TRUE VOLCANOES. 321 



exact examination by Gustav RO-SP, of a fragment which I 

 brought with me, they prohably belong rather to the granite 

 formation, which Bnrkart has also seen emerging from 

 below the syenite of the Rio de las Balsas. " The inclosure 

 is a mixture of quartz and felspar. The blackish green spots 

 appear to be not hornblende, but mica fused with some 

 felspar. 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 del Mortero, follow the two 

 last of the six often-mentioned eruptions. These hills also 

 were originally very active, for the people still call the ex- 

 treme mountain of ashes, el Volcancito. -A. broad fissure 

 opened towards the west, bears the traces of a destroyed 

 crater. The great volcano, like the Epomeo in Ischia, ap- 

 pears to have only once poured out a mighty lava-stream. 

 That its lava-pouring activity endured after the period 01 

 its first eruption, is not proved historically ; for the valuable 

 letter, so happily discovered, of Father Joaquin de Ansogorri, 

 written scarcely three weeks after the first eruption, treats 

 almost exclusively of the means of making " arrangements 

 for the better pastoral care of the country people who had 

 fled from the catastrophe and become dispersed ;" and for the 

 following thirty years we have no records. As the tradition 

 speaks very generally of fires which covered so great a sur- 

 face, it is certainly to be supposed that all the six hills upon 

 the great fissure, and the portion of the Malpais itself in 

 which the Hornitos have appeared, were simultaneously in 

 combustion. The temperature of the surrounding air, which 

 I measured, allows us to judge of the heat which prevailed 

 there 43 years previously ; they remind one of the former 

 condition of our planet, in which the temperature of its 

 atmospheric envelope, and with this the distribution of 

 organic life, might be modified by the thermic action of the 

 interior by means of deep fissures (under any latitude and 

 for long periods of time). 



Caneto, fragments of granite, formed of pale red felspar, black mica, 

 and a little pale gray quartz, enclosed in compact masses of obsidiau 

 (Poggendorfl's Annalen der Physik, Bd. xxvi, s. 49). 



VOL. V. Y 



