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 of the denudation of the land. The Copiapé region is marked by the latter type of desert valley and basin: i. ©. the streams collect the run-off over a great extent of territory and by con- verging it in one main valley subject the people now to great floods and again to long periods of extreme low water accord- ing as there are floods and droughts in the head-water region. Were a still greater desert drainage to be gathered together the extremes of water level would be still greater, although there is at least one corresponding advantage—there is some water in all years. Salt incrustations are not infrequent in the Copiapé valley, but they are only a few inches thick at most. Where water stagnates and evaporates a salt deposit gathers, and this renders irrigation the more difficult in certain places. Thus we have here near the border of the westerlies a type of drainage distinct from (1) that in the still drier north where the mountain streams terminate on the land, and (2) that in the wetter south, where the streams always reach the sea.

The people of Copiapé and Vallenar are accustomed to see- ing black clouds in the sky and no rain, a white blanket of snow in the cordillera and none upon the nearer hills, heavy fogs and some rain upon the coast and occasional fogs and only a few light showers a year in the valley. They take these things as a matter of course, but to one who is studying such an environ- ment in the field or to the newcomer who thinks of what all that distant water would do if turned out upon the irrigable land in the valley, it seems an extraordinary handicap. But it is not where rain falls, it is where it can be put to best use, that determines the site of a desert settlement. Our own connec- tion with rain upon the cornfields and wheatfields of the Mid- dle West is direct and immediate. A shower in one township benefits that township and not a neighboring one. In the des- ert the situation is quite different. Pastures spring up in regions of rain and snow, as in the cordillera and in the coastal hills; but for agriculture there is required irrigation, and this takes not merely water but also flat land upon which water can be diverted from irrigating canals.