4 ME. J. A. DOUGLAS OX GEOLOGICAL SECTIONS [April 1914,. 



over the Eastern Cordillera into the district known as the North 

 Yungas. 



This railway commences at the port of Arica, which is situated 

 in lat. 18° 29 S. and long. 70° 20' W., just at the point where the 

 main trend of the Pacific coast-line of South America changes 

 from a north-and-south direction to north-west by south-east. 

 After following the shore for a few miles, it turns inland up the 

 fertile valley of the Llutah River to Poconchile (kilometre 37 ; 

 altitude 1772 feet). 



From this point a steep winding ascent is made over desert foot- 

 hills and the so-called ' Pampa Colorada ' to Central (kilom. 70 ; 

 alt. 4859 feet) ; it is continued eastwards with increasing grades 

 and a 40-kilometre stretch of rack-and-pinion line, over typical 

 1 bad lands ' composed of numerous small and steep-sided dry rocky 

 valleys or quebradas, until more or less level ground is reached 

 above Huaylas (kilom. 135 ; alt. 12,797 feet). We are here in the 

 region of the Western Cordillera, a vast range of giant extinct 

 volcanoes which rise abruptly from the high-level plateau. 



On the south are visible the mighty peaks of Sajama (21,423 

 feet) and the Payachatas or Twins ; while close at hand, separated 

 from us by the deep Jamiraya gorge, through which flow the head- 

 waters of the Llutah River, stands the ' Nevada de Putre ' or- 

 Taapaca (19,145 feet) ; see PI. I. 



Following the line past the swamps of Ancachulpa and the salt 

 lake Laguna Blanca to the Bolivian frontier, we pass in close 

 proximity to the southern base of Mount Tacora (19,520 feet) ; 

 while Mount Chupiquina (18,855 feet) and other high peaks are 

 seen succeeding one another in the north. 



After crossing the frontier (kilom. 205 ; alt. 13,321 feet), the 

 railway makes a gradual descent to the valley of the Mauri River 

 (kilom. 250 ; alt. 12,842 feet), which is followed for some 50 miles 

 until it enters the Desaguadero at the village of Calacoto (kilom. 

 316 ; alt. 12,485 feet). The latter river flows out of Lake Titicaca, 

 and drains southwards into Lake Poopoo, from which there is no 

 visible outlet. 



From Calacoto onwards the country is more or less broken up 

 by small parallel chains, rising to no great height when compared 

 with the main ' Cordilleras,' and separated one from the other by 

 wide alluvial tracts, which were originally, without a doubt, the 

 site of a great system of lakes : of these Lake Titicaca still in 

 part survives, and furnishes us with clear evidence of its former 

 magnitude. A conspicuous landmark in this district is the Alto de 

 Comanche (kilom. 364), a steep-sided mountain, which rises to a 

 considerable altitude above the level of the plateau. 



Beyond Yiacha (kilom. 416 ; alt. 12,635 feet), 1 where connexion 

 is made with the Huaqui & Antofagasta railway, the whole surface 



1 Most of the altitudes in this part of the section are somewhat lower than 

 those given by Forbes. They are taken from my personal observations with 

 an aneroid, and from a ' Guide ' to Bolivia recently issued by the Governments 

 See Bibliography, § VI, p. 49. 



