@misc{indiciae7c64b11e7be1,
  title = {The upper Mississippi Valley zinc-lead district; In two parts: I General structural relations of the upper Mississippi Valley zinc-lead district. II. The ore deposits of the upper Mississippi Valley zinc-lead district},
  author = {Allen V. Heyl},
  year = {1950},
  doi = {10.3133/ofr5013},
  url = {https://pubs.usgs.gov/publication/ofr5013},
  note = {Source identifier: ofr5013}
}