@misc{indiciaeeccd85ba83fe,
  title = {Correlation chart of Pennsylvanian rocks in Alabama, Tennessee, Kentucky, Virginia, West Virginia, Ohio, Maryland, and Pennsylvania showing approximate position of coal beds, coal zones, and key stratigraphic units},
  author = {Leslie F. Ruppert and Michael H. Trippi and Ernie R. Slucher},
  year = {2014},
  doi = {10.3133/pp1708d.2},
  url = {https://pubs.usgs.gov/publication/pp1708D.2},
  note = {Source identifier: pp1708D.2}
}