Natural History of Volcanos and Earthquakes. 267 
- Ifalterations 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- 
od 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 
'0 be found filling up dykes in granite. Basalt-dykes traverse 
many unstratified rocks, such as trachyte, conglomerate, and oth- 
es. In Iceland, tufa is found al ternating with slaggy lava; and _ 
dykes of a porous trachytic rock traverse the tufa of Strombol . 
and Vuleanello in the Lipari Islands, &c.* 3 
Masses of melted matter will break through the bottom of the 
sea more easily, because resistance is there the least considerable. 
© this may be ascribed the frequent elevation of islands from 
the bottom of the sea, not only in historical times, but also at the 
Mesent 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 voleanic islands and islands of elevation. A 
ore beautiful, regular, and perfect crater or elevation is not to be 
ound, than in the space which is almost entirely surrounded by 
the inner circle of Santorin (which encompasses more than one- 
half of it) and by its continuation as exhibited in the islands of 
asia and Aspronisi.t Here it is probable that the clay-slate 
Was broken through and upraised. 'These islands, therefore, form 
1 inseparable whole, and cannot have been raised one after an- 
other. On the other hand, history and tradition inform us, that 
Mature has never ceased in its endeavors to create a volcano in the 
“entre of this crater of elevation. One hundred and eighty four 
Yeats before the birth of Christ, the Zsland of Hiera (now called 
a. ee 
sg la Beche, Handbuch der Geognosie Von v, Dechen. Berlin, 1932. Absch- 
itt xj, 
i Von Buch in Poggendorf’s Annal. v. x, p- 172. See the drawing in his splen= 
: atlas, and the sketch in these Annal. v. xxiv, p. 1. 
