@misc{indiciae05ad3dfd4ce4,
  title = {Progressive regional metamorphism of the lower kittanning coal bed of western Pennsylvania},
  author = {T. Stadnichenko},
  year = {1934},
  doi = {10.2113/gsecongeo.29.6.511},
  url = {https://pubs.usgs.gov/publication/70221659},
  note = {Source identifier: 70221659}
}