Redefined as slate, phyllite, and metasiltstone coinciding approximately with Emerson's (1889, 1899) belt of Worcester Phyllite. Extends from Worcester area northward into towns of Clinton and Shirley, excluding fossiliferous strata and related rocks of Pennsylvanian age mapped by Grew (1970 and other reports); excludes mica schist facies, Vaughn Hills Member, phyllite facies, and Harvard Conglomerate Lentil. Former members are raised in rank to Vaughn Hills Quartzite and Harvard Conglomerate. Equivalent to units 3 and 4 of Peck (1976) and to eastern belt of Holden Formation of Grew (1970). As redefined, the formation north of Worcester lies east of western belt of the Oakdale Quartzite of Emerson (1917; Peck's unit 5) and west of the eastern belt of Emerson's Oakdale Quartzite (unit 2 of Peck). Offset by Pine Hill fault at Worcester and cut off by faults to the north near MA-NH border. In Worcester area, Worcester Formation is in apparent conformable contact with Oakdale Quartzite of Emerson (as mapped by Peck, 1976, and Grew, 1970), which is considered to be probable Silurian. Worcester is intruded by granite of Fitchburg Complex (name revised) which has an Early Devonian age (R.E. Zartman and R.S. Naylor, written commun., 1978). Worcester is compositionally and structurally similar to Early Devonian Shapleigh Group of Hussey (1968) in southern ME. Hussey correlated Shapleigh with Early Devonian Littleton Formation in its type area in NH. Robinson (1981) observed graded bedding that indicates that Worcester underlies Oakdale. Because Worcester is in stratigraphic sequence with probable Silurian rocks and is intruded by Early Devonian Fitchburg Complex, age of Worcester is most likely Silurian to Early Devonian. However, the stratigraphic sequence that includes the Worcester may be older than Silurian and Devonian if radiometric ages from Ayer Granite and Newburyport Complex are correct (discussed in this report). Worcester is shown in its structural and possible stratigraphic position above the Oakdale rather than in a possible stratigraphic position beneath the Oakdale. On the basis of above evidence, Worcester is assigned a Silurian and probably Early Devonian age.

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

Used as Worcester Formation of Silurian and Early Devonian age.

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