ON ITS EXTERIOK. VOLCANOES. 433 



S. 353.) I brought such a piece with distinct uralite 

 crystals back with me from a height of 13,300 feet on 

 the side of Tunguragua. In Grustav Rose's opinion, it 

 is strikingly different from the seven trachyte fragments 

 from the same volcano which are in my collection, and 

 reminds him of the formation of schistose augitic por- 

 phyry which we found so extensively on the Asiatic 

 slope of the Ural. (See the last-quoted work, Bd. ii. 

 S. 544.) 



Fifth Division. "A mixture of labradorite ( 605 ) and 

 augite ( 606 ) ; a doleritic trachyte. Etna, Stromboli, and, 

 according to the excellent examination of the trachytes 

 of the Antilles by Charles Sainte-Claire Deville, the 

 Soufriere de la Guadeloupe, and on Bourbon the three 

 great ( Cirques ' which surround the Pic de Salazu." 



Sixth Division. "An often-grey ( ground-mass,' in 

 which there are crystals of leucite and augite with very 

 little olivine : Vesuvius and Somma ; also the extinct 

 volcanoes of Vulturo, Eocca Monfina, the Alban Hills 

 and Borghetto. In the older masses, (for example in 

 the masonry and pavement of Pompeii,) the leucite 

 crystals are of considerable size and more abundant 

 than the augite. On the other hand in the present 

 lavas the augites prevail, and generally speaking leucites 

 are very rare. Nevertheless the stream of lava of April 

 22, 1845, furnished them in large quantities. ( 607 ) Frag- 

 ments of trachytes belonging to the first division, 

 containing glassy felspar (Leopold von Buch's ' trachytes 

 proper'), are found imbedded in the tufas of Monte 

 Somma ; and also singly beneath the layer of pumice 

 which covers Pompeii. The leucite-ophyr trachytes of 

 this sixth division are to be carefully distinguished from 



VOL. IV. F P 



