@misc{indiciae4b039b8e8de2,
  title = {Map showing generalized thickness contours of the Pittsburgh coal bed in Pennsylvania, Ohio, West Virginia, and Maryland},
  author = {S. J. Tewalt and L.F. Ruppert and L. J. Bragg and Richard Carlton and David Brezinski and R.N. Wallack},
  year = {1997},
  doi = {10.3133/ofr97748},
  url = {https://pubs.usgs.gov/publication/ofr97748},
  note = {Source identifier: ofr97748}
}