|Geologic age||Late Ordovician|
Sedimentary > Clastic > Mudstone > Shale > Black-shale (Bed)
Sedimentary > Carbonate > Limestone (Bed)
|Comments||Secondary unit description from USGS Geologic Names lexicon (ref. MI016): Named the Collingwood formation for Collingwood, Ontario, CAN. Unit is a thin formation of layers of fine-grained rather pure blue limestone alternating with thick beds of soft brown shale. Thickness is not known but appears to be less than 50 feet. Fauna, which is well developed at Collingwood, differs from that of typical Utica in many respects. Overlies Trenton limestone and underlies darker shales containing typical Utica fauna. The Collingwood is of Ordovician age.|
Reed, Robert C., and Daniels, Jennifer (compilers), 1987, Bedrock geology of northern 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||Alger - Chippewa - Delta - Luce - Schoolcraft|