorite ; and hence arise the 

 different nature and external conformation of these enclosures 

 of craters. No phenomena of eruptions are manifested in such 

 craters, as they open no permanent channel of communication 

 with the interior, and it is but seldom that we meet with 

 traces of volcanic activity either in the neighbourhood or in the 

 interior of these craters. The force which was able to produce 

 so important an action must have been long accumulating in 

 the interior before it could overpower the resistance of the 

 mass pressing upon it : it sometimes, for instance, on the 

 origin of new islands, will raise granular rocks and conglome- 

 rated masses (strata of tufa filled with marine plants), above 

 the surface of the sea. The compressed vapours escape through 

 the crater of elevation, but a large mass soon falls back and 

 closes the opening which had been only formed by these 

 manifestations of force. No volcano can, therefore, be pro- 

 duced.* A volcano, properly so called, exists only where a 

 permanent connexion is established between the interior of 

 the Earth and the atmosphere, and the reaction of the interior 

 on the surface then continues during long periods of time. 

 It may be interrupted for centuries, as in the case oi 

 Vesuvius, Fisove,f and then manifest itself with renewed ac- 



* Leopold von Buch, Phys. Beschreibung der CanariscJien Iweln, 

 6.326; and his Memoir uber Erhebungscratere und Vulc.ane, inPoggend. 

 Annal, bd. xxxvii. s. 169. 



In his remarks on the separation of Sicily from Calabria, Strabo gives 

 an excellent description of the two modes in which islands are formed : 

 " Some islands," he observes (lib. vi. p. 258, ed. Casaub.) " are frag- 

 ments of the continent, others have arisen from the sea, as even at the 

 present time is known to happen : for the islands of the great ocean, 

 lying far from the main land, have probably been raised from its depths, 

 while on the other hand those near promontories appear (according to 

 reason) to have been separated from the continent." 



f Ocre Figove (Mons Vesuvius), in the Umbrian language (Lassen, 

 Deutung der Eugubinischen Tafeln in Rhein. Museum, 1832, s. 387.) 

 The word ochre is very probably genuine Umbrian, and means, according 

 to Festus, mountain. ^Etna would be a burning and shining mountain, 

 if Voss is correct hi stating that A'irvrj is an hellenic sound, and is 

 connected with aWw and aWivog; but the intelligent writer, Parthey, 

 doubts this hellenic origin on etymological grounds, and also because 

 Mtna, was by no means regarded as a luminous beacon for ships or 

 wanderers, in the same manner as the ever-travailing Stromloli, (Stron- 

 gyle), to which Homer seems to refer in the Odyssey (xii., 68, 202, 



