424 REACTION OF THE INTERIOR OF THE EARTH 



their mineralogical constitution are like those of Chim- 

 borazo, i.e. consist of a mixture of oligoclase and 

 augite, have thus here broken through granite and 

 mica-slate. Farther to the south, a little to the east 

 of the route from Eiobamba Nuevo to Gruamote and 

 Ticsan, what were formerly called the primitive rocks, 

 mica-slate and gneiss, come everywhere into view in 

 the Cordillera, which has here turned away from the sea, 

 appearing about the foot of the colossal Altar de los 

 Collanes, of Cuvillan, and of the Paramo del Hatillo. 

 Before the arrival of the Spaniards, and even before the 

 sovereignty of the Incas extended so far to the north, 

 the natives are supposed to have worked some metal- 

 liferous beds near the volcano. A little to the south of 

 San Luis, many dikes of quartz may be observed tra- 

 versing a greenish clay-slate. Near Gruamote, at the 

 entrance of the grassy plain of Tiocara, we find great 

 masses of quartzite, very poor in mica, of remarkably 

 linear parallel structure, inclining regularly 70 to the 

 north. More to the south, near Ticsan, not far from 

 Alausi, the Cerro Cuello de Ticsan presents great masses 

 of sulphur in a bed of quartz, subordinate to the adja- 

 cent mica-slate. Such an extensive distribution of 

 quartz in the vicinity of trachytic volcanoes at first 

 sight excites some surprise. But my observations of 

 the superposition, or rather, of the breaking forth of 

 trachyte through mica-slate and granite at the foot of 

 Tungarahua (a phenomenon which is as rare in the 

 Cordilleras as it is frequent in Auvergne), have been 

 confirmed, 47 years later, by the excellent researches of 

 the French geologist, Sebastian Wisse, at Sangay. This 

 colossal volcano, 1343 feet higher than Mont Blanc, 



