430 BEACTION OF THE INTERIOR OF THE EARTH 



are either entirely absent, or, at the utmost, occur only 

 sparingly, and are wholly unessential ingredients. To 

 this division belong the trachytes of the Phlegrsean 

 Fields (Monte Olibano, near Pozzuoli), of Ischia, and of 

 La Tolfa, and also of a portion of the Mont Dore 

 (Grande Cascade). Augite shows itself in small crys- 

 tals in trachytes of the Mont Dore, but only very 

 rarely ( 595 ); in the Phlegrsean fields, with hornblende, 

 not at all ; nor does leucite, of which, however, some 

 pieces were collected by Hoffmann above the Lago 

 Averno (on the road to Cumse), and some by myself on 

 the declivity of the Monte Nuovo( 596 ), in the autumn of 

 1822. Leucite-ophyr, in loose pieces, is more plentiful 

 in the island of Procida and the neighbouring Scoglio 

 di S. Martino." 



Second Division. " The ground-mass contains de- 

 tached crystals of glassy felspar and a quantity of small 

 snow-white crystals of oligoclase. The latter are often 

 intermingled with the glassy felspar, and form a veil 

 round the felspar, as is often the case in Grustav Rose's 

 'granitite' (the rock which forms the main mass of 

 the Riesen- and Iser-gebirge, granite, with red felspar, 

 particularly rich in oligoclase and magnesia-mica ; but 

 without any white potassa mica). Hornblende and 

 mica, and, in some varieties, augite, sometimes present 

 themselves in small quantities. To this class belong 

 the trachytes of the Drachenfelg and Perlenhardt in the 

 Siebengebirge near Bonn ( 597 ), and many varieties of the 

 rocks of Mont Dore and Cantal : also several trachytes 

 in Asia Minor (of which we owe the knowledge to 

 Pierre von Tschichatscheff), at Afiun Karahissar (cele- 

 brated for the culture of the poppy), Mehammed Kjoe 



