326 EEACTION OF THE INTERIOR OF THE EARTH 



vapours resting upon it. ( 465 ) Such hollows were al- 

 ready made to play a part in the theory of decreasing 

 central heat by the immortal author of the " Protogaea," 

 " Postremo credibile est contrahentem se refrigeratione 

 crustam bullas reliquisse, ingentes pro rei magnitudine, 

 id est, sub vastis fornicibus cavitates" ( 466 ) The more 

 improbable it is that the thickness of the already soli- 

 dified crust of the earth should be the same in all regions, 

 the more important is the consideration of the number 

 and geographical position of the volcanoes which are or 

 have been open within historic times. Such a view of 

 the geography of volcanoes can only be perfected by 

 often renewed attempts. 



1. Europe. 



Etna, 



Volcano in the Li- 



paris, 

 Stromboli, 



Ischia, 

 Vesuvius, 

 Santorin, 

 Lemnos, 



All belong to the great basin of the Mediterranean 

 Sea, but to its European, not its African shores : all these 

 seven volcanoes are or have been active within historic 

 times ; the burning mountain Mosychlos in the island of 

 Lemnos, which Homer terms the darling seat of He- 

 phaestos, was only destroyed and sunk beneath the waves 

 of the sea, together with the island of Chryse, by the 

 action of earthquake shocks, subsequently to the period 

 of the great Macedonian. (See Kosmos, Bd. i. S. 256 

 and 456, Anm. 9 ; Engl. ed. p. 230 and note 230 ; 

 Ukert, Geogr. der Griechen und Romer, Th. ii. Abth. i. 

 S. 198.) The great and, for almost 1900 years (from 



