Early work by numerous investigators (Robinson 1963, Tracy et al. 1976, Robinson et al. 1982, 1986a, b) provides a structural and metamorphic framework for the Acadian metamorphic high in central Massachusetts within which changes in phase composition and assemblage in the rocks can be correlated. Six metamorphic zones have been distinguished (Tracy et al. 1976, Robinson et al. 1982), reflecting prograde (T) metamorphic conditions in graphite-bearing pelitic rocks (Fig. 1) that range from the amphibolite through to the lower granulite facies. The T and P estimates are based mainly on A. B. Thompson’s (1976) pioneering work in quantifying T and P using biotite-garnet Fe/Mg exchange and the garnet-cordierite-sillimanite-quartz assemblage, respectively.