Silurian lithology and correlation in southern Illinois and Indiana are discussed, with particular reference to the Bainbridge limestone and related beds.

The Bainbridge formation of southeastern Missouri represents the Niagaran sediments of this area. The average thickness of the formation along the outcrop in Missouri is about 130 feet. Eastward in the subsurface of Illinois thicknesses of 200 feet or more are found.

The Niagaran of southeastern Indiana includes the Louisville, Waldron, Laurel, and Osgood formations. These formations total about 80 feet in thickness at the outcrop and thicken to more than 200 feet in southwestern Indiana.

Lithologic and electric-log characteristics are discussed, along with criteria for subsurface identification.

Cross-section studies trace the Silurian beds from their outcrop in Missouri through the subsurface of Illinois and Indiana to the outcrop along the Cincinnati arch. Correlations are based essentially on lithologic and stratigraphic relationships.

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