64 Prof. Bischof on the Natural History of 



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 fric- 

 tion 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 

 separated by rents, crystals are often found in them, broken 

 through the middle, and both pieces are imbedded in the sepa- 

 rated rocks. Thus, my friend Prof. Noggerath has observed, 

 that many of the larger crystals of glassy felspar in the trachyte 

 of the Drachenjels are broken through in this manner, and 

 that the one piece is displaced several lines from the other. 

 He observed the same phenomenon more frequently in the 

 porphyritic granite near Gopjersgriin in the Fichtelgebirge* 

 The olivine in the basalt of Burzet in Vivarais presents the 

 same appearance, according to Scrope,+ and the separated por- 

 tions of crystals exactly correspond. Faujas observed among 

 the basalts of the bridge of Bridoit adjacent columns, with in- 

 cluded fragments of granite broken through, in consequence of 

 the formation of the columns. All these phenomena prove 

 that these crystalline rocks must have been still soft, after the 

 imbedded crystals had arrived at the stage of perfect solidifica- 

 tion, and that the breaking of the crystals is a consequence 

 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 car- 

 bonate of lime penetrated into the fissures. 



Lastly, instances of the formation of dykes of volcanic mat- 

 ter at the present day, offer a further proof, if further proof be 

 necessary, of their igneous origin, and the accounts given of the 



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

 lisch-statistische Beschreibung des Fichtelbirges, t. ii. p. 114. 



+ Consider, p. 1 36. 



