National Geologic Map Database

Geologic Unit: Glencoe


Glencoe Member of Spechts Ferry Formation (IL,IA,MN,MO,WI)
Glencoe Shale Member of Spechts Ferry Formation of Decorah Group (IL*,MO*)


Millbrig Bentonite Bed (IL,WI).

Geologic age:

Late Ordovician (Mohawkian)*

Type section, locality, area and/or origin of name:

Type section: exposure in south bluff of Meramec River along St. Louis-San Francisco RR, 0.25 mi northeast of Mincke Siding, near center E/2 SE/4 SE/4 sec. 21, T. 44 N., R. 4 E., Manchester 7.5-min quadrangle, St. Louis Co., eastern MO. Named from village of Glencoe, St. Louis Co., eastern MO, 3 mi west of type section (Templeton and Willman, 1963).
Reference sections in MO: (1) roadcut on U.S. Interstate Highway I-55, mileage 182, in NW/4 SW/4 NW/4 sec. 6, T. 41 N., R. 6 E., Herculaneum 7.5-min quadrangle, Jefferson Co.; (2) roadcut on north frontage road of U.S. Interstate Highway I-44, west of Allenton-Six Flags exit, in sec. 33, T. 44 N., R. 3 E., western St. Louis Co.; (3) exposure on St. Louis County Road W., 1 mi south of Eureka, in NW/4 NW/4 NE/4 sec. 12, T. 43 N., R. 3 E., Pacific 7.5-min quadrangle, St. Louis Co.; and (4) roadcut on U.S. Highway 61 north of bridge over Spencer Creek, in SE/4 SE/4 sec. 21, T. 55 N., R. 4 W., Ralls Co. (Thompson, 1991).

AAPG geologic province:

Illinois basin*
Iowa shelf
Ozark uplift*
Wisconsin arch

For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).