Hoppin Formation (MACAh;0)

State	Massachusetts
Name	Hoppin Formation
Geologic age	Middle and Lower Cambrian
Original map label	Eh
Comments	Part of Milford-Dedham Zone (Tertiary and Older Rocks) Secondary unit description per MA023 as found in USGS Geologic Names lexicon (ref. MA024): Hoppin Formation consists of green and red slaty shale, locally containing calcareous nodules, and lenses of red argillaceous limestone; arkosic quartzite (locally conglomeratic) and sandstone occur at base of formation. Nonconformity at base of formation over Dedham Granite is clearly exposed at Hoppin Hill; Early Pennsylvanian Pondville Conglomerate lies with angular unconformity above. Maximum thickness is approx 244 m. Age is Early and Middle Cambrian (Goldsmith, 1991).
Primary rock type	argillite
Secondary rock type	quartzite
Other rock types	limestone
Lithologic constituents	Major Metamorphic > Metasedimentary > Metaclastic > Argillite Minor Sedimentary > Carbonate > Limestone Metamorphic > Metasedimentary > Metaclastic > Quartzite
Map references	Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.
Unit references	Zen, E-An (ed.), Goldsmith, R. (comp.), Ratcliffe, N.M. (comp.), Robinson, P. (comp.), Stanley, R.S. (comp.), Hatch, N.L., Jr., Shride, A.F., Weed, E.G.A., Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000. Goldsmith, Richard, 1991, Stratigraphy of the Milford-Dedham zone, eastern Massachusetts; an Avalonian terrane, Chapter E, IN Hatch, N.L., Jr., ed., The bedrock geology of Massachusetts: U.S. Geological Survey Professional Paper, 1366-E-J, p. E1-E62. [http://pubs.er.usgs.gov/publication/pp1366EJ] USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Bristol - Norfolk