Cataract Formation (MISc;0)

State	Michigan
Name	Cataract Formation
Geologic age	Early Silurian
Original map label	Sc
Comments	Secondary unit description from USGS Geologic Names lexicon (ref. MI016): Named for Cataract, Ontario, CAN. Fifty feet of rocks previously assigned to Medina formation at Niagara Falls, NY, reassigned to Cataract formation. Occurs from Niagara Falls to Manitoulin Islands in Lake Huron. At Manitoulin Islands, lower 45 ft consists of thin-bedded magnesian limestone; upper 65 ft consists of red, nonfossiliferous shales. Thickness is 82 ft at Cataract, where it also fossiliferous. Age is Silurian.
Primary rock type	shale
Secondary rock type	limestone
Other rock types	dolostone (dolomite); sandstone
Lithologic constituents	Major Sedimentary > Clastic > Mudstone > Shale (Bed) Minor Sedimentary > Carbonate > Dolostone (Bed) Sedimentary > Carbonate > Limestone (Bed) Sedimentary > Clastic > Sandstone (Bed)
Map references	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
Unit references	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 (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Chippewa - Delta - Luce - Mackinac - Schoolcraft