Skip to main content

Walloomsac Formation

Walloomsac Formation - Blue-gray and white mottled crystalline limestone lenses near base of the Walloomsac locally yielding fragments of pelmatozoa, bryozoa and cup coral.
State Massachusetts
Name Walloomsac Formation
Geologic age Middle Ordovician
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 limestone
Secondary rock type
Other rock types
Lithologic constituents
Major
Sedimentary > Carbonate > Limestone (Lense)Blue-gray and white mottled crystalline limestone lenses near base of the Walloomsac locally yielding fragments of pelmatozoa, bryozoa and cup coral.
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Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.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.