266 Natural History of Voleanos and Earthquakes. 
The conglomerates which frequently surround these volcanic 
masses, and which are not confined to the basalts and trachytes, 
but are also found accompanying the greenstones, porphyries, and 
granites, Von Buch considers to be produced by the friction of the 
rising matter against the rock; and their existence is a further 
proof of the pyrogenetic origin of these masses. 
Other phenomena lead us also to infer that crystalline rocks 
have risen in a melted state. If, for instance, such rocks are sep- 
arated by rents, crystals are often found in them, broken through 
the middle, and both pieces are imbedded in the separated rocks. 
Thus, my friend Prof. Néggerath has observed, that many of the 
larger crystals of glassy felspar in the trachyte of the Drachenfels 
are broken through in this manner, and that the one piece is dis- 
placed several lines from the other. He observed the same phe- 
nomenon more frequently in the porphyritic granite near Gop- 
fersgriin in the Fichtelgebirge.* The olivine in the basalt of 
Burzet in Vivarais, presents the same appearance, according to 
Scrope,t and the separated portions of crystals exactly correspond. 
Faujas observed among the basalts of the bridge of Bridon adja- 
cent columns, with included fragments of granite broken through, 
in consequence of the formation of the columns. All these phe- 
nomena prove that these crystalline rocks must have been still 
soft, after the imbedded crystals had arrived at the stage of per- 
fect solidification, and that the breaking of the crystals is a con- 
sequence of cooling. 
‘The occurrence of arragonite in the fissures and cavities of 
crystalline rocks, basalt, for instance, seems also, according to the 
above-mentioned experiments of G. Rose, to prove, that these 
rocks were at least still hot, when cold solutions of carbonate of 
lime penetrated into the fissures. . 
astly, instances of the formation of dykes of volcanic matter 
at the present day, offer a further proof, if further proof be necces 
sary, of their igneous origin, and the accounts given of the recent 
eruptions at Ponohohoa in Owhyhee,{ establish the possibility of 
eruptions through rents. : 
rca a 
nach Béhmen. Bonn. 1838, p. 171,) in the neighborhood of basalts, and these ie 
nomena are so enormous, that they cannot be considered as caused by acciden 
combustion. . 
* Noggerath loco cit. p. 71. Sce also Goldfuss and Bischof, Physikalisch-sta® 
tische Beschreibung des Fichtelbirges, t. ii, p. 114. 
t Consider. p. 136. } Poggendorff’s Annal, t. ix, p- ial, 
