Usage:
No current usage.
(†Middlebrook Group (MO-recognized locally in St. Francois Mountains area) considered abandoned.)
Subunits:
Royal Gorge Rhyolite, Pilot Knob Felsite, Oak Mountain Rhyolite, Marlow Mountain Rhyolite, Clark Mountain Rhyolite, Stegall Rhyolite, and miscellaneous unnamed units.
Geologic age:
Precambrian
Type section, locality, area and/or origin of name:
Not designated. Named from exposures near town of Middlebrook, Iron Co., MO (Tolman and Robertson, 1969).
AAPG geologic province:
Midcontinent region
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 ([ ]).