@misc{indiciae061aea653581,
  title = {Preliminary structural map showing contours on the horizon of number 9 coal in the Henderson area, Kentucky},
  author = {E.J. Harvey},
  year = {1951},
  doi = {10.3133/ofr51114},
  url = {https://pubs.usgs.gov/publication/ofr51114},
  note = {Source identifier: ofr51114}
}