Hortonville, or Cumberland Head, and Glens Falls Formations, Undifferentiated (VTOhg;0)

State	Vermont
Name	Hortonville, or Cumberland Head, and Glens Falls Formations, Undifferentiated
Geologic age	Ordovician
Original map label	Ohg
Comments	Part of Champlain and Vermont Valleys, Trenton Group Secondary unit description from USGS Geologic Names lexicon (ref. VT030): Revised the Hortonville to the Hortonville formation of the Trenton group in the Champlain and Vermont Valleys. Consists of black, carbonaceous and pyritic slate and phyllite, locally sandy. Brown weathered limy beds are common near base. Occurs east of Highgate Springs, Champlain, and Orwell thrusts. Maximum thickness of the Hortonville in the Castleton area is at least 1000 feet. Named the Glens Falls limestone of the Trenton group for Glens Falls, Warren Co., eastern NY. Consists of thin layers of very fossiliferous limestone with shale intercalations near top and a 2 inch conglomerate layer at base. Contains ripple marks and other signs of shallow water conditions. Basal unit of Trenton group. Thickness is 17 feet. Overlies the Tribes Hill limestone or the Amsterdam limestone and underlies the Canajoharie shale. Fossils indicate that the Glens Falls is of Middle Ordovician age.
Primary rock type	slate
Secondary rock type	phyllite
Other rock types	limestone; shale; conglomerate
Lithologic constituents	Major Metamorphic > Metasedimentary > Metaclastic > Phyllite (Bed)Hortonville Formation Metamorphic > Metasedimentary > Metaclastic > Slate (Bed)Hortonville Formation Incidental Sedimentary > Clastic > Conglomerate (Bed)Glens Falls Formation Sedimentary > Clastic > Mudstone > Shale (Bed)Cumberland Head, and Glens Falls Formations Sedimentary > Carbonate > Limestone (Bed)Cumberland Head, and Glens Falls Formations
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. USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Addison - Bennington - Chittenden - Franklin - Rutland