RICHTOFEN ERUPTIVE ROCKS. 33 



On the Tertiary Eruptive Hocks of Hungary and Transylvania. 

 By Baron Bichtofen. 



[Proceed. Imp. Geol. Instit. Vienna, April 24, I860.] 



The eruptive region extending from Persia, over Asia Minor and 

 Hungary, to the Siebengebirge and the Eifel on the Bhine, is repre- 

 sented on the south slope of the Carpathians by seven distinct 

 groups, either concentrated into masses, or spreading in long ranges. 

 These groups are, 1st, the Schemnitz Mountains ; 2ndly, those of 

 Visegrad, broken through by the Danube between Gran and Waitzen ; 

 3rdly, the Matra ; 4thly, the Tokay-Epesies group ; 5thly, the Hun- 

 garian ; 6thly, the Transylvanian Vihorlet-Gatin (the second known 

 under the special name of Hargitta) ; and, 7thly, the metalliferous 

 mountains of Transylvania. The materials of all these mountains, 

 which, from their prevailing constituents, may be comprised under 

 the general designation of traehytic rocks, exhibit, as does the great 

 European-Asiatic range, in its totality, three distinctly limited 

 groups: — 1. the Rhyolitic ; 2. the Traehytic; and 3. the Basaltic 

 group ; the last of them being, as it seems, exclusively represented 

 by Basalts ; the occurrence of Phonolites, Dolerites, and other ana- 

 logous rocks having not yet been duly ascertained. 



The second group is by far the most prevalent, being nearly 

 exclusively represented by amphibolous oligoclastic varieties, vitreous 

 felspar (sanidine^ being only conspicuous in some subordinate eruptions 

 of more recent date. Silica is never abundant enough to appear in 

 independent secretions. There exists a double parallel series, of 

 greenstone -trachytes, on the one, and of grey trachytes on the other 

 side, both being compounds of amphibole and oligoclase, subordinately 

 including augite, whenever silica is diminishing. The greenstone- 

 trachytes are characterized by an abundance of metalliferous minerals, 

 by their easy decomposition, their peculiar outlines, and their geo- 

 logical age, being constantly of older age than the grey trachytes. 

 The same peculiarities have been observed in the trachytes of Asia 

 Minor and Mexico ; their real cause, however, still remains unknown. 



The designation of " rhyolitic group " is proposed for the totality 

 of the most eminently siliciferous among the eruptive rocks of com- 

 paratively less remote date, being equivalent to the quartziferous 

 and non- quartziferous eruptive porphyries among the older por- 

 phyritic rocks. The excess of silica, generally seoreted in the shape 

 of quartz-crystals, gradually diminishes, and at last completely 

 disappears. Beyond this limit the rhyolitic group continues through 

 a series of sanidine rocks, with accessory presence of oligoclase. 

 Although chemically and mineralogically the transition of rhyolite 

 into trachyte may become so imperceptible, that, in some cases, 

 band-specimens may leave some doubt concerning their real nature, 

 both these groups, in the Hungarian mountains, are so distinctly 

 characterized, that any geologist observing them in situ cannot bo 

 perplexed about them. Bcudant applied to certain varieties the 

 designations of "traehytic porphyry," "perlite," and "millstone- 

 porphyry," which Abich comprised under the general category of 



