@misc{indiciae80c59818bddc,
  title = {Geology and fluorspar deposits, Big Four fault system, Crittenden County, Kentucky},
  author = {George C. Hardin and Robert Denny Trace},
  year = {1959},
  doi = {10.3133/b1042s},
  url = {https://pubs.usgs.gov/publication/b1042S},
  note = {Source identifier: b1042S}
}