Walloomsac Formation

Dark-gray, graphitic quartz phyllite and schist containing minor lenses of limestone.
State Massachusetts
Name Walloomsac Formation
Geologic age Middle Ordovician
Lithologic constituents
Major
Metamorphic > Schistgraphitic quartz phyllite and schist
Metamorphic > Metasedimentary > Metaclastic > Phyllitegraphitic quartz phyllite and schist
Minor
Sedimentary > Carbonate > Limestone (Lens)
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 - Hampden