266 Natural History of Volcanos 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 Noggerath 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 G'op- 

 fersgriln in the Fichtelgehirge.* The olivine in the basalt of 

 Burzet in Vivarais, presents the same appearance, according to 

 Scrope,f 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. 



Lastly, 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 OwliyheeX establish the possibility of 

 eruptions through rents. 



nach Bohmen. Bonn. 1838, p. 171,) in the neighborhood of basalts, and these phe- 

 nomena are so enormous, that they cannot be considered as caused by accidental 

 combustion. 



* Noggerath loco cit. p. 71. See also Goldfuss and Bischof, Physikalisch-statis- 

 tische Beschreibung dcs Fichtelbirges, t. ii, p. 114. 



t Consider, p. 136. X PoggendorfF's Anna!, t. ix, p. 141. 



