|Name||Hoosac Formation, Plymouth Member|
|Comments||Part of Green Mountains, Camels Hump Group Secondary unit description per VT012: Revised the Plymouth Member of the Hoosac Formation of Doll and others (1961) to the Plymouth Formation. Consists of a series of feldspathic and dolomitic quartzites, dolostones and black phyllites that overlie probable Middle Proterozoic gneisses. The Plymouth Formation can be divided into several informal members. The lower contact of the formation is below a sequence of dolomitic quartzites or thin bedded quartzite. Dark laminated silty phyllites laterally replace the more feldspathic quartzites and dark-gray schistose quartzites, massive vitreous quartzites, and dolomitic quartzites pass upward to the east into well bedded cream-weathered light-gray dolostone breccia; these lithologies make up the dolostone member of the Plymouth Formation. The upper member of the Plymouth Formation is a black graphitic and siliceous phyllite that contains 1 to 3 cm thick layers of dark-gray ferruginous quartzite, dolomitic quartzite, and ribbony beds of dolostone. The upper contact of the Plymouth Formation is placed at the first occurrence of light-silvery-green magnetite-muscovite-quartz knotted phyllites of the Pinney Hollow Formation. Age changed to Late Proterozoic and Early Cambrian (Ratcliffe and others, 1993) per VT004.|
|Primary rock type||quartzite|
|Secondary rock type||dolostone (dolomite)|
|Other rock types||phyllite; schist|
Metamorphic > Metasedimentary > Metaclastic > Quartzitequartzite, schistose quartzite, dolomitic quartzite
Sedimentary > Carbonate > Dolostone
Metamorphic > Metasedimentary > Metaclastic > Phyllitecarbonaceous phyllite
Metamorphic > Schistschistose quartzite, quartz-sericite-chlorite-albite schist; carbonaceous albite schist
Nicholson, S.W., Dicken, C.L., Horton, J.D., Foose, M.P., Mueller, J.A.L., and Hon, Rudi, 2006, Preliminary integrated geologic map databases for the United States: Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, Rhode Island, and Vermont: U.S. Geological Survey Open-File Report 2006-1272.
Doll, C.G., Cady, W.M., Thompson, J.B., Jr., and Billings, M.P., 1961, Centennial Geologic Map of Vermont: Vermont Geological Survey, Miscellaneous Map MISCMAP-01, scale 1:250,000.