TRUE VOLCANOES. 445 



side of the Cucliilla de Guandisava. I proceeded from the 

 delightful village of Penipe over the swinging rope-bridge 

 (puente de maroma) of t'he Rio Puela to the isolated Ha- 

 cienda de Guansce (7929 feet), where to the south-east, op- 

 posite the point at which the Rio Blanco falls into the Rio 

 Chambo, rises a splendid colonnade of black trachyte resem- 

 bling pitch-stone. It looks at a distance like the basalt- 

 quarry at Unkel. At Chiruborazo, a little higher than the 

 basin of Yana-Cocha, I saw a similar group of trachytic 

 columns of greater height but less regularity. The columns to 

 the south-east of Penipe are mostly pentagonal, only 14 inches 

 in diameter, and frequently bent and diverging. At the foot 

 of this black trachyte of Penipe, not far from the mouth of 

 the Rio Blanco, a very unexpected phenomenon presents 

 itself in this part of the Cordilleras j greenish- white mica- 

 slate with garnets interspersed in it, and farther on, beyond 

 the shallow stream of Bascaguan, at the hacienda of Guansce, 

 near the shore of the Rio Puela, and probably dipping be 

 low the mica-slate granite of a middling-sized grain, with 

 light reddish felspar, a small quantity of blackish green mica 

 and a great deal of greyish white quartz. There is no horn- 

 blend, nor is there any syenite. Thus it appears that the 

 trachytes of the volcano of Tungurahua, resembling those 

 of Chimborazo in their mineralogical condition, that is to 

 say, consisting of a mixture of oligoclase and augite, 

 have here penetrated granite and mica-slate. Farther 

 towards the south, and a little to the east of the road 

 leading from Riobamba Nuevo to Guamote and Ticsan, in 

 that part of the Cordilleras which recedes from the sea-shore, 

 the rocks formerly called primitive, mica-slate and gneiss, 

 make their appearance everywhere, towards the foot of the 

 colossal altar de los Collanes, the Cuvillan, and the Paramo 

 del Hatillo. Previous to the arrival of the Spaniards; and 

 even before the dominion of the Incas extended so far to the 

 north, the natives are. said to have worked metalliferous 

 beds in the neighbourhood of the volcanoes. A little to the 

 south of San Luis numerous dykes of quartz are observed 

 running through a greenish clay-slute. At Guamote, at the 

 entrance to the grassy-plain of Tiocaxa, we found large masses 

 of rock consisting of quartzites very poor in mica, of a dis- 

 tinct linear parallel structure, running reg^arly at an angle 



