Usage:
Forreston Member of Grand Detour Formation of Platteville Group (IL)
Geologic age:
Late Ordovician (Mohawkian; Turinian)
Type section, locality, area and/or origin of name:
Type section: quarry on north side of ravine, 1 mi northwest of Brookville, in NE/4 SE/4 NW/4 sec. 21, T. 24 N., R. 7 E., [approx. Lat. 42 deg. 03 min. 50 sec. N., Long. 89 deg. 41 min. 48 sec. W., Brookville 7.5-min quadrangle], Carroll Co., northwestern IL (Templeton and Willman, 1963, Illinois Geol. Survey Bull., no. 89, p. 87; Willman and Buschbach, 1975, Illinois Geol. Survey Bull., no. 95, p. 47-87).
Named from Forreston, [Forreston 15-min quadrangle], Ogle Co., northern IL, 7 mi northeast of type section (Templeton and Willman, 1963, p. 87; Willman and Buschbach, 1975).
Notable exposures in Dixon-Oregon area, northern IL (Templeton and Willman, 1952).
AAPG geologic province:
Wisconsin arch
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"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 conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).