ON ITS EXTERIOR. VOLCANOES. 423 



some point at which it might be clearly seen what was 

 the older rock upon which the mighty cones and bell- 

 shaped mountains rose, or, more properly speaking ? 

 through which they had broken forth. I was so fortu- 

 nate as to find such a point, at a height of 9483 feet 

 above the Pacific, in the month of June 1802, when 

 attempting, from Eiobamba Nuevo, the ascent of Tun- 

 gurahua, on the side of the Chuchilla de Gruandisava. I 

 was proceeding from the pleasantly situated village of 

 Penipe, by the oscillating rope-bridge (puente de ma- 

 roma) over the Eio Puela, to the solitary Hacienda de 

 G-uansce (7929 feet), where, on the south-east, opposite 

 to the junction of the Eio Blanco with the Eio Chambo, 

 a magnificent colonnade of black, pitchy-looking trachyte 

 rises to view. The appearance recalls that of the ba- 

 saltic quarry at Unkel seen from a distance. On the 

 Chimborazo, rather above the little lake of Yana Cocha, 

 I saw a similar, loftier, but less regular columnar group 

 of trachyte. The columns to the south-east of Penipe 

 are, for the most part, five-sided, only 15 inches in 

 diameter, and often bent and diverging. At the foot of 

 these pitch-black Penipe trachytes (not far from the 

 mouth of the Eio Blanco), one sees a phenomenon very 

 unlooked for in this part of the Cordilleras, viz., green- 

 ish-white mica-slate, with interspersed garnets; and, 

 farther on (beyond the shallow little stream of Basca- 

 guan, by the Hacienda of Gruansce, near the bank of 

 ihe Eio Puela), probably dipping under the mica-slate, 

 granite of a middling-sized grain, with bright reddish 

 felspar, a little blackish-green mica, and much grayish- 

 white quartz. Hornblende is wanting. It is not syenite. 

 The trachytes of the volcano of Tungurahua, which in, 



