"Aerial photographs of the nitrate region of Tarapaca, Chile, reveal features of the topographic setting of the deposits which bear significantly on the problem of their origin. Nitrate accumulations prevail on the lower slopes of the old-age Coast range bordering the west side of an alluvium-filled depression between that range and the Andes but the deposits seem to rise too high up the slopes to have been derived from the waters of the alluvial flats. Analysis of various theories of origin points to a derivation by weathering and concentration from the predominating lavas and tuffs of the bed rock."

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