The Silurian strata considered in this paper crop out in the bluffs and adjacent uplands of the lower Mississippi River drainage basin. Striking lithology characterizes a part of the Niagaran section in the area. It includes chiefly the argillaceous composition and the reddish color of the rocks. The argillaceous nature of the beds is incorporated in shaly limestones, not in preponderant shales. The red color is modified by greenish gray mottling on the bedding surfaces and by aggregates of that color within the rock. The red shales, clays, and argillaceous limestones of the Dixon formation of west Tennessee are typical of the variegated Niagaran beds elsewhere in the region. Dixon lithology, alone, does not support ultimate correlations, everywhere, however.

This paper deals with possible Niagaran correlations between west Tennessee, southwest Illinois, and southeast Missouri, with some attention devoted to the Niagaran in northeast Arkansas and in the Arbuckle Mountains. The suggested correlations rest chiefly on lithology and stratigraphic relations. The known fossil evidence, with possibly one exception, is not in striking contradiction to the criteria used. Summer field work has been in progress since 1938. A stratigraphic table embodying some of the possible applications of the study in analysis of Silurian rocks in southwest Illinois and southeast Missouri is submitted.