Walloomsac Formation

Orange-brown weathering, graphite-albite-biotite calcitic marble and schistose marble and interbedded black phyllite.
State Massachusetts
Name Walloomsac Formation
Geologic age Middle Ordovician
Lithologic constituents
Major
Metamorphic > Metasedimentary > Metaclastic > Phylliteinterbedded black phyllite
Metamorphic > Metasedimentary > Metacarbonate > Marblegraphite-albite-biotite calcitic marble and schistose marble
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.
References
NGMDB product
Counties Berkshire