THE BOLIVIAN LAKES. 363 



basin variously known as Pampa-Aullagas, Poopo, Oruro, from the towns on or 

 near its banks. Into this land-locked lake tlie Desaguadero discharges a volume 

 estimated at over 3,500 cubic feet per second. 



Pampa-Aullagas, which is of a more regular oval form than Titicaca, appears 

 to be niucb shallower; its survey, which, however, is far from complete, has 

 nowhere revealed depths of more than 70 feet. Panza, an island in the middle of 

 the basin, is disposed in the same direction as the general axis of the plateau. 

 Besides the Desaguadero, the lake receives a few affluents from the Eastern Cor- 

 dilleras. But the evaporation from a surface of about 1,100 square miles would 

 appear to exceed the contributions from all these sources, for the effluent escaping 

 south-westwards has apparently a mean discharge of scarcely 35 cubic feet per 

 second. 



This outlet even disappears for some distance in the sands, reappearing lower 

 down under the Aymara name of Laca Ahuira, "Effluent," which is soon lost in 

 the saline Coipasa marshes. Other rivulets also descend from the Western Cordillera 

 towards this shallow depression, which is transformed to a temporaiy lake during 

 tbe wet season. The Coipasa morass, standing at an altitude of 11,000 feet above 

 the sea, occupies almost the lowest part of the Titicaca hydrographie depression. 

 If, however, the surveys can be trusted, it would still be some 10 feet higher than 

 another Bolivian basin, the extensive saline swamp of Empeza, which lies farther 

 south, to the west of the Huanchaca mines. Owing to the argillaceous mud of 

 their bed these marshy tracts are completely impassable during the rainy season ; 

 but in summer they offer a solid surface over 3 feet thick, formed by thin 

 alternate layers of salt and clay. 



The Beni and Madre de Digs. 



At present the La Paz gorge, through which the inland sea formerly sent its 

 overflow to the Amazons, gives rise only to the La Paz torrent, so named from the 

 city on its banks. But before escaping from the mountains this rivulet is joined 

 by larger streams, such as the Cotocayes, and the Altamachi, forming with them 

 the Rio Beni, which winds away north and north-east to the Madeira affluent of 

 the Amazons. Although comparable in volume to the most copious rivers of 

 Europe, the majestic Rio Beni is, nevertheless, surpassed by the Mamore, which 

 rises, under the name of the Rio Grande, in the Bolivian Andes between the Cor- 

 dillera Real and the Cochubamba ranges. After describino: a vast semicircular 

 bend round the north-eastern ramparts, the Mamore is swollen by numerous 

 affluents descending from the northern slope of the mountains, the southern waters 

 of which it had alread}^ collected. 



The Beni is also rivalled by the Madre de Dios, which has its source in Peru, 

 but in its middle and lower course flows through Bolivian territory. According 

 to the missionary Armentia, who navigated both rivers, the Madre de Dios is the 

 larger of the two, thanks to its copious main branch, the Rio Inambari. Pent up 

 in a rocky longitudinal valley at the foot of the Carabaya highlands, it receives 



