Figs. 3, 10, 16. Dement member of Grand Detour formation. Limestone, dolomitic, medium-bedded, and nonshaly. Thickness about 7 feet. Shown on columnar section as underlying Walgreen member (new) of Grand Detour formation and overlying Briton member (new) of Mifflin formation. Age is Middle Ordovician.
[Notable exposures in Dixon-Oregon area, northern IL.]
Source: US geologic names lexicon (USGS Bull. 1200, p. 1086-1087).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
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