Historical:Farmington Shale Member
M. E. Hopkins and J. A. Simon
The Farmington Shale Member of the Modesto Formation (Savage, 1927, p. 309) is named for Farmington Township, Fulton County.
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.
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.
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