104 PROCEEDINGS OF THE NATIONAL MU8EVM. vol.54. 



The western Andes consist chiefly of Mesozoic deposits, together 

 with innmnerable lava flows and ash beds of the great series of high 

 volcanoes, whose greatest activity appears to have been reached in 

 very late geologic times. The Cordillera Occidental, with many 

 peaks between 19,000 and 21,000 feet in altitude, forms the western 

 ramparts of the high Bolivean plateau or ''altaplanicie," which ex- 

 tends from the Vilcanota massif of Peru southward to the Argentine 

 frontier — a distance of about 500 miles and with an average width 

 of about 80 miles. It has an average elevation of between 12,000 and 

 13,000 feet, and is bleak and inhospitable in the north (the "puna")j 

 and arid and barren toward the south — the desert of Lipez— with saline 

 depressions, and ridges and peaks rising through the flat mantle of 

 Pleistocene and Recent deposits. 



The eastern ramparts of the " altaplanicie " are formed by the 

 somewhat fanned-out chains of the eastern Andes or "CordiUera 

 Real," consisting largely of folded Paleozoics with granitic cores and 

 other igneous intrusives, in part at least of late Tertiary age, forming 

 a series of high peaks, a number of which reach above 21,000 feet. 

 It is about 250 miles from the western range of the Cordillera Real 

 to the Sierra de Cochabamba and the Sierra de Misiones, which form 

 the eastern boundary of this imposhig mountain mass. It is in the 

 midst of this extremely rugged montane countr;/ that Potosi rises 

 to a height of 15,381 feet, surrounded on all sides by much higher 

 peaks. 



Three-fifths of the area of Bolivia lies east of the CordiUera Real, 

 and forms a part of the Amazon and Paraguay drainage basins. 

 The latter region consists of gently imdulating forests, low alluvial 

 grass-covered plains (llanos), great swamps, and flooded bottom 

 lands. 



Little can be said of the details of either the existing climate or 

 vegetation of much of Bolivia. The lowlands east of the mountains, 

 comprising the Provinces of El Beni, Santa Cruz, Chuquisaca, and 

 Tarija, together with the eastern mountain valleys below 5,000 feet, 

 are termed "yungas" (a climatic term) and have a humid tropical 

 climate. The higher valleys of the eastern Andes between 5,000 and 

 9,500 feet, where they are situated so as to receive the moisture- 

 laden northeast trade winds, have a subtropical character. Above 

 9,500 feet and up to 11,000 feet the climate is in general temperate 

 and suitable for raising vegetables and cereals. Between 11,000 feet 

 and 12,500 feet in the mountains, and consequently including the 

 high plateau, is the "puna" or region of cold and aridity, with two 

 seasons — a cold summer or autumn and a winter. The air is cold 

 and dry and the growing season is too short for anything except oca 

 (Oxalis) quinoa (Chenopodium) , potato, barley, and coarse grasses. 



