|Name||Tatnic Hill Formation|
|Geologic age||Ordovician or Proterozoic Z|
Metamorphic > Schistsulfidic sillimanite schist, sillimanite schist
Metamorphic > Gneisssillimanite schist and gneiss, biotite gneiss; minor calc-silicate gneiss
Metamorphic > Amphibolite
Metamorphic > Metasedimentary > Calc-silicate-rock
Metamorphic > Metasedimentary > Metacarbonate > Marble
|Comments||Part of Nashoba Zone (Silurian and Older Rocks). The age of the Putnam Group, including its Tatnic Hill Formation, is considered to be Late Proterozoic(?) based on the 730 my age of the Fishbrook Gneiss in MA and the 440 my age of the Hedgehog Hill gneiss intruded into the upper part of the younger Brimfield Group (Pease, 1989) per MA009.|
Zen, E-An (ed.), Goldsmith, R. (comp.), Ratcliffe, N.M. (comp.), Robinson, P. (comp.), Stanley, R.S. (comp.), Hatch, N.L., Jr., Shride, A.F., Weed, E.G.A., and Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000.
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.