H. B. Willman and Elwood Atherton
The Birds Member of the Wilhelmi Formation (Willman, 1973, p. 13), which overlies the Schweizer Member, is named for the railroad siding at Birds, 2 miles northwest of the type section.
The type section of the Birds Member is part of the Wilhelmi Formation type section, located in a railroad cut about 5 miles southwest of Wilhelmi Airport (SE SW SE 35, 35N-9E).
The uppermost part of the member and its contact with the overlying Elwood Formation are exposed in a ravine half a mile northeast (NW NW SE 36, 35N-9E). The Birds Member consists of 10-20 feet of slightly to moderately argillaceous, slightly cherty, thin-bedded, medium-gray dolomite. It is distinguished by several thin beds of relatively pure, finely laminated, fossiliferous dolomite.
WILLMAN, H. B., 1973, Rock stratigraphy of the Silurian System in northeastern and northwestern Illinois: Illinois State Geological Survey Circular 479, 55 p.
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