NOTES. civ 



( 595 ) p. 430. Rozet, sur les Volcans de 1'Auvergne, in the Mem. de la Soc. 

 Ge'ologique de France, 2eme Se'rie, t. i. p. i. 1844, p. 69. 



( 596 ) p. 430. Fragments of leucite-ophyr, collected by me on Monte Nuovo, 

 have been described by Gustav Rose in Fried. Hoffmann's Geognostischen Beo- 

 bachtungen, 1839, S. 219. On the trachytes of the Monte di Procida, in the 

 island of the same name, and on the rocky shoal of S. Martino, see Roth, Mono- 

 graphic des Vesuvs, 1857, S. 519 522, Tab. viii. The trachyte of the island 

 of Ischia contains, in the Arso or lava-current of Cremate (1301), glassy felspar, 

 brown mica, green augite, magnetic iron, and olivine (S. 528) ; no leucite. 



( 597 ) p. 430. The geologo-topographical relations of the Siebengebirge 

 near Bonn have been developed and described, with generalising sagacity and 

 great exactness, by my friend Berghauptmann H. von Dechen, in the 9th 

 year's series of the Verhandlungen des natur-historischen Vereines der preus. 

 Rheinlande und Westphalens, 1852, S. 289567. All the chemical analyses 

 of the trachytes of the Siebengebirge which have yet appeared are collected there 

 (S. 323 356): and some account is given of the trachytes of the Drachenfels 

 and Rb'ttchen, in which, besides the large crystals of sanidine, many small crys- 

 talline particles can be distinguished in the ground mass. " These were recog- 

 nised by Dr. Bothe, by chemical analyses performed in Mitscherlich's laboratory, 

 to be oligoclase ; in entire agreement with the oligoclase of Danvikszoll (near 

 Stockholm), cited by Berzelius." (Dechen, S. 340 346.) The Wolkenberg 

 and the Stenzelberg are without glassy felspar (357 and 363), and belong not 

 to the second division but to the third; they present a Toluca rock. Many new 

 views are contained in the section of the " Geognostischen Beschreibung des Sie- 

 bcngebirges," which treats of the relative age of trachytic and basaltic conglome- 

 rates (S. 405 461). " Besides the more rare dykes of trachyte, in the trachytic 

 conglomerates, which show that after the deposition of the conglomerate the for- 

 mation of trachyte still continued to take place (S. 413), there are frequent 

 dykes of basalt (416). The formation of basalt decidedly comes down to a later 

 period than that of trachyte, and the principal mass of basalt is here younger 

 than the trachyte. On the other hand, it is only a portion of this basalt, not 

 all basalt (S. 323), which is younger than the great mass of the brown coal. 

 The two formations, basalt and brown coal, run into each other in the Siebenge- 

 birge, as in so many other places, and are to be looked upon, on the whole, as co- 

 temporaneous." Where very small crystals of quartz appear as a rarity in the 

 trachytes of the Siebengebirge, as they do according to Noggerath and Bischof 

 in the Drachenfels and in the Rhondorfer Thai, they fill cavities, and seem to be 

 of later formation (S. 361 and 370) : perhaps they have been produced by the 

 weathering of the sanidine. On Chimborazo I once saw similar but very thin 



