Page:Popular Science Monthly Volume 83.djvu/217

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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 temperatures 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 Ranges 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, bringing 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 isolated 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. Eventually these waters became saturated with the different