Historical:Farmington Shale 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: McLeansboro Group >>Modesto Formation >>Farmington Shale Member
Chronostratigraphy: Paleozoic Erathem >>Pennsylvanian Subsystem >>Desmoinesian Series
Allostratigraphy: Absaroka Sequence


M. E. Hopkins and J. A. Simon

Name Origin

The Farmington Shale Member of the Modesto Formation (Savage, 1927, p. 309) is named for Farmington Township, Fulton County.

Type Section

Farmington Township is the type locality (8N-4E) (Wanless, 1956, p. 11).

Extent and Thickness

The Farmington ranges from a few feet to as much as 50 feet thick in eastern, western, and southern Illinois and to as much as 100 feet or more in southeastern Illinois.

Stratigraphic Position

The Farmington is the lowest named unit of the Modesto Formation in most of the state. It generally occurs immediately above the Danville (No. 7) Coal Member, but in several places a dark gray, very impure limestone, usually less than a foot thick, lies directly on the coal. In other places black fissile shale, seldom more than 2 feet thick, overlies the coal or occurs between the limestone and the Farrnington Shale.


It is commonly gray shale that becomes coarser grained upward, and the lower part generally contains marine fossils. It has been extensively mined for clay in the Danville region, Vermilion County.


SAVAGE, T. E., 1927, Significant breaks and overlaps in the Pennsylvanian rocks of Illinois: American Journal of Science, v. 14, p. 307-316.
WANLESS, H. R., 1956, Classification of the Pennsylvanian rocks of Illinois as of 1956: Illinois State Geological Survey Circular 217, 14 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation