Natural History of Volcanos and Earthquakes. ' 267 



If alterations in the adjacent rocks, or other phenomena already 

 mentioned, are not observed, we may infer that the elevations 

 have taken place in a solid state. Notwithstanding this solidity, 

 the highly elastic and exceedingly hot vapors may certainly cause 

 considerable chemical alterations in the elevated masses, as well 

 as in the adjacent rocks. 



It is impossible to determine any regular order of succession in 

 the elevation of the pyrogenetic rocks. They occur in every pe- 

 riod of the stratified formations. Older ones have very commonly 

 received those of more recent date into their fissures. There 

 scarcely exists a single unstratified rock which is not somewhere 

 to be found filling up dykes in granite. Basalt-dykes traverse 

 many unstratified rocks, such as trachyte, conglomerate, and oth- 

 ers. In Iceland J tufa is found alternating with slaggy lava ; and 

 dykes of a porous trachytic rock traverse the tufa of Stromboli 

 and Vulcanello in the Lipari Isla?ids, &c.* 



Masses of melted matter will break through the bottom of the 

 sea more easily, because resistance is there the least considerable. 

 To this may be ascribed the frequent elevation of islands from 

 the bottom of the sea, not only in historical times, but also at the 

 present day, and under the eyes of observers, in whom the ut- 

 most confidence may be placed. The most extraordinary and 

 instructive island in this respect is Santorin, because it unites 

 the whole history of volcanic islands and islands of elevation. A 

 more beautiful, regular, and perfect crater or elevation is not to be 

 found, than in the space which is almost entirely surrounded by 

 the inner circle oi Sa7itorin (which encompasses more than one- 

 half of it) and by its continuation as exhibited in the islands of 

 Therasia and Aspronisi.\ Here it is probable that the clay-slate 

 was broken through and upraised. These islands, therefore, form 

 an inseparable whole, and cannot have been raised one after an- 

 other. On the other hand, history and tradition inform us, that 

 nature has never ceased in its endeavors to create a volcano in the 

 centre of this crater of elevation. One hundred and eighty four 

 years before the birth of Christ, the Island of Hiera (now called 



* De la Beche, Handbuch der Geognosie Von v. Dechen. Berlin, 1832. Absch- 

 nitt xi. 



t Von Buch in Poggendorf's Annal. v. x, p. 172. See the drawing in his splen- 

 did atlas, and the sketch in these Annal. v. xxiv, p. 1. 



