Description: ÒProduction of phosphate, pyrite, and sulphur in North America in 1913É Each dot represents 1 per cent of worldÕs production. A cross represents less than 1/2 per cent of worldÕs production. — Department of the Interior, 1921 Source: Department of the Interior , World Atlas of Commercial Geology (Washington, DC: Department of the Interior , 1921) Plate 50 Map Credit: Courtesy the private collection of Roy Winkelman
