Walloomsac Formation (MAOwm;0)

State	Massachusetts
Name	Walloomsac Formation
Geologic age	Middle Ordovician
Original map label	Owm
Comments	Part of Taconic-Berkshire Zone (Ordovician and Older Rocks) Thin limestone unit near base of Walloomsac locally contains abundant bryozoan fragments, cup corals, pelmatozoan hash, and conodonts that indicate that the base of the Walloomsac is Rocklandian (middle and late Caradocian) or younger. Age of unit is Middle Ordovician per MA011.
Primary rock type	marble
Secondary rock type	phyllite
Other rock types
Lithologic constituents	Major Metamorphic > Metasedimentary > Metaclastic > Phylliteinterbedded black phyllite Metamorphic > Metasedimentary > Metacarbonate > Marblegraphite-albite-biotite calcitic marble and schistose marble
Map references	Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.
Unit references	Zen, E-An (ed.), Goldsmith, R. (comp.), Ratcliffe, N.M. (comp.), Robinson, P. (comp.), Stanley, R.S. (comp.), Hatch, N.L., Jr., Shride, A.F., Weed, E.G.A., Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000. Ratcliffe, N.M., Potter, D.B. and Stanley, R.S., 1993, Bedrock geologic map of the Williamstown and North Adams quadrangles, Massachusetts and Vermont, and part of the Cheshire quadrangle, Massachusetts: U.S. Geological Survey Miscellaneous Investigations Series Map, I-2369, 13 p., 2 sheets, scale 1:24,000. [http://pubs.er.usgs.gov/publication/i2369]
Geographic coverage	Berkshire