Cataract Formation

Cataract Formation
State Michigan
Name Cataract Formation
Geologic age Early Silurian
Lithologic constituents
Sedimentary > Clastic > Mudstone > Shale (Bed)
Sedimentary > Carbonate > Limestone (Bed)
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Carbonate > Dolostone (Bed)
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.

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:

NGMDB product
Counties Chippewa - Delta - Luce - Mackinac - Schoolcraft