Eminence Dolomite - dolomite with some druse - coated chert. Potosi Dolomite - dolomite with abundance of druse - coated chert.
Chiefly alkali rhyolitic ash - flow tuffs, lava flows, and bedded tuffs, with minor trachytes.
Derby-Doerun Dolomite - alternating thin dolomite, siltstone, and shale; Davis Formation - glauconitic shale with fine - grained sandstone, limestone, and dolomite); Bonneterre Dolomite - dolomite, dolomitic limestone, and limestone; glauconitic in lower part.
St. Francois Mountains intrusive suite (subvolcanic, alkali granitic ring complexes).
Sandstone with some dolomitic and shaly lenses; coarse - graines to conglomeratic and arkosic at base.
Coarse - crystalline cherty dolomite with a basal Gunter Sandstone Member.
Diabase dikes and sills.