Light-greenish-gray, pale-greenish-yellow- or yellowish-gray-weathering, medium to fine-grained graded micaceous metasiltstone and lesser fine grained micaceous metasandstone; fine-grained beds are phyllite and micaceous metasiltstone. Graded beds are 2 to 24 cm thick. Mineralogy: quartz + muscovite + biotite + plagioclase + chlorite + magnetite + epidote. The unit contains felsic metatuff (mineral assemblage quartz + plagioclase + epidote + muscovite + biotite + chlorite + green amphibole + magnetite) and mafic metatuff (mineral assemblage blue-green amphibole + plagioclase + titanite) layers up to 180 cm thick. Maximum thickness of unit is about 2300 feet; unit overlies with apparent unconformity the Mather Gorge, Sykesville, and Yorkshire Formations, the Annandale Group, and the Piney Branch Complex (Drake and Lyttle, 1981). The unit is intruded by Occoquan Granite.
Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000.
Virginia Division of Mineral Resources, 2003, Digital Representation of the 1993 Geologic Map of Virginia, Publication 174, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, scale 1:500,000.