|Name||Plainfield Formation plus Potter Hill Granite Gneiss plus Narragansett Pier Granite|
|Geologic age||Proterozoic Z? and Permian|
Metamorphic > Metasedimentary > Metaclastic > QuartzitePlainfield Formation - Interlayered light-gray, thin-bedded quartzite, in places with feldspar, mica, graphite, or pyrite; diopsite-bearing quartzite.
Igneous > Plutonic > Granitic > GraniteNarragansett Pier Granite - 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 > GneissPlainfield Formation - light- to medium-gray gneiss composed of quartz, oligoclase, and biotite (rarely microcline), dark-gray or green gneiss composed of plagioclase, quartz, biotite, and hornblende (commonly with diopside). Potter Hill Granite Gneiss - Light-pink to gray, tan-weathering, fine- to medium-grained, rarely porphyritic, well-foliated (not lineated) granitic gneiss, composed of microcline, quartz, oligoclase (or albite), biotite, and magnetite, minor muscovite, and local garnet.
Metamorphic > SchistPlainfield Formation - medium- to dark-gray schist composed of quartz, oligoclase, biotite, sillimanite, and garnet.
Igneous > Plutonic > Granitic > Leucocratic-granitic > PegmatiteNarragansett Pier Granite - Considerable associated pegmatite.
Metamorphic > AmphibolitePlainfield Formation
Metamorphic > Metasedimentary > Calc-silicate-rockPlainfield Formation - calc-silicate rock
|Comments||Part of Eastern Uplands; Avalonian (Continental) Terrane. Units are described seperately on printed map; combined in digital map.|
Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.