Northfield Formation (VTDSn;0)

State	Vermont
Name	Northfield Formation
Geologic age	Devonian - Silurian
Original map label	DSn
Comments	Part of Eastern Vermont Secondary unit description per VT007. The Northfield Formation in the West Dover and Jacksonville quadrangles, VT consists of gray to dark-gray, graphitic, garnet-chlorite-quartz-muscovite-pyrite schist and phyllite. Locally, unit includes 10 cm to 1 m thick vitreous, white-weathering, light-gray quartzite with abundant blue quartz grains. Lower part of unit is locally intruded by the Whitneyville facies of the North River Igneous Suite. The Northfield is of Silurian(?) and Devonian age (Ratcliffe and Armstrong, in press).
Primary rock type	slate
Secondary rock type	phyllite
Other rock types	mica schist; siltstone; limestone
Lithologic constituents	Minor Metamorphic > Schist > Mica-schist > Biotite-schistPhyllite passes into gray quartz-sericite schist containing abundant porphyroblasts of biotite and garnet in southern Vermont. Metamorphic > Metasedimentary > Metaclastic > Phyllitedark gray to black quartz-sericite slate or phyllite Metamorphic > Metasedimentary > Metaclastic > Slatedark gray to black quartz-sericite slate or phyllite; calcareous slate north of Lamoille River Incidental Sedimentary > Carbonate > Limestone (Bed)silty crystalline limestone like that of the Waits River Formation Sedimentary > Clastic > Siltstone (Bed)
Map references	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. [http://pubs.er.usgs.gov/publication/ofr20061272]
Unit references	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. Ratcliffe, N.M. and Armstrong, T.R., in press, Bedrock geologic map of the West Dover and Jacksonville quadrangles, Windham County, Vermont: U.S. Geological Survey Miscellaneous Investigations Series Map, I-__, scale 1:24,000. [http://pubs.er.usgs.gov/publication/i2552]
Geographic coverage	Caledonia - Orange - Orleans - Washington - Windham - Windsor