Mt. Greylock
       7 ½’ quadrangle: Williamstown, MA
       Berkshire County
       Mt. Greylock State Reservation
       Appalachian Trail
       Berkshire Mountains

Metamorphic (metamorphosed sedimentary)
3,491 ft (1,064 m)

Bedrock: Greylock schist

Lower Cambrian to Late Proterozoic

Light green, lustrous quartz-muscovite-chloritoid phyllite, dark gray white-spotted quartz-albite-biotite schist, with minor beds of quartzite, conglomerate and pink dolomite marble. These rocks lie in thrust contact above the Ordovician schists, quartzites and marbles of the autochthonous Walloomsac Formation. The thrust sheet carried continental slope sediments westward onto the continental shelf during the Middle Ordovician Taconian Orogeny. Similar in origin to the highpoints of Connecticut and Vermont.

Surficial Geology: The Wisconsinan ice sheet overtopped the summit, attested to by southeast-trending glacial grooves. Memorial Tower at the summit is made of Quincy Granite, a greenish riebeckite granite from Quincy, Massachusetts.

Soil Series: Tunbridge/Lyman complex: Lyman: steep, extremely stony dark brown shallow soil, the Tunbridge similar but less steep. Both formed in acid glacial till derived from mica schist.

Selected References:

  • Ratcliffe, Nicholas M., D.B. Potter and R.S. Stanley, 1993, Bedrock geologic map of the Williamstown and North Adams quadrangles, Massachusetts and Vermont, and part of the Cheshire quadrangle, Massachusetts: U.S. Geological Survey Miscellaneous Investigations Series Map I-2369.
  • Scanu, Richard J., 1988, Soil Survey of Berkshire County, Massachusetts : U.S. Soil Conservation Service.
  • Skehan, James W., S.J., 2001, Roadside Geology of Massachusetts : Mountain Press Publishing Company, Missoula, Montana, p.287, 318-319.

Other suggested sources of information:

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