32 THE TROPICAL WORLD. 



The dangers of these solitudes are increased by the great 

 mobility of the soil. Wlien a strong wind blows, huge sand- 

 columns, rising like water-spouts to a height of eighty or a 

 hundred feet, advance whirling through the desert, and suddenly 

 encompass the traveller, who can only save himself by a rapid 

 flight. Such is the instability of the soil, that in a few hours 

 a plain will be covered with hillocks or Medanos, and recover 

 after a few days its former level. The most experienced mule- 

 teers are thus constantly deceived in their knowledge of the road, 

 and are the first to give way to despair, while seeking to extricate 

 themselves from a labyrinth of newly-formed medanos. These 

 constant transformations and shiftings in the desert, which 

 Tschudi graphically calls ' a life in death,' take place more 

 particularly in the hot season, when the least pressure of tlie 

 atmosphere suffices to disturb the dried-up sands, whose weight 

 increases during the winter by the absorption of moisture. The 

 single grains then unite to larger masses, and more easily 

 withstand the pressure of the wind. 



The summer, or dry season, begins in November. The rays 

 of the vertical sun strike upon the light-coloured sands, and are 

 reflected with suffocating power. No plant except the cactuses 

 and tillandsias, which manage to thrive where nothing else exists, 

 takes root in the glowing soil ; no animal finds food on the life- 

 less plain ; no bird, no insect, hovers or buzzes in the stifling 

 atmosphere. Only in the highest regions the condor, the monarch 

 of the air, is seen sailing along in lonely majesty. 



In May, which in these southern latitudes corresponds to our 

 October, the scene changes. A thin, misty veil extends over 

 the sea and the coast, and, increasing in density during the 

 following months, only begins to diminish in October. At the 

 beginning and the end of this damp season the mist generally 

 ascends between nine and ten in the morning, and falls again at 

 about three in the afternoon ; but in August and September, 

 when it is most dense, it rests for weeks immovably over the 

 earth, never dissolving in rain, but merely descending in a fine, 

 penetrating drizzle, called ' garua ' by the inhabitants. In many 

 parts rain has not been known to fall for centuries, except only 

 after very severe earthquakes, and even then the phenomenon is 

 not of constant occurrence. The mist seldom ascends to a vertical 

 height of more than 1,200 feet, when it is replaced by violent 



