@misc{indiciae2386e75b617f,
  title = {Clays and shales of Minnesota},
  author = {Frank F. Grout and Edgar Kirke Soper},
  year = {1919},
  doi = {10.3133/b678},
  url = {https://pubs.usgs.gov/publication/b678},
  note = {Source identifier: b678}
}