Wamsutta Formation

Rhyolite and mafic volcanic rocks in the Wamsutta Formation. Wamsutta Formation occurs in Narragansett and Norfolk basins. Consists of conglomerate, lithic graywacke, sandstone, and shale. Also contains rhyolite and basalt horizons near Attleboro. Northwest of Attleboro, Wamsutta overlies Diamond Hill Felsite as used by Skehan and Murray (in Skehan and others, 1979). Volcanic rocks similar to Diamond Hill Felsite crop out west of Lake Pearl, between Franklin and Wrentham, on west flank of Norfolk basin. These are shown within Wamsutta Formation on MA State bedrock map of Zen and others (1983) because of their proximity to Diamond Hill. They also resemble Proterozoic Z Mattapan Volcanic Complex. Chute (1966) described lenses of carbonate rock in red and green shale in Wamsutta in Norwood quad. Limestone also observed in rocks mapped as Wamsutta adjacent to exposed Dedham Granite at Manchester Pond Reservoir (J.P. Schafer, 1982, oral commun.). Red and green shales may actually be Cambrian. Upper member of Pondville Conglomerate grades into and interfingers with Wamsutta; in turn, Wamsutta interfingers with Rhode Island Formation in northwest part of Narragansett basin. Nonconformably overlies Dedham Granite. Partly equivalent to Rhode Island Formation. Age is Early and Middle Pennsylvanian. Contains a few plant fossils (Goldsmith, 1991).
State Massachusetts
Name Wamsutta Formation
Geologic age Middle and Lower Pennsylvanian
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanic > RhyoliteRhyolite and mafic volcanic rocks in the Wamsutta Formation.
Igneous > Volcanic > Mafic-volcanicRhyolite and mafic volcanic rocks in the Wamsutta Formation.
Comments Part of Milford-Dedham Zone (Tertiary and Older Rocks). Secondary unit description per MA023.
References
NGMDB product
Counties Bristol - Norfolk