@misc{indiciae807764c9bf3a,
  title = {Coal resources of Butler County, Pennsylvania},
  author = {Elmer Davisson Patterson and Junius Adrian. Van Lieu},
  year = {1969},
  doi = {10.3133/ofr69193},
  url = {https://pubs.usgs.gov/publication/ofr69193},
  note = {Source identifier: ofr69193}
}