Clvi NOTES. 



depositions of quartz on the sides of the cavities in some very porous brick-red 

 trachytic masses, at an elevation of about 17,000 feet. (Humboldt, Gisement 

 des Roches, 1823, p. 336.) These pieces, which are repeatedly mentioned in 

 my journal, are not in the Berlin collections. Weathering of oligoclase, or of the 

 whole ground-mass of the rock, may also give rise lo such traces of free silicic 

 acid. Some points in the Siebengebirge still deserve fresh and persevering ex- 

 amination. The highest summit, the Lbwenberg, spoken of as basalt, appears, 

 by the analysis of Bischof and Kjerulf, to be a doleritic rock. (H. von Dechen, 

 S. 383, 386, and 393.) The rock of the little Rosenau, which has sometimes 

 been called Sanidophyr, belongs, according to G. Rose, to the first division of his 

 trachytes, and is very nearly related to trachytes of the Ponza Islands. The 

 trachyte of the Drachenfels, with large crystals of glassy felspar, appears to 

 resemble most nearly (according to Abich's observations, which unfortunately 

 are not yet published) that of Dsyndserly dagh, 8500 feet high, which rises 

 to the north of the great Ararat, out of a nummulite formation, having under- 

 lying Devonian strata. 



( W8 ) p. 431. The near vicinity of Cape Perdica, on the island of JEgiua, to 

 the brownish-red Trcezene-trachytes of the peninsula of Methana (Kosmos, Bd. 

 iv. S. 273, Anm. 86 ; English edition, p. 227, and Note 310), and to the sulphur- 

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

 well as those of the island of Kalauria, near the little town of Poros, belong to 

 the same third division of G. Rose (oligoclase, with hornblende and mica). 

 Kurtius, Peloponnesos, Bd. ii. S. 439 and 446, Tab. xiv. 



( 599 ) p. 431. See the excellent geological map of the country round Schem- 

 nitz, by Bergrath Johann von Peltko, 1852, and the Abhandl. der k. k. geolo- 

 gischen Reichsanstalt, Bd. ii. 1855, Abth. i. S. 3. 



C" ) p. 431. Kosmos, Bd. iv. S. 427, Anm. 7 ; English edition, p. 386, 

 and Note 531. 



( M1 ) p. 431. The basaltic columns of Pisoje, the felspathic part of which 

 has been analysed by Francis (Poggend. Annalen, Bd. lii. 1841, S. 471), and 

 which are situated near the bank of the Cauca River, in the plains of Amolanga 

 (not far from the Pueblos de Sta. Barbara and Marmato), consist of a somewhat 

 altered oligoclase in large fine crystals, and small crystals of hornblende. Nearly 

 allied to this mixture are : the quartz-containing diorite-porphyry of Marmato, 

 brought home by Degenhardt, and in which Abich called the felspathic constituent 

 Andesin ; the rock without quartz of Cucurusape, near Marmato, from Boussin- 

 gault's collection (Charles Sainte-Claire Deville, Etudes de Lithologie, p. 29) ; 

 the rock which I found in situ twelve geographical miles east of Chimborazo, 

 under the ruins of Old Riobamba (Humboldt, Kleinere Schriften, Bd. i. S. 161) ; 



