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 valley of Copiapé, the fog hangs over the hills and the bay a good part of the time. In the sketch, Figure 19, the belt of fog is shown surmounting the coastal hills and reaching inland over the valley. [It does not sweep up the valley, as it does in the small draws of the Coast Range that slope directly down to the Pacific, but settles down from aloft as night comes on, and in the morning the whole valley may be filled with it. Tt is indeed a strange experience to be in the midst of desert country, so far removed from the sea that there is neither sight nor sound of it, and yet awake in the morning to find the air filled with a clammy, cold fog. It does not long survive the morning sun, and after a few hours of daylight the edge of it may be seen retreating up the slopes to the crests of the coastal hills.

Riding northward through the coastal desert toward the Huasco valley Darwin in 1835 observed the belt of fog from elevated points along the trail and wrote; ‘During the winter months, both in northern Chile and in Peru, a uniform bank of clouds hangs, at no great height, over the Pacific. From the mountains we had a very striking view of this white and brilliant aerial-ficld, which sent arms up the valleys, leaving islands and promontories in the same manner, as the sea does in the Chonos archipelago and in Tierra del Fuego."

As for distribution through the year there may be said to be a cloudy season and a cloudless season. The cloudless sea- son comes in the southern summer from November to April, and the cloudy season in the southern winter from May to October. So far as the coast has rain directly or indirectly from the fog bank that hangs over its margin, it is a winter rain, more characteristic of subtropical than tropical lands. For the characteristic summer rains of the tropics one must cross the foggy coastal belt, continue across the coastal desert and enter the cordillera, where regular summer rains prevail at elevations that vary from 4000 to 10,000 feet according to the latitude. Over the whole Central Andes it is the rule that the southern summer (December to February) is the season of rain, the winter the season of comparative dryness.