Type locality and use of name in Indiana: The name Hardinsburg, generally credited to Brokaw (1916 1917, p. 23; pl. 1), was presented by him as "tentative and subject to revision." The first description was offered by Butts (1917, p. 96) under the name Hardinsburg Sandstone. This unit in its type locality is 30 feet (10 m) thick and contains, in descending order, shaly sandstone, massive cliff-forming sandstone, and thin-bedded fine-grained well-indurated sandstone. The formation was named for Hardinsburg, Breckinridge County, Ky.
The name Hardinsburg Sandstone was first used in Indiana by Malott and Thompson (1920, p. 522). Later the name was modified to Hardinsburg Formation in recognition of the large quantity of shale in the unit (Gray and others, 1957, p. 6; pl. 3).
Description: In Indiana the Hardinsburg Formation is characteristically gray soft carbonaceous shale and very fine grained ripple-bedded sandstone that is cliff forming in some places. Thickness of the unit, which is recognized in surface exposures from central Greene County to the Ohio River, ranges from 20 to 62 feet (6 to 19 m) (Gray and others, 1957, pl. 2; Gray, Jenkins, and Weidman, 1960, p. 39). In the subsurface it is thicker and contains more sandstone. The Hardinsburg overlies the Haney Limestone conformably in most places, but a disconformably relationship, such as that noted in Illinois by Potter (1963, p. 58, fig. 42A), has also been observed in the subsurface in Knox and Gibson Counties, Ind. (Kline, 1952). The Hardinsburg is overlain conformably by the Glen Dean Limestone or disconformably by the Mansfield Formation (Morrowan).
Correlation: The Hardinsburg Formation is recognized throughout the Illinois Basin and is a part of the standard Chesterian section (Swann, 1963; Willman and others, 1975, p. 157-158). On the basis of a comprehensive paleontologic study, the Visean-Namurian boundary of European usage has been placed within the Hardinsburg Formation (Horowitz and others, 1979, p. 206).