148 SOUTH AMERICA— THE ANDES REGIONS. 



In 1869 another eruption filled the bed of the Cauca with mud and pumice, 

 and completely obstructed the stream for some time. A rivulet flowing from the 

 slopes of a parasitic cone tumbles over a superb cascade 260 feet high. This is 

 the famous Pasambio, or " Vinegar Eiver," which, according to Boussingault, 

 annually liberates 17,000 tons of sulphuric acid, and 15,000 of hydrochloric 

 acid. 



Purace forms the north-west termination of the snowy five-peaked Coconucos 

 chain, south of which extend the Buey plateau and a large group of heights and 

 paramos collectively known as the " Mass of Colombia." Here is the true hydro- 

 graphic centre of the country, where rise the four great rivers Patia, Cauca, 

 Mao-dalena, and Caqueta, this last a main headstream of the Amazons. The ridge 

 separating the upper Patia and upper Cauca waters is surmounted at its northern 

 extremity by the extinct Sotara volcano (14,500 feet), which presents an imposing 

 aspect, thanks to its isolation and to its bare gloomy rocks, contrasting with the 

 surrounding forest-clad heights. 



South of the Colombia group the three main Cordilleras converge in the 

 Pasto " knot," near which rise the three volcanoes of Bordoncillo (Patascoi), and 

 Campanero (12,470 feet), at the foot of which lies the lacustrine Cocha basin, 

 draining through the Putumayo to the Amazons, and lastly the Pasto (14,000 

 feet), which gives its name to the whole group, and which is itself named from its 

 extensive pasturages. From the vast crater of the Pasto flows a stream charged 

 with acids, like the Vinegar River, but three times more copious. During the 

 frequent eruptions of this volcano fragments of incandescent rocks are often 

 hurled to a great height. 



South of Pasto towards the Ecuador frontier follow other volcanoes, such as 

 the Azufral (13,360 feet), the Cumbal (15,720), and the Chiles (15,680), which 

 already stand in the main axis of the Choco or Western Cordillera, the third great , 

 Andean chain of Colombia. The Azufral crater is at present flooded by a deep 

 emerald-green lake, while sulphurous vapours in a state of combustion flit over 

 the snowy crest of Cumbal. 



The "Western Cordillera. 



Like the other Cordilleras, the western range consists of a central crystalline 

 backbone underlying cretaceous formations ; but no igneous cones occur anywhere 

 in the section extending from the plains of the Atlantic coast to the banks of the 

 Rio Patia. Excluding the low Maria chain between the lower Magdalena and 

 the sea, the Choco system proper begins with the heights enclosing the Rio Sinu 

 basin. Eastwards are grouped the Murrucucu Mountains, which are prolonged 

 south-westwards by the San Jeronimo chain, while on the west rise the Quinamari 

 plateaux, whence a range of heights runs north-west to the Aguila headland at 

 the eastern entrance of the Gulf of Uraba. Here the Chigurrado peak attains a 

 height of over 6,500 feet. 



The various ramifying branches at the extremity of the cordillera converge in 

 the Paramillo (11,120 feet), between the Cauca and the upper Rio Leon valley. 



