@misc{indiciae4cd0b7aae862,
  title = {Digital assessment of northern and central Appalachian basin coals},
  author = {L.F. Ruppert and S.J. Tewalt and L. J. Bragg and R.N. Wallack},
  year = {1999},
  url = {https://pubs.usgs.gov/publication/70021220},
  note = {Source identifier: 70021220}
}