TRUE VOLCANOES. 425 



and many modifications of the Mont Dore and Cantal ; some 

 trachytes also of Asia Minor (for which we are indebted to 

 that industrious traveler Peter von Tschichatscheff), of Afi- 

 un Karahissar (famous for the culture of the poppy) and Me- 

 hammed-kyoe in. Phrygia, and of Kayadschyk and Donan- 

 lar in Mysia, in which glassy feldspar, with a great deal of 

 oligoclase, some hornblende, and brown mica, are mingled." 

 Third Division. — "The ground mass of this dioritic tra- 

 chyte contains many small crystals of oligoclase, with black 

 hornblende and brown magnesia mica. To this belong the 

 trachytes of iEgina,* of the valley of Kozelnik, near Schem- 



prove that the formation of trachyte has still continued after the de- 

 posit of the conglomerate (s. 413), are associated a great number of ba- 

 salt courses (s. 41G), The basalt formation extends decidedly into a 

 later basalt than the trachyte formation, and the principal mass of the 

 basalt is here more recent than the trachyte. On the other hand, a 

 portion of this basalt only, and not of all basalts (s. 323), is more re- 

 cent than the great mass of the brown-coal rocks. Both formations, 

 the basalt and the brown-coal rocks, run into each other in the Sie- 

 bengebirge, as well as in many other places, and must be considered 

 in the aggregate as contemporaneous." Where very small crystals of 

 quartz occur by way of rarity in the trachytes of the Siebengebirge, as 

 (according to Noggerath and Bischof ) in the Drachenfels and in the 

 valley of Rhondorf, they fill up cavities and seem to be of later forma- 

 tion (p. 361 and 370) ; caused perhaps by efflorescence of the sanidine. 

 On Chimborazo I have on one solitary occasion seen similar deposits 

 of quartz, though very thin, on the internal surfaces of the cavities of 

 some very porous, brick-red masses of trachyte at an elevation of 

 about 17,000 feet (Humboldt, Gisement des Roches, 1823, p. 336). 

 These fragments, which are frequently mentioned in my journal, are 

 not deposited in the Berlin collections. Efflorescence of oliglocase, or 

 of the whole fundamental mass of the rock, may also yield such traces 

 of disengaged silicic acid. Some points of the Siebengebirge still 

 merit renewed and persevering investigation. The highest summit, 

 the Lowenburg, represented as basalt, seems, from the analyses of 

 Bischof and Kjerulf, to be a doleritic rock (H. v. Dechen, s. 383, 386, 

 393). The rock of the little Rosenau, which has sometimes been called 

 sanido-phyre, belongs, according to G. Rose, to the first division of his 

 trachytes, and is very closely allied to many of the trachytes of the 

 Ponga Islands. The trachyte of the Drachenfels with large crystals 

 of glassy feldspar seems, according to Abich's yet unpublished investi- 

 gations, most nearly to resemble the Dsyndserly-dagh, which rises to a 

 height of 8526 feet, to the north of the great Ararat, from a formation 

 of nummulites under-dipped by Devonian strata. 



* From the close propinquity of Cape Perdica, of the island of 

 iEgina, to the long famous red-brown Trozen-trachvtes ( Cosmos, see 

 above, p. 219) of the peninsula of Methana, and from the sulphur 

 springs of Bromolimni, it is probable that the trachytes of Methana, as 

 well as those of the island of Kalauria, near the small town of Poros, 

 belong to the same third division of Gustav Rose (oligoclase with horn- 

 blende and mica) (Curtius, Pcloj>o?inesos, bd. ii., s. 439, 4-16, tab. xiv.). 



