@misc{indiciae1e8404c7de04,
  title = {Geologic map of the Balkan quadrangle, Bell and Harlan Counties, Kentucky},
  author = {A.J. Froelich and James Tazelaar},
  year = {1973},
  doi = {10.3133/gq1127},
  url = {https://pubs.usgs.gov/publication/gq1127},
  note = {Source identifier: gq1127}
}