The Seelyville, De Koven, and Davis Coal Members (Spoon and Staunton Formations, Illinois and Indiana) or beds (Carbondale Formation, western Kentucky) presently are considered stratigraphically separate seams of restricted regional extent in the basin. Recent subsurface investigation reveals that the De Koven and Davis Coals are splits of the Seelyville Coal. A 170-mi-long (275-km) cross section, with an average of one well per mile, links the type Seelyville of west-central Indiana with the type Davis (Western Kentucky No. 6) and De Koven (Western Kentucky No. 7) Coals of western Kentucky. Geophysical logs formed the basis of the correlations. In its type area, the Seelyville Coal contains several partings of shale, one of which is fairly continuous but variable in thic ness, ranging from less than 1 in. (2.5 cm) to more than 20 ft (6 m). Southward, this parting continues as a clastic wedge (more than 100 ft, 30 m, thick in some places) that separates the De Koven Coal (above) from the Davis Coal (below) in their area of outcrop in southeastern Illinois.

Knowledge that these coals are equivalent rather than separate seams should increase understanding of previously mapped resources, and facilitate mapping of additional resources in the future.

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