@misc{indiciaef878398ff6a9,
  title = {The valuation of public coal lands: The value of coal land; Depth and minimum thickness of beds as limiting factors in valuation},
  author = {George H. Ashley and Cassius Fisher},
  year = {1910},
  doi = {10.3133/b424},
  url = {https://pubs.usgs.gov/publication/b424},
  note = {Source identifier: b424}
}