The chief stratigraphic perplexities of the Floyds Knob and Edwards‐ville formations of the Borden (Knobstone) group in Indiana result from the presence of several large, disconnected and irregularly distributed masses of calcareous rock inclosed in clastic strata. These masses, which are dominantly crinoidal limestone, are fittingly designated by the term “bioherm” which has been proposed by Cumings and Shrock.2 Like buried coral reefs, they have caused unnecessary confusion because of inadequate understanding of their nature and stratigraphic associations. The writer’s attention was drawn to these structures during a study of the stratigraphy of the entire Borden group of southern Indiana.3
A brief summary of the major features of the Borden stratigraphy is here presented. The Borden group of Indiana comprises the lower Mississippian rocks between the Rockford (Kinderhook) limestone beneath and the Harrodsburg (Warsaw) limestone above. Prior . . .