|Name||Preston Gabbro plus Quinebaug Formation|
|Geologic age||Middle Ordovician or older|
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.
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.|
Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.