@misc{indiciae2f142d7c66b5,
  title = {Geology and mineral resources of part of the Cumberland Gap coal field, Kentucky},
  author = {G. H. Ashley and L. C. Glenn},
  year = {1906},
  doi = {10.3133/pp49},
  url = {https://pubs.usgs.gov/publication/pp49},
  note = {Source identifier: pp49}
}