@misc{indiciae70b8d2cf14cf,
  title = {Geology and mineral resources of the Butler and Zelienople quadrangles, Pennsylvania},
  author = {George Burr Richardson},
  year = {1936},
  doi = {10.3133/b873},
  url = {https://pubs.usgs.gov/publication/b873},
  note = {Source identifier: b873}
}