@misc{indiciae2c3c50d0d842,
  title = {Maps showing areal extent of selected Paleozoic shales in the northern Midcontinent, U.S.A.},
  author = {W. P. Pratt},
  year = {1992},
  doi = {10.3133/mf1835h},
  url = {https://pubs.usgs.gov/publication/mf1835H},
  note = {Source identifier: mf1835H}
}