@misc{indiciae1441fcc179f1,
  title = {The Geology of the Upper Mississippi Valley Zinc-Lead District},
  author = {Allen V. Heyl and Allen F. Agnew and Erwin J. Lyons and Charles H. Behre and Arthur E. Flint},
  year = {1959},
  doi = {10.3133/pp309},
  url = {https://pubs.usgs.gov/publication/pp309},
  note = {Source identifier: pp309}
}