Marcellus Shale (Hall, 1839; Butts and Edmundson, 1966). Shale, dark-gray to black, more or less fissile, pyritic. Thickness estimated to be 500 feet in Frederick County and 350 to 400 feet in the Massanutten synclinorium (Rader and Biggs, 1976). Needmore Formation (Willard, 1939). Shale, dark or greenish gray, with thin beds or nodules of black, argillaceous limestone and the Tioga metabentonite beds (Dennison and Textoris, 1970), generally present with the Millboro or Marcellus Shale and is disconformable with the underlying Ridgeley Sand tone. Thickness ranges from 0 to 160 feet and is replaced to the southwest by the Huntersville Chert.