302 COSMOS. 



interest for us was the finding of several white fragments, 

 three or four inches in diameter, of a rock rich in feldspar 

 baked into the black basaltic lava. I regarded these at first* 

 as syenite, but from the exact examination by Gustav Rose, 

 of a fragment which I brought with me, they probably belong 

 rather to the granite formation, which Burkart has also seen 

 emerging from below the syenite of the Rio de las -Balsas. 

 "The inclosure is a mixture of quartz and feldspar. The 

 blackish-green spots appear to be not hornblende, but mica 

 fused with some feldspar. The white fragment baked in is 

 split by volcanic heat, and in the crack white, tooth-like, 

 fused threads run from one margin to the other." 



To the north of the great volcano and the scoriaceous lava 

 mountain which it has vomited forth in the direction of the 

 old basalt of the Cerro delMortero follow the two last of the 

 six often-mentioned eruptions. These hills also were original- 

 ly very active, for the people still call the extreme mountain 

 of ashes EL Volcancito. A broad fissure, open toward the west, 

 bears the traces of a destroyed crater. The great volcano, 

 like the Epomeo in Ischia, appears to have only once poured 

 out a mighty lava stream. That its lava-pouring activity 



* " M. Bon plan d and myself were particularly astonished at finding, 

 encased in the basaltic, lithoid, and scorified lavas of the volcano of 

 Jorullo, white or greenish-white angular fragments of syenite, com- 

 posed of a little amphibole and a great quantity of lamellar feldspar. 

 Where these masses have been split by heat the feldspar has become 

 filamentous, so that the margins of the crack are united in some places 

 by fibres elongated from the mass. In the Cordilleras of South Amer- 

 ica, between Popayan and Almaguer at the foot of the Cerro Bronco- 

 so, I have found actual fragments of gneiss encased in a trachyte 

 abounding in pyroxene. These phenomena prove that the trachytic 

 formations have issued from beneath the granitic crust of the globe. 

 Analogous phenomena are presented by the trachytes of the Siebenge- 

 lirge on the banks of the Rhine, and by the inferior strata of Phono- 

 lite (Porphyrs chief er) of the Biliner Stein in Bohemia." (Humboldt, 

 Essai Geognostique sur le Gisement des Roches, 1823, p. 133 and 339.) 

 Burkart also (Anfenthalt und Reisen in Mexico, bd. i., s. 230) detected 

 inclosed in the black lava, abounding in olivin, of Jorullo, " blocks of 

 a metamorphosed syenite. Hornblende is rarely to be recognized dis- 

 tinctly. The blocks of syenite may certainly furnish an incontroverti- 

 ble proof that the seat of the focus of the volcano of Jorullo is either 

 in or below the syenite, which shows itself in considerable extent, a 

 few miles (leguas) farther south, on the left bank of the Rio de las 

 Balsas, flowing into the Pacific Ocean." Dolomieu, and, in 1832, the 

 excellent geognosist, Friedrdch Hoffmann, found in Lipari, near Cane- 

 to, fragments of granite, formed of pale red feldspar, black mica, and 

 a little pale gray quartz, inclosed in compact masses of obsidian (Pog- 

 gendorff s Annalen der Physik, bd. xxvi., s. 49). 



