Talladega Group; Lay Dam Formation

Interbedded dark-green phyllite, medium-gray to light-brown and black metasiltstone, dark-green feldspathic metagraywacke, and light-gray and dark-gray medium to coarse-grained arkosic quartzite and metaconglomerate; graphitic phyllite common in upper part. In Cleburne and Calhoun Counties, rocks mapped as the Lay Dam include the Abel Gap Formation of Bearce (1973) and consist of interbedded greenish-gray metasiltstone and quartzite, black phyllitic metasiltstone, medium-gray to greenish-gray arkosic quartzite, and dark-gray pyritic quartzite. In Clay Chounty the upper part of the Lay Dam includes black graphitic sericite phyllite and slate reportedly containing plant fossils (Erin Slate Member).
State Alabama
Name Talladega Group; Lay Dam Formation
Geologic age Silurian?-Devonian
Lithologic constituents
Major
Metamorphic > Metasedimentary > Metaclastic > PhylliteLay Dam Formation - interbedded dark-green phyllite, graphitic phyllite common in upper part; In Cleburne and Calhoun Counties, rocks mapped as the Lay Dam include the Abel Gap Formation of Bearce (1973) and consist of black phyllitic metasiltstone; In Clay county the upper part of the Lay Dam includes black graphitic sericite phyllite
Metamorphic > Metasedimentary > Metaclasticmedium-gray to light-brown and black metasiltstone, dark-green feldspathic metagraywacke, metaconglomerate; In Cleburne and Calhoun Counties, rocks mapped as the Lay Dam include the Abel Gap Formation of Bearce (1973) and consist of interbedded greenish-gray metasiltstone and quartzite, black phyllitic metasiltstone.
Minor
Metamorphic > Metasedimentary > Metaclastic > QuartziteLay Dam Formation - light-gray and dark-gray medium to coarse-grained arkosic quartzite; In Cleburne and Calhoun Counties, rocks mapped as the Lay Dam include the Abel Gap Formation of Bearce (1973) and consist of interbedded greenish-gray metasiltstone and quartzite, medium-gray to greenish-gray arkosic quartzite, and dark-gray pyritic quartzite.
Incidental
Metamorphic > Metasedimentary > Metaclastic > SlateIn Clay county the upper part of the Lay Dam includes slate reportedly containing plant fossils (Erin Slate Member).
Comments Printed map has units 'tld' and 'tldd' in one description, split them up here. Secondary unit description from USGS Geologic Names lexicon (ref. AL002: Lay Dam Formation of Talladega Group consists of polymictic greenish-gray thick and irregularly bedded metaclastics (graywacke, siltstone, sandstone, and arkose). May include thin zones of chlorite schist, graphite slate and bluish-gray to grayish-orange silty limestone. Contains quartzite beds and a conglomeratic facies of bouldery metagraywacke with clasts up to 3 ft in diameter in Coosa and Chilton Cos. In Cleburne and Calhoun Cos, the Lay Dam includes rocks previously assigned to the Abel Gap Formation of Bearce (1973), which consist of interbedded greenish-gray metasiltstone and quartzite, black phyllitic metasiltstone, medium-gray to greenish-gray arkosic quartzite, and dark-gray pyritic quartzite. Includes three members: the Miller Mill Quartzite Member, the Erin Slate Member and the Cheaha Quartzite Member. A significant regional angular unconformity is present at the base of the Lay Dam. Age is Silurian(?) to Devonian(?).
References

Szabo, M.W., Osborne, E.W., Copeland, C.W. Jr., and Neathery, T.L., 1988, Geologic Map of Alabama, Geological Survey of Alabama Special Map 220, scale 1:250,000.

USGS Geologic Names lexicon found at: http://ngmdb.usgs.gov/Geolex/

https://ngmdb.usgs.gov/Geolex/search

NGMDB product
Counties Bibb - Calhoun - Chilton - Clay - Cleburne - Coosa - Talladega