TRUE VOLCANOES. 317 



when the summit was on all sides perfectly free from clouds. 

 On the 16th of March, 1802, Bonpland, Carlos Montufar, 

 and myself reached a ridge of rock covered with pumice- 

 stone, and black, basaltic scoriae in the region of perpetual 

 snow, at an elevation of 2837 toises (18,142 feet), and con- 

 sequently, 2358 feet higher than Mont Blanc. The snow 

 was firm enough to bear us on many points near the ridge of 

 rock, which is so rare under the tropics (temperature of the 

 atmosphere 28'8 34 0< 5). On the southern declivity, which 

 we did not ascend, at the Piedro de Azufre, where scales of 

 rocks sometimes separate of themselves by weathering, masses 

 of pure sulphur, of 10 12 feet in length and 2 feet in thick- 

 ness, are found ; sulphurous springs are wanting in the vi- 

 cinity. 



Although in the eastern Cordillera the volcano of Anti- 

 sana, and especially its western declivity (from Ansango and 

 Pinantura, toward the village of Pedregal), is separated from 

 Cotopaxi by the extinct volcano of Passuchoa* with its wide- 

 ly distinguishable crater (La Peila), by the Nevado Sinchula- 

 hua and by the lower Ruminaui, there is still a certain re- 

 semblance between the rocks of the two giants. From Quin- 

 che onward the whole eastern chain of the Andes has pro- 

 duced obsidian, and yet El Quinche, Antisana, and Passuchoa 

 belong to the basin in which the city of Quito is situated ; 

 while Cotopaxi bounds another basin, that of Lactacunga, 



* Passuchoa, separated by the farm El Tambillo from the Atacazo, 

 does not any more than the latter attain the region of perpetual snow. 

 The elevated margin of the crater, La Peila, has fallen in toward the 

 west, but projects toward the east like an amphitheatre. The tradi- 

 tion runs that at the end of the 16th century the Passuchoa, which 

 had previously been active, ceased its manifestations of activity on 

 the occasion of an eruption of Pichincha, which proves the communi- 

 cation between the vents of the opposite eastern and western Cordil- 

 leras. The true basin of Quito, closed like a dam on the north by 

 a mountain group between Cotocachi and Imbaburo, and on the south 

 by the Altos de Chisinche (between 20' N. and 41' S-), is for the 

 most part divided longitudinally by the mountain ranges of Ichimbio 

 and Poingasi. To the eastward lies the valley of Puembo and Chillo ; 

 to the westward the plain of Inaquito and Turubamba. In the eastern 

 Cordillera follow from north to south Imbaburo, the Faldas de Gua- 

 mani, and Antisana, Sinchulahua, and the perpendicular black wall, 

 crowned with turret-like points, of Ruminaui (Stone-eye); in the 

 western Cordillera, Cotocachi, Casitagua, Pichincha, Atacazo, and Co- 

 razon, upon the slopes of which blooms the splendid Alpine plant, the 

 red Ranunculus Gusmani. This has appeared to me to be the place to 

 give, in brief terms, a morphological representation, drawn from my 

 own experience, of the form of a spot which is so important and classic- 

 al in respect to volcanic geology. 



