Narragansett Bay Group - Wamsutta Formation

Red sandstone, shale, and conglomerate, locally containing abundant volcanic detritus as clasts and matrix. Plant fossil localities occur in adjacent Massachusetts. Minor, but significant amounts of interstratified bimodal-composition volcanic lava flows consisting of alkalic basalt (locally pillowed) and rhyolite are present in adjacent Massachusetts.
State Rhode Island
Name Narragansett Bay Group - Wamsutta Formation
Geologic age Pennsylvanian
Lithologic constituents
Sedimentary > Clastic > Sandstone
Sedimentary > Clastic > Mudstone > Shale
Sedimentary > Clastic > Conglomerate
Comments Part of Esmond-Dedham Subterrane. Narragansett Bay Group - deposited upon older rocks of both West Bay and East Bay parts of the Esmond-Dedham subterrane. Secondary unit description from USGS Geologic Names lexicon (ref. RI013): Wamsutta described as interbedded red, coarse-grained conglomerate, some felsite, lithic graywacke, sandstone, and shale. Contains a few lenses of limestone and one flow of red rhyolite and several sheets of altered mafic volcanics. Thickness is 595 m.

Hermes, O.D. (comp.), Gromet, L.P. (comp.), Murray, D.P. (comp.), Hamidzada, N.A., Skehan, J.W., and Mosher, S., 1994, Bedrock geologic map of Rhode Island: Rhode Island Map Series No. 1, Kingston, Rhode Island, scale 1:100,000.

USGS Geologic Names lexicon found at:

NGMDB product
Counties Providence