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Looking north to brown weathering gravel beds. Alaska. August 22, 1902.
Concentric banding and faint bedding shown in polished and etched faces of an opal concretion from the same locality as photo 14. San Luis Obispo County, California. 1931. Plate 7-C, in U.S.Geological Survey Professional paper 212. 1943.
Photomicrograph of fresh and decomposed mineralized monzonite, development of pyrite in altered monzonite, from Eldorado shaft, Boston Consolidated group. Magnetite and original biotite are absent, pyrite appears embedded in secondary quartz associated with flocculent aggregates of biotite, probably secondary. Feldspathic constituents have gone over to sercicite. Salt Lake County, Utah. 1900, plate 26-B in U.S. Geological Survey. Professional paper 38. 1905.