The accompanying geochemical maps are based in part on data published in U.S. Geological Survey Professional Paper 450-E, Article 180 (Brokaw and others, 1963), and in part on new data acquired since the publication of Professional Paper 450-E. The mercury was determined by atomic absorption techniques, as described by Vaughn and McCarthy (1964), the silver by standard emission spectrographic techniques, and the tellurium, arsenic, and antimony by wet chemical methods.