e 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. In general, the sub-tropical (_valle_)
and temperate (_cabezera de valle_) regions of Bolivia are healthy and
agreeable, have a plentiful rainfall, moderate temperature in the
shade, and varied and abundant products. There is a high rate of
mortality among the natives, due to unsanitary habits and diet, and
not to the climate. In the tropical _yungas_ the ground is covered
with decaying vegetation, and malaria and fevers are common. There are
localities in the open country and on exposed elevations where healthy
conditions prevail, but the greater part of this region is considered
unhealthy. The prevailing winds are easterly, bringing moisture across
Brazil from the Atlantic, but eastern Bolivia is also exposed to hot,
oppressive winds from the north, and to violent cold winds (_surazos_)
from the Argentine plains, which have been known to cause a fall of
temperature of 36 deg. within a few hours. According to the _Sinopsis
Estadistica y Geografica de la Republica de Bolivia_ (La Paz, 1903),
the average mean temperature and the an