@misc{indiciaefaec0546df1f,
  title = {The lower Pennsylvanian unconformity in the central Appalachian Basin},
  author = {R. E. Thomas and K. J. Englund},
  year = {1999},
  doi = {10.3133/i2597},
  url = {https://pubs.usgs.gov/publication/i2597},
  note = {Source identifier: i2597}
}