Historically, much of the lower Pennsylvanian of Indiana has been considered to be generally nonmarine in origin. The presence of coals, the abundance of plant fossils, the lack of marine fossils, and the influential reports published by Potter and Siever during the 1950s and 1960s regarding sandstone deposition helped set the image of lower Pennsylvanian deposition as predominately fluvial with only minor marine influence. Recent work in Indiana, however, has revealed that many mudstone- dominated intervals were deposited under a tidal influence. In some cases, these marine-influenced intervals overlie coals that have sulfur contents of less than 1 percent.