@misc{indiciaeb0db98d9da08,
  title = {Coal beds of the Troublesome quadrangle, Breathitt, Knott, and Perry Counties, Kentucky},
  author = {Allen D. Williamson and W.L. Adkison},
  year = {1953},
  doi = {10.3133/coal18},
  url = {https://pubs.usgs.gov/publication/coal18},
  note = {Source identifier: coal18}
}