State | Connecticut |
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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 |