Figs. 3, 9, 15C. Hazel Green member of Quimbys Mill formation. Consists of massive whitish-weathering dolomite about 1 to 3 feet thick. Shown on columnar section as basal member of Quimbys Mill formation. Underlies Shullsburg member (new); overlies Everett member (new) of Nachusa formation (new). Age is Middle Ordovician.
[Notable exposures in Dixon-Oregon area, northern IL.]

Source: US geologic names lexicon (USGS Bull. 1200, p. 1714).

Pg. 233-234; T.L. Thompson, 1991, Missouri Dept. of Nat. Res., Div. Geol. and Land Survey Rept. of Inv., no. 70, pt. 2, p. 168. The Hazel Green Member of Quimbys Mill Formation of Plattin subgroup [informal] of Platteville Group of Templeton and Willman (1963) and Willman and Kolata (1978) not recognized in Missouri. Quimbys Mill Formation = upper part of Macy Limestone of Plattin Group in Missouri.
The Quimbys Mill Formation was proposed for Platteville strata of the Illinois basin, and was extended into Missouri by Templeton and Willman (1963). However, the nomenclature proposed in 1951 by Larson was found by Thompson (1991) to more adequately represent Plattin strata in Missouri, and Quimbys Mill was not used. Age is Ordovician (Mohawkian).
References cited:
Larson, E.R., 1951, "Stratigraphy of the Plattin group, southeastern Missouri," AAPG Bull., v. 35, p. 2041-2075.
Templeton, J.S., and Willman, H.B., 1963, "Champlainian Series (Middle Ordovician) in Illinois," Illinois Geol. Survey Bull., no. 89, 260 p.
Willman, H.B., and Kolata, D.R., 1978, "The Platteville and Galena Groups in northern Illinois," Illinois State Geol. Survey Circ., no. 502, 75 p.
["Subgroup" not recognized as a formal stratigraphic rank term (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). Considered informal and should not be capitalized.]

Source: Publication.