O. Feldspathic mica-schist, Chowchilla River. See 17th Ann., Part I, p. 691. Contains quartz, feldspar, biotite, muscovite, apatite, and specular iron. Analysis by W. F. Hillebrand, record No. 1461. P. R. C. 744. P. Andalusite-hornfels, Yaqui Gulch. Principally quartz, andalusite, brown and white mica, black graphite-like grafns, a little iron ore, and probably feldspar. Analysis by George Steiger, record No. 1643. Described by Turner in Bull. 150, p. 342. P. R. C. 135. Q. Andalusite-schist, Chowchilla River. See 17th Ann., Part I, p. 691. Contains quartz, biotite, andalusite, sericite, a little muscovite, probably graphite, iron ore, a few garnets, and apparently chlorite. Analysis by Hillebrand, No. 1461. P. R. C. 743. R. Chiastolite-schist, Yaqui Gulch. Contains chiastolite, sillimanite, brown mica, sericite (?), probably graphite, and clear grains which appear to be quartz and feldspar. Analysis by Steiger, No. 1643. Described by Turner in Bull. 150, p. 342. P. R. C. 135. S. Hornfels, Agua Fria Creek. See 17th Ann., Part I, p. 691. Contains quartz, brown mica, iron ore, and plagioclase. Analysis by Hillebrand, No. 1461. P. R. C. 747. 13. THE QUICKSILVER REGION. Rocks described by Becker in Mon. XIII. Analyses made by W. H. Melville in the San Francisco laboratory. With one exception (the serpentine from New Idria) all the rocks are from the districts north of San Francisco. A. Pseudo-diabase, near Mount St. Helena. Contains augite, hornblende, oligoclase, albite, zoisite, ilmenite, leucoxene, and a little chlorite. B. Pseudo-diabase, Sulphur Bank. Contains oligoclase, a little quartz, pyroxene, hornblende, ilmenite, sphene, serpentine, and chlorite. C. Pseudo-diorite, Knoxville. Mainly actinolite, with a little white mica, chlorite, serpentine, sphene, rutile, and zircon. D. Glaucophane-schist, Sulphur Bank. Mainly glaucophane and zoisite. Quartz, albite, muscovite, and sphene are also present. E. Andesitic obsidian, Clear Lake. Shows grains of plagioclase, augite, and hypersthene. Sp. gr. 2.391. F. Andesite (asperite), Clear Lake. Contains pyroxene, plagioclase, magnetite, and sometimes biotite. Pyroxene mostly rhombic. Sp. gr. 2.664. G. Obsidian, south of Borax Lake. H. Basalt, south of Burns Valley. groundmass of plagioclase and augite. I. Ordinary basalt, Knoxville. Sp. gr. 2.390. Rich in olivine, with a microlitic J. Light-green, marmolitic serpentine, New Idria. K. Black serpentine, Sulphur Bank. L. Light-green serpentine, Sulphur Bank. 14. MOUNT DIABLO. Described by Turner and Melville in Bull. Geol. Soc. Amer., vol. 2, pp. 383-414. Analyses by W. H. Melville. Those with record numbers were made in the Washington laboratory; the others were made in the laboratory at San Francisco. A. Diabase, Mitchell Canyon. Composed of augite, plagioclase, and ilmenite, with uralite and chlorite secondary. B. The same rock, partly altered and partly uralitic. Called "diabase-diorite" by Turner. C. Pyroxenite, near Bagley Creek. Composed of bronzite and diallage. Equivalent to the websterite of North Carolina. P. R. C., 735. D. Glaucophane-schist, Pine Canyon. Contains numerous cinnamon garnets. A, B, and C have the record No. 1247. E. Crystalline gabbro, Bagley Creek. Contains plagioclase and diallage. Record No. 1166. F. Shaly gabbro. Friable, containing carbonates and sulphates. Somewhat resembles serpentine. G. Shaly gabbro, like F, much resembling a true serpentine. According to Turner, F and G are merely weathered layers of the gabbro. |
