[1][2] In Indiana and Kentucky its equitant is the Buffalo Wallow Group.
[3] In Southern Illinois oil wells are drilled into the Tar Springs formation.
[4] Also known at the Kinkaid Limestone, this unit is made up of several smaller members.
The Negli Creek Limestone of the Kinkaid formation to the west.
The type section of both the Walche Limestone Member and the Scottsburg Limestone Member are exposures in Walche's Cut, a railway cutting on the Illinois Central Railroad.
The Tar Springs consists of interbedded sandstone and shale, creating closed reservoirs within the sand.
For this reason it is the largest oil producing formation in Illinois.
It preserves fossils dating back to the Carboniferous period.