Pg. 156 (fig. 16), 170, 180-181, pl. 34. Hardwood Mountain formation. Consists of blue-gray, dark-brown-weathering, massive bedded, fine- to medium-grained, calcareous siltstone and mudstone; massive limestone conglomerate with calcareous siltstone matrix grading into massive and irregular limestone beds bearing stromatoporoid debris and tetracorals; and light-brown-weathering sandstone composed of angular quartz grains, feldspar, and small granitic pebbles. Thickness as much as 3,000 feet, top deeply eroded. No complete, well-exposed uninterrupted section known. Occurs in two large areas, one southwest of Hardwood Mountain in vicinity of Baker Pond, the other northeast of Jim Pond. Overlies basement complex, relations not directly observed. Underlies Seboomook formation and Hobbstown formation (new). Age is Late Silurian, based on presence of ostracodes DIBOLBINA, LIMBINARIA, and DIZYGOPLEURA cf. D. COSTATA (which are also found in Tonoloway limestone) and MIROCHILINA, all of which are Late Silurian. ENCRINURUS trilobite and HALYSITES chain coral preclude a Devonian age (Berdan, written commun., 1956). Report includes geologic map and correlation chart.
Type area: 1 mi southwest of Hardwood Mountain, Hobbstown Twp., Spencer [Spencer Lake] 15-min quadrangle, Somerset Co., west-central ME. Named from Hardwood Mountain [Lat. 45 deg. 26 min. 26 sec. N., Long. 70 deg. 19 min. 54 sec. W., Spencer Lake 7.5-min quadrangle].

Source: Publication; GNU records (USGS DDS-6; Reston GNULEX); US geologic names lexicon (USGS Bull. 1350, p. 320).

Mapped in Bronson Hill-Boundary Mountains anticlinorium. Includes mudstone, siltstone, calcareous slate, minor but conspicuous limestone conglomerate, and sparse limestone and medium-grained sandstone. Complex shelly fauna as well as ostracodes and trilobites were found at several localities in Spencer Lake 15-min quad. Tentatively dated in accordance with the alternative discussed by Boucot and Heath (1969) which states that the Hardwood Mountain Formation in the Spencer Lake quad is slightly older than the Silurian rocks at Fox's Camp in the Attean 15-min quad (from Albee and Boudette, 1972). Age is therefore changed from Late Silurian of Boucot (1961) to Silurian, Wenlockian and Ludlovian(?) (author uses time scale of Harland and others (1989)).

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