@misc{indiciae601d99ae7151,
  title = {Index maps of the Wisconsin-Illinois-Iowa lead-zinc mining district},
  author = {A.V. Heyl and E.J. Lyons and A.F. Agnew and A. E. Flint and R.P. Crumpton},
  year = {1951},
  doi = {10.3133/ofr5168},
  url = {https://pubs.usgs.gov/publication/ofr5168},
  note = {Source identifier: ofr5168}
}