Historical:Schweizer 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: Hunton Limestone Megagroup >>Wilhelmi Formation >>Schweizer Member
Chronostratigraphy: Paleozoic Erathem >>Silurian System >>Alexandrian Series
Allostratigraphy: Tippecanoe Sequence


H. B. Willman and Elwood Atherton

Name Origin

The Schweizer Member of the Wilhelmi Formation (Willman, 1973, p. 13), the basal member, is named for Schweizer School a mile east of the type section.

Type Section

The type section of the Schweizer 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).

Extent and Thickness

Although widely present in subsurface in northeastern Illinois and as much as 80 feet thick, the Schweizer Member is well exposed only in and near the type section, where it is 25 feet thick.


The Schweizer Member consists of medium to dark gray dolomitic shale at the base that grades to very argillaceous, silty dolomite at the top. A thin bed of limestone conglomerate marks the base in the type section.


WILLMAN, H. B., 1973, Rock stratigraphy of the Silurian System in northeastern and northwestern Illinois: Illinois State Geological Survey Circular 479, 55 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation