Historical:Walgreen Member

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Handbook of Illinois Stratigraphy
Series Bulletin 95
Author H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date 1975
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Lithostratigraphy: Ottawa Limestone Megagroup >>Platteville Group >>Plattin Subgroup >>Grand Detour Formation >>Walgreen Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Blackriveran Stage
Allostratigraphy: Tippecanoe Sequence


H. B. Willman and T. C. Buschbach

Name Origin

The Walgreen Member of the Grand Detour Formation (Templeton and Willman, 1963, p. 85) is named for the Walgreen estate, on which the type section (part of the Grand Detour type section) occurs.

Type Section

The type section of the Walgreen Member is located above the Dement Member in the same type section as that of the Grand Detour (a quarry in the west bluff of the Rock River, on the Walgreen estate 2 miles north of Dixon (NE 20, 22N-9E)) where it is 8.3 feet thick.

Extent and Thickness

The Walgreen Member is generally 5-10 feet thick in the outcrop areas in northern Illinois and eastern Missouri.


Most of the Walgreen Member is gray, thin- to medium-bedded, argillaceous, shaly limestone that contains disseminated fossil debris and thin beds of purplish gray calcarenite. In the southern outcrop area it is brown, thicker bedded, and less argillaceous than in northern Illinois.


TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation