Roxbury Conglomerate of Proterozoic Z to earliest Paleozoic age used. Consists of Brookline, Dorchester, and Squantum Members, but they are not separately mapped.

Source: GNU records (USGS DDS-6; Reston GNULEX).

Authors state, "...historic stratigraphy and stratigraphic units of the Boston basin are suspect." They suggest that the only formal nomenclature that should be retained is Boston Bay Group, undifferentiated, and perhaps the Weymouth Formation and the Braintree Argillite. Units within the Boston Bay Group--the Cambridge Argillite, and the Brookline, Dorchester, and Squantum (Tillite) Members of the Roxbury Conglomerate--were defined largely on the basis of the percentage of conglomerate, diamictite, argillite, sandstone, siltstone, tuff, and matrix present. Authors believe that recognition of these units in the field is nearly impossible and propose a facies-derived model for the Boston basin. They suggest that the Boston Bay Group was deposited in a submarine fan/slope/apron environment.

Source: GNU records (USGS DDS-6; Reston GNULEX).

Dorchester Member of Roxbury Conglomerate consists of interbedded argillite and sandstone forming an intermediate unit between primarily conglomeratic Brookline Member and overlying Cambridge Argillite. Age is Proterozoic Z and possibly Early Cambrian. Report contains geologic map and correlation charts. [Chapters A-J in U.S. Geological Survey Professional Paper 1366 are intended as explanations and (or) revisions to 1:250,000-scale MA State bedrock geologic map of Zen and others (1983).]

Source: GNU records (USGS DDS-6; Reston GNULEX).