THE yirUATE FIELDS OF CHILE 



213 



A Rio seco, or " Dry Uiver," in a sular. 



to tins apparently limitless desolation. But almost the first day's stay 

 reveals part of the reason. The day is not unpleasant despite the heat 

 and the intensity of the sunlight, for the extreme dryness makes tem- 

 peratures of 90° or more quite comfortable, and the colors — the grays, 

 yellows, violet — playing over the sands, help make up for the lack of 

 living green. The nights are wonderful — cool, crisp, refreshing, with 

 the brilliancy of sky that only deserts can have; while the moonlight 

 gleaming from millions of salt crystals lights up the land with an effect 

 of half day and renders into attractive forms the most prosaic objects. 

 Presumably dryness also was a factor in the formation of the nitrate 

 beds. It seems certain from the kinds of rocks found there that the area 

 between the Coast Eanges and the Andes once was occupied by a bay or 

 long arm of the sea. Then the land began to rise, cutting off the bay 

 and converting it into a lagoon, entered perhaps by every high tide. 

 About its borders great flocks of birds congregated — as they do now 

 along the neighboring ocean — to feed on the prolific life in the shallow, 

 warm waters. Enormous deposits of bird guano accumulated about its 

 shores as the years went on. Meanwhile, however, the land was rising 

 higher and higher, water came into the lagoon only from the land, bring- 

 ing with it soluble nitrates from the guano. But this supply of water was 

 too small to keep up the level; and as the region became drier and drier, 

 evaporation reduced the original sea to a string of lakes occupying iso- 

 lated basins in the lower parts of the pampa. As evaporation went on, 

 these waters became too salty for life to endure. With their food supply 

 gone, the birds were forced to seek other haunts and the accumulation 

 of guano stopped. Streams and occasional rains, perhaps more frequent 

 then than now, washing away the guano, brought together in the lakes 

 compounds of nitrogen and soda, and the formation of nitrate of soda 

 was the result. Eventuallv these waters became saturated witli the differ- 



