| State | Connecticut |
|---|---|
| Name | Gneiss (metavolcanic) member [of Brimfield Schist] |
| Geologic age | Upper? and Middle Ordovician |
| Lithologic constituents |
Major
Metamorphic > SchistMedium-gray, medium-grained, layered gneiss and schist, composed of oligoclase, quartz, and biotite; some gneiss and most schist layers contain garnet and sillimanite.
Metamorphic > GneissMedium-gray, medium-grained, layered gneiss and schist, composed of oligoclase, quartz, and biotite; some gneiss and most schist layers contain garnet and sillimanite; some gneiss layers contain garnet, hornblende or pyroxene or grade into amphibolite or calc-silicate rock.
Incidental
Metamorphic > Amphibolite
Metamorphic > Metaigneous > MetavolcanicProbably includes metavolcanic rocks.
Metamorphic > Metasedimentary > Calc-silicate-rock
|
| Comments | Part of Eastern Uplands; Iapetus (Oceanic) Terrane - Merrimack Synclinorium; Brimfield Schist and equivalent formations (includes Tatnic Hill Formation) (Upper? and Middle Ordovician). The age of the Brimfield Group in this area is Cambrian(?) based on the intrusion of 440 my Hedgehog Hill gneiss in the top of the Hamilton Reservoir Formation in the upper part of the Brimfield, although the top of the Brimfield may be Ordovician or older Paleozoic (Pease, 1989) per CT013. |
| References | Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.Pease, M.H., Jr., 1989, Correlation of the Oakdale Formation and Paxton Group of central Massachusetts with strata in northeastern Connecticut: U.S. Geological Survey Bulletin, 1796, 26 p.https://pubs.er.usgs.gov/publication/b1796 |
| NGMDB product | |
| Counties | Middlesex - Tolland - Windham |