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 ing with it I found that by stroking the sand with my hand downward at the surface of the dune and pressing lightly upon it by just a certain amount I could make the noise every time, whether the sand was hot or cold, dry or moist. I carefully ex-

. 45―Photograph of a mingp at the foot of the huge sand dune that flanks El Bramador, or the Roaring Mountain of Toledo, near Copiapó. The camera is inclined downward at an angle of 30°. The dark slopes of the rock spur and also individual boulders appear to be reflected in a narrow sheet of water situated about an inch above the lower edge of the photograph.

perimented with this with watch in hand and found that the sand required stroking 15 times in 20 seconds to produce the effect, and there could be little variation from this period with- out the noise ceasing.

It appears that wind is not necessary to make the noise. Anything that starts the sand rolling will produce the rhyth- mic humming noise. When the wind blows it moves forward