Middle member [of Bigelow Brook Formation] (CTSObm;0)

State	Connecticut
Name	Middle member [of Bigelow Brook Formation]
Geologic age	Silurian or perhaps Ordovician
Original map label	SObm
Comments	Part of Eastern Uplands; Iapetus (Oceanic) Terrane - Merrimack Synclinorium; Hebron Gneiss and equivalent formations (including equivalents of Paxton and Oakdale Formations of Massachusetts) (including Bigelow Brook and Southbridge Formations) (Silurian and Ordovician). The age of the Brimfield Group and its Bigelow Brook, Hamilton Reservoir, and Mount Pisgah Formations in this area is considered to be Cambrian(?) based on the intrusion of 440 m.y. Hedgehog Hill gneiss emplaced near the top of the Hamilton Reservoir Formation in the upper part of the Brimfield, although the top of the Brimfield, at least, may be Ordovician or older Paleozoic (Pease, 1989) per CT013.
Primary rock type	calc-silicate rock
Secondary rock type	schist
Other rock types	granofels
Lithologic constituents	Major Metamorphic > Metasedimentary > Calc-silicate-rockGreenish-gray, medium-grained calc-silicate rock, composed of plagioclase, quartz, and diopside (locally hornblende and scapolite). Minor Metamorphic > Schistinterbedded with schist and granofels composed of plagioclase, quartz, biotite, and commonly garnet and sillimanite Metamorphic > Granoblastic > Granofelsinterbedded with schist and granofels composed of plagioclase, quartz, biotite, and commonly garnet and sillimanite
Map references	Connecticut Geological and Natural History Survey, DEP, in cooperation with the U.S. Geological Survey, 2000, Bedrock Geology of Connecticut, data format: shapefile, file name: bedrock, downloaded from: http://magic.lib.uconn.edu/cgi-bin/MAGIC_DBsearch2.pl?Geography=37800&Loc=0000 on 9/18/2003, scale 1:50,000. [http://magic.lib.uconn.edu/connecticut_data.html#environmental] [http://magic.lib.uconn.edu/cgi-bin/MAGIC_DBsearch2.pl?Geography=37800&Loc=0000]
Unit references	Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 125,000. Pease, M.H., Jr., 1989, Correlation of the Oakdale Formation and Paxton Group of central Massachusetts with strata in northeastern Connecticut: U.S. Geological Survey Bulletin, 1796, 26 p. [http://pubs.er.usgs.gov/publication/b1796]
Geographic coverage	Tolland - Windham