@misc{indiciae0fa3d5955745,
  title = {Big Snowy and Amsden groups and the Mississippian-Pennsylvanian boundary in Montana},
  author = {E. K. Maughan and A. E. Roberts},
  year = {1967},
  doi = {10.3133/pp554b},
  url = {https://pubs.usgs.gov/publication/pp554B},
  note = {Source identifier: pp554B}
}