_Climate._--Bolivia lies wholly within the torrid zone, and variations in temperature are therefore due to elevation, mountain barriers and prevailing winds. The country possesses every gradation of temperature, from that of the tropical lowlands to the Arctic cold of the snow-capped peaks directly above. This vertical arrangement of climatic zones is modified to some extent (less than in Argentina) by varying rainfall conditions, which are governed by the high mountain ranges crossing one corner of the republic, and also by the prevailing winds. The trade winds give to S. Bolivia a wet and dry season similar to that of N. Argentina. Farther north, and east of the Cordillera Oriental, rains fall throughout the year, though the summer months (November-March) are usually described as the rainy season. On the west side of the Cordillera, which extracts the moisture from the prevailing easterly winds, the elevated plateaus have a limited rainfall in the north, which diminishes toward the south until the surface becomes absolutely barren. Brief and furious rain-storms sometimes sweep the northern plateau, but these are not frequent and occur during a short season only. Electrical wind storms are frequent in these high altitudes. Bolivia has a wide range of temperature between places of the same latitude. The natives designate the Bolivian climatic zones as _yungas, valle_ or _medio yungas, cabezera de valle, puna_ and _puna brava_. The _yungas_ comprises all the lowlands and the mountain valleys up to an elevation of 5000 ft. The temperature is tropical, winter is unknown and the atmosphere is exceedingly humid. The mean temperature, according to official estimates, is 70 deg. F., but this probably represents the average between the higher elevations and the low country. The _valle_ zone includes the deep valleys from 5000 to 9500 ft., has a warm climate with moderate variations in temperature and no cold weather, is sub-tropical in character and productions, and is sometimes described as a region of perpetual summer. The _cabezera de valle_, as the name indicates, includes the heads of the deep valleys above the _valle_ zone, with elevations ranging from 9500 to 11,000 ft.; its climate is temperate, is divided into regular seasons, and is favourable to the production of cereals and vegetables. The _puna_, which lies between 11,000 and 12,500 ft., includes the great central plateau of Bolivia. It has but two seasons, a cold summer or autumn and winter. The air is cold and dry, and the warmer season is too short for the production of anything but potatoes and barley. The mean temperature is officially estimated as 54 deg. F. The _puna brava_ extends from 12,500 ft. up to the snow limit (about 17,500 ft.), and covers a bleak, inhospitable territory, inhabited only by shepherds and miners. Above this is the region of eternal snow, an Arctic zone within the tropics.