H. B. Willman and T. C. Buschbach
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.
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.
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