COSMOS. 



grsean Fields (Monte Olibano near Pozzuoli), that of Ischia 

 and of La Tolfa, as also a part of tlie Mont-Dore (the Grande 

 Cascade). A ugite is but very rarely found in small crystals 

 in trachytes of the Mont-Dore 71 never, in the Phlegrsean 

 Fields together with hornblende ; nor is leucite, of which 

 last however, Hoffmann collected some pieces on the Lago 

 Averno (on the road to Cuinse), while I found some on the 

 slope of the Monte Nuovo 72 (in the autumn of 1822). 

 Leucite-ophyr in loose fragments is more frequent in the 

 island of Procida and the adjoining Scoglio di S. Martino." 



Second Division. " The ground-mass contains some de- 

 tached crystals of glassy felspar, and a profusion of small 

 snow-white crystals of oligoclase. The latter are frequently 

 overspread with the glassy felspar in regular order, and 

 form a covering about the felspar, as is so frequently seen 

 in G. Hose's granitite (the principal mass of the Eiesen- 

 gebirge and Iser-gebirge, consisting of granite with red 

 felspar, particularly rich in oligoclase and magnesian-mica, 

 but without any white potash-mica). Hornblende and mica, 

 and in some modifications augite, occasionally appear in 

 small quantity. To this division belong the trachytes of the 

 Drachenfels and of the Perlenhardt in the Siebengebirge 73 

 near Bonn, and many modifications of the Mont-Dore and 

 Cantal ; some trachytes also of Asia Minor (for which we 

 are indebted to that industrious traveller Peter von Tschi- 



71 Eozet, Sur les montagnes de 1'Auvergne, in the Mem. de la Soc. 

 Geol.de France, 2me SeVie, t. i, partie i, 1844, p. 69. 



72 Fragments of Leucite-ophyr, collected by me at the Monte Nuovo, 

 are described by Gustav Hose in Fried. Hoffmann's Geoynosticheii Beo- 

 backtungen, 1839, s. 219. On the trachyte of the Monte di Procida of 

 the island of the same name, and the rock of San Martino, see Roth, 

 Monographic des Vesuvs. 1857, s. 519 522, tab. viii. The trachyte of 

 the island of Ischia contains in the Arso, or stream of Cremate (1301) 

 vitreous felspar, brown mica, green augite, magnetic iron and olivine 

 (s. 528), but no leucite. 



73 The geologico-topographical conditions of the Siebengebirge near 

 Bonn, have been developed with comprehensive talent and great exact- 

 ness by my friend H. von Dechen, director of mines, in the 9th annual 

 volume of the Verhandlungcn des Naturhistorischen Vereines der Preuss, 

 RkcMandeund Westphalens, 1852, s. 289567. All the chemical ana- 

 lyses of the trachytes of the Siebengebirge which hf>ve hitherto ap- 

 peared are there collected (p. 323 356); mention is also made of the 

 trachytes of the Drachenfels and Rottchen, in which, besides the large 

 crystals of sanidine, several small crystalline particles may be distm- 



