Pg. 262. Adamstown Granite. Porphyritic adamellite. Is a deformed and metamorphosed pluton. Age is Late Ordovician.
Type section: Lat. 45 deg. N., Long. 70 deg. 50 min. to 70 deg. 55 min. W., north-central part of Oquossoc quadrangle, Oxford Co., west-central ME.

Source: US geologic names lexicon (USGS Bull. 1520, p. 6).

Adamstown Granite here assigned to the Highlandcroft Plutonic Suite (revised). Six of Highlandcroft's eight plutons were dated by U-Th-Pb methods. Age ranges from 453 to 443 Ma. Individual ages are (from north to south): Attean Quartz Monzonite, 443+/-4 Ma; Adamstown Granite, about 453 Ma; Highlandcroft Granodiorite, 450+/-5 Ma; these three dates support Naylor's (1969) conclusion that the Highlandcroft and Oliverian Plutonic Suites are coeval. The East Inlet pluton, located 20 km northwest of the Highlandcroft belt, yields a younger age of 430+/-4 Ma. Zircons from the Fairlee Quartz Monzonite and Lost Nation pluton (a quartz monzonite) yield scattered isotopic data. Fairlee is about 450 Ma and Lost Nation is about 440 Ma. Geologically, the Fairlee may be coeval with the East Inlet. On the basis of these ages, geologic constraints, and time scale consideration, the age of the Highlandcroft Plutonic Suite magmatism ranges from Middle or Late Ordovician throughout at least the Early to Middle Silurian.

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