Lithotectonic assemblages as portrayed on the new bedrock geologic map of Massachusetts.

Scale of 1:250,000. The map units are grouped into eight lithotectonic packages. Five "zones" of older rocks that cover the whole state are, from west to east, the Taconic-Berkshire, Rowe-Hawley, Bronson Hill, Nashoba, and Milford-Dedham. In central and western Massachusetts, these zones are overlain by the Connecticut Valley and Merrimack "belts" of Silurian-Devonian, and local Carboniferous, strata; the two belts are distinguished from each other on the basis of the lithofacies of the Silurian strata. In eastern Massachusetts, the Milford-Dedham Zone also includes Silurian-Devonian, Carboniferous, Mesozoic, and Tertiary strata. A Mesozoic "basin" is separately identified in the Connecticut Valley region