Clxx NOTES. 



( 617 ) p. 439. Gustav Rose, Ueber die zur Granitgruppe gehorigen Gebirgs- 

 arten, in the above-mentioned Journal, Bd. i. 1849, S. 359. 



( 61S ) p. 439. The porphyries of Moran, Real del Monte, and Regla (the 

 latter celebrated on account of the great silver riches of the Veta Biscayna, and 

 the vicinity of the obsidians and pearl-stones of the Cerro del Jacal and Cerro de 

 las Navajas) are, like almost all the metalliferous porphyries of America, entirely 

 without quartz (on these phaenomena, and some completely analogous ones in 

 Hungary, see my Essai geognostique sur le Gisement des Roches, p. 179 188 

 and 190 193); but the porphyries of Acaguisotla, on the road from Acapulco 

 to Chilpanzingo, as well as those of Villalpando to the north of Guanaxuato, 

 which are traversed by auriferous veins, contain, together with sanidine, grains of 

 brownish quartz. As at the Cerro de las Navajas, and in the basalt and pearl- 

 stone-containing Valle de Santiago, along which one passes in going from Valla- 

 dolid to the Volcano of Jorullo, the enclosures of grains of obsidian and glassy 

 felspar in the volcanic rocks are, on the whole, rare, I was the more astonished 

 when, between Capula and Pazcuaro, and especially near Yurisapundaro, I saw- 

 all the ant-hills filled with shining grains of obsidian and sanidine. This was 

 in the month of September 1803. (Nivellement barometr. p. 327, No. 366; 

 and Essai ge'ognost. sur le Gisement des Roches, p. 356.) I wondered how it 

 could be possible for such small insects to carry these minerals from a great 

 distance. I have seen with lively pleasure that an ardent explorer, Jules Mar- 

 cou, has met elsewhere with something quite similar. He says : II existe sur 

 les hauls plateaux des Montagues Rocheuses, surtout aux environs du Fort 

 Defiance (a 1'ouest du Mont Taylor), une espece de fourmis qui, au lieu de se 

 servir de fragmens de bois et de de'bris de vege'taux pour e'lever son edifice, 

 n'emploie que de petites pierres de la grosseur d'un grain de mai's. Son instinct 

 la porte a choisir les fragmens de pierres les plus brillants; aussi la fourmiliere 

 est-elle souvent remplis de grenats transparents magnifiques et de grains de 

 quarz tres-limpides." (Jules Marcou, Resume' explicatif d'une Carte geogn. des 

 Etats Unis, 1855, p. 3.) 



In the present lavas of Vesuvius glassy felspar is very rare ; not so in the 

 older lavas (for example in those of the eruption of 1631), with leucite crystals. 

 Sanidine is also found abundantly, without any leucite, in the Arso-current of 

 Cremate, in Ischia, of the year 1301, which is not to be confounded with 

 the more ancient one described by Strabo, which is near Montagnone and Rotaro. 

 (Kosmos, Bd. iv. S. 340, Anm. 61, and S. 447 ; English edition, p. 260, Note 

 385, and p. 407.) Glassy felspar is not found in the trachytes of Cotopaxi, or 

 the other volcanoes of the Andes : nor does it appear in the subterranean pumice- 



