@misc{indiciae66906980f5c0,
  title = {Isopach Map and Regional Correlations of the Fire Clay Tonstein, Central Appalachian Basin},
  author = {William F. Outerbridge},
  year = {2003},
  doi = {10.3133/ofr03351},
  url = {https://pubs.usgs.gov/publication/ofr03351},
  note = {Source identifier: ofr03351}
}