Five mappable units have been established in an area formerly mapped as pre-Cambrian in southwestern Maine. The geologic column from oldest to youngest is as follows: the Cambrian Pejepscot quartz-feldspar-biotite gneiss and schist; the Taylor Brook gneiss; the Cambro-Ordovician Androscoggin lime-silicate gneiss, marble, and biotite schist; and the Silurian Sabattus quartz-mica-sillimanite schist and the Winthrop chloritoid phyllite. All are former sedimentary rocks.

Large igneous bodies, including granite, granodiorite, gabbro, syenite, and pegmatite, and their associated dikes, are regarded as late Paleozoic.

Correlation of the Sabattus formation with the middle Silurian Waterville shales, 50 miles northeast of Lewiston, is suggested. An attempted correlation, southeastward across the general strike from Lewiston into an area previously mapped as Carboniferous, indicates either a Paleozoic age for this area or a possible erosional interval between the early Paleozoic and the Carboniferous formations.

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