@misc{indiciaec46e55ee3ca9,
  title = {Fifty-second annual report of the Director of the Geological Survey},
  author = {George Otis Smith},
  year = {1931},
  doi = {10.3133/ar52},
  url = {https://pubs.usgs.gov/publication/ar52},
  note = {Source identifier: ar52}
}