Preston Gabbro plus Quinebaug Formation

Preston Gabbro - Dark, medium- to coarse-grained, mainly massive gabbro, composed of labradorite, augite, and opaques, generally with hornblende, locally hypersthene, or olivine or both. Quinebaug Formation - Medium- to dark-gray, commonly greenish, medium-grained, well-layered gneiss, composed of hornblende, andesine, biotite, and epidote, commonly with quartz or garnet, interlayered with amphibolite.
State Connecticut
Name Preston Gabbro plus Quinebaug Formation
Geologic age Middle Ordovician or older
Lithologic constituents
Major
Metamorphic > GneissMedium- to dark-gray, commonly greenish, medium-grained, well-layered gneiss, composed of hornblende, andesine, biotite, and epidote, commonly with quartz or garnet.
Igneous > Plutonic > Gabbroic > GabbroPreston Gabbro - Dark, medium- to coarse-grained, mainly massive gabbro, composed of labradorite, augite, and opaques, generally with hornblende, locally hypersthene, or olivine or both.
Minor
Metamorphic > AmphiboliteQuinebaug Formation - interlayered with amphibolite.
Comments Part of Eastern Uplands; Iapetus (Oceanic) Terrane - Merrimack Synclinorium; Units are described seperately on printed map; combined in digital map.
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 New London