Re-examination of the Cynthiana Formation in Kentucky has been undertaken to relate the various named members stratigraphically and geographically. As a part of this work, a detailed study of insoluble residues from a horizon of this formation, a sequence of alternating shales and limestone, was undertaken to test the feasibility of correlation. High lateral variability of all aspects of both heavy and light fractions and overlap of zones within the vertical range of the insolubles make detailed correlations impossible. Correlation can only be made when a new heavy mineral suite or a new species appears. Size, good sorting, maturity and limited heavy mineral content of the rock indicate deposition in a shallow sea quite distant from the source area, a metamorphosed terrane of fairly high rank. Zircon, calcium garnet, amphiboles, and pyroxenes are the principal species found in the heavy fraction. Abraded and fragmental zircons are found to have a wide range of sizes whereas euhedral zircons are restricted to the silt sizes and are believed to have a bentonitic origin.

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