Southbridge Formation

Dark- to light-gray, locally rusty, fine- to medium-grained interlayered granofels and schist, composed of quartz, plagioclase, and biotite, with muscovite in schist, and amphibole, calc-silicate minerals, K-feldspar in certain layers; also locally mappable units and thinner layers of calc-silicate rock, amphibolite, and sillimanite-garnet and sillimanite-graphite-pyrrhotite schist.
State Connecticut
Name Southbridge Formation
Geologic age Silurian or Ordovician or both
Lithologic constituents
Major
Metamorphic > Granoblastic > GranofelsDark- to light-gray, locally rusty, fine- to medium-grained interlayered granofels and schist, composed of quartz, plagioclase, and biotite, with muscovite in schist, and amphibole, calc-silicate minerals, K-feldspar in certain layers.
Metamorphic > SchistDark- to light-gray, locally rusty, fine- to medium-grained interlayered granofels and schist, composed of quartz, plagioclase, and biotite, with muscovite in schist, and amphibole, calc-silicate minerals, K-feldspar in certain layers; and sillimanite-garnet and sillimanite-graphite-pyrrhotite schist.
Minor
Metamorphic > Metasedimentary > Calc-silicate-rockthinner layers of calc-silicate rock
Metamorphic > Amphibolite
Comments Part of Eastern Uplands; Iapetus (Oceanic) Terrane - Merrimack Synclinorium; Hebron Gneiss and equivalent formations (including equivalents of Paxton and Oakdale Formations of Massachusetts) (including Bigelow Brook and Southbridge Formations) (Silurian and Ordovician). Same as SOs
References

Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.

NGMDB product
Counties Tolland