|Geologic age||Late Devonian|
Sedimentary > Clastic > Mudstone > Shale > Black-shale (Bed)
Sedimentary > Carbonate > Limestone (Bed)
|Comments||Secondary unit description from USGS Geologic Names lexicon (ref. MI016): The Antrim is dark gray or brown to largely black, highly carbonaceous, thinly laminated shale with meager fossil content except for profuse algal spores. Large dark brown, bituminous and pyritic limestone concretions occur in the lower Antrim and are typically from 9.6 to 1.5 m in diameter.|
Milstein, Randall L. (compiler), 1987, Bedrock geology of southern Michigan: Geological Survey Division, Michigan Dept. of Natural Resources, scale 1:500,000.
USGS Geologic Names lexicon found at: http://ngmdb.usgs.gov/Geolex/
|Counties||Alcona - Alpena - Antrim - Benzie - Berrien - Charlevoix - Cheboygan - Emmet - Grand Traverse - Kalkaska - Leelanau - Lenawee - Macomb - Manistee - Monroe - Montmorency - Oakland - Oscoda - Otsego - Presque Isle - Saint Clair - Sanilac - Washtenaw - Wayne|