Type locality and use of name: The name Dugger Formation was used by Wier (1950 1952, p. 17) in describing rocks exposed in secs. 31 and 32, T. 8 N., R. 7 W., and secs. 5 and 6, T. 7 N., R. 7 W., 2 miles (3.2 km) northeast of Dugger, Sullivan County, Ind. These descriptions placed the lower boundary of the formation at the top of the Alum Cave Limestone Member later, however, this boundary was lowered to include the Alum Cave and the underlying black shale (Wier, 1961, 1965; Wier and Gray, 1961). As now recognized, the Dugger Formation extends from the top of the Springfield Coal Member of the Petersburg Formation to the top of the Danville Coal Member.
Description: The Dugger Formation, the uppermost formation in the Carbondale Group, includes in ascending order the Bucktown, Herrin, Hymera, and Danville Coal Members; the Alum Cave, Antioch, Providence, and Universal Limestone Members; the Anvil Rock and Bridge Junction Sandstone Members; and unnamed beds of clay, sandstone, and shale. The Dugger Formation is underlain by the Petersburg Formation of the Carbondale Group and overlain by the Shelburn Formation of the McLeansboro Group. The basal unit of the formation is commonly an unnamed black fissile shale that contains fish remains and concretions of ironstone and limestone as much as 3 feet (0.9 m) in diameter (Wier, 1961, 1965). In places a thin pyritic limestone underlies the black shale (Wier, 1952, p. 15).
The Dugger Formation ranges from 73 to 185 feet (22 to 56 m) in thickness and averages 130 feet (40 m) (Wier, 1965). It crops out from the Ohio River in Warrick County to Vermillion County in westernmost central Indiana.
Correlation: The Dugger is correlative with the upper part of the Carbondale Formation of Illinois and the upper part of the Carbondale Formation and the lower part of the Sturgis Formation of Kentucky.