|Name||Plainfield Formation plus Stony Creek Granite Gneiss plus Narragansett Pier Granite|
|Geologic age||Proterozoic Z? and Permian|
Igneous > Plutonic > Granitic > GraniteStony Creek Granite Gneiss - Red to pink, unevenly medium to very coarse grained, variably foliated granite or granite gneiss, composed of oligoclase, K-feldspar, and quartz with minor biotite and magnetite, sporatic garnet (in foliated varieties), and local muscovite. Commonly contains granite and pegmatite of Narragansett Pier type (and probably age). In much of area both granites occur as innumerable veins penetrating other units or as larger bodies full of inclusions of those units, which can be mapped through the bodies of granite. Narragansett Pier Granite (Permian) - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite.
Metamorphic > Metasedimentary > Metaclastic > QuartzitePlainfield Formation - Interlayered light-gray, thin-bedded quartzite, in places with feldspar, mica, graphite, or pyrite; and diopside-bearing quartzite.
Metamorphic > GneissPlainfield Formation - light- to medium-gray gneiss composed of quartz, oligoclase, and biotite (rarely microcline); dark-grey or green gneiss composed of plagioclase, quartz, biotite, and hornblende (commonly with diopside). Stony Creek Granite Gneiss - Red to pink, unevenly medium to very coarse grained, variably foliated granite or granite gneiss, composed of oligoclase, K-feldspar, and quartz with minor biotite and magnetite, sporatic garnet (in foliated varieties), and local muscovite.
Metamorphic > SchistPlainfield Formation - medium- to dark-gray schist composed of quartz, oligoclase, biotite, sillimanite, and garnet.
Igneous > Plutonic > Granitic > Leucocratic-granitic > PegmatiteStony Creek Granite Gneiss - Commonly contains granite and pegmatite of Narragansett Pier type (and probably age). Narragansett Pier Granite - Considerable associated pegmatite.
Metamorphic > Metasedimentary > Calc-silicate-rockPlainfield Formation - calc-silicate rock
Metamorphic > AmphibolitePlainfield Formation
|Comments||Part of Eastern Uplands; Avalonian (Continental) Terrane; Avalonian Anticlinorium; Zsc only = East Haven granitic body (may be equivalent to Sterling Plutonic-Group) (includes Light House Gneiss, Branford Gneiss, and Stony Creek Granite Gneiss) (Proterozoic Z?). Printed map has individual descriptions for each unit; digital map combines all 3.|
Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.