@misc{indiciae3ef826a6c700,
  title = {Analyses of coal samples from various fields of the United States},
  author = {M. R. Campbell},
  year = {1914},
  doi = {10.3133/b541k},
  url = {https://pubs.usgs.gov/publication/b541K},
  note = {Source identifier: b541K}
}