Field investigations started in 1925 by the writer led to a growing interest in the confusing stratigraphic problems of the lower half of the Mississippian system in the east-central interior of the United States, especially in Indiana, Kentucky, Ohio, and to a lesser extent in Tennessee. Studies were first undertaken in southern Indiana where the major part of four summers was spent in the field; this led to the preparation of a detailed report entitled The Borden (Knobstone) Rocks of Southern Indiana, published in 1931. This study disclosed numerous problems directed toward the adjoining areas and thus gave impulse to the investigation of additional territory. Soon, therefore, the problems of lower Mississippian rocks were viewed in the light of broader, regional relationships. Necessity was seen for an expansion of detailed field studies in order to clarify issues arising from the study of literature. Stratigraphic correlations were especially perplexing and badly confused. With the aid of a field assistant in the spring of 1934, 14 weeks were spent surveying the lower Mississippian outcrop belt which surrounds the Lexington Plain in Kentucky. This resulted in linking the Indiana studies with those of Ohio. Much less extensive field studies have been made in parts of northern and eastern Tennessee and parts of Ohio, during short portions of the summers of 1930 and 1936.
The principal objectives in the preparation of this paper are: (1) To give, in a single report, a summary of the essential elements in the stratigraphy of the entire lower . . .