Oak Grove member of the Carbondale formation. Name applied to 20+/- feet of undescribed beds of alternating limestones and shale in lower part of Carbondale formation of central western Illinois. Said to underlie Purington shale and overlie his [H.R. Wanless'] Francis Creek shale, which rests on coal No. 2. Age is considered Pennsylvanian.
Origin of name not stated.
Source: US geologic names lexicon (USGS Bull. 896, p. 1524).
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 ([ ]).