TRUE VOLCANOES. 337 



many points near the ridge of rock, which is so rare under 

 the tropics (temperature of the atmosphere, 28 0> 8 34'5). 

 On the southern declivity, which we did not ascend, at the 

 Piedro de Azufre, where scales of rock sometimes separate 

 of themselves by weathering, masses of pure sulphur of 

 10 12 feet in length, and 2 feet in thickness, are found; 

 sulphurous springs are wanting in the vicinity. 



Although in the eastern Cordillera the volcano of Anti- 

 sana, and especially its western declivity (from Ansango 

 and Pinantura, towards the village of Pedregal) is sepa- 

 rated from Cotopaxi by the extinct volcano of Passuchoa 2 ' 

 with its widely distinguishable crater (la Peila), by the 

 Nevado Sinchulahua and by the lower Ruminaui, there is 

 still a certain resemblance between the rocks of the two 

 giants. From Quinche onwards the whole eastern chain 

 of the Andes has produced obsidian, and yet el Quinche, 

 Antisana, and Passuchoa belong to the basin in which the 

 city of Quito is situated ; whilst Cotopaxi bounds another 

 basin, that of Lactacunga, Hambato and Riobamba. The 

 small knot of mountains of the Altos of Chisinche sepa- 

 rates the two basins like a dam ; and what is remarkable 



' x 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 towards the 

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

 tion runs that at the end of the sixteenth 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 Cordilleras. 

 The true basin of Quito, closed like a dam, on the north by a moun- 

 tain 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 ridges 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 

 Guamani, and Antisana, Sinchulahua, and the perpendicular, black 

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

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

 Corazon, 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 

 owii experience, of the form of a spot which is so important and 

 classical in respect to volcanic geology. 



VOL. V. Z 



