@misc{indiciae37adf7d0387f,
  title = {Proterozoic crustal boundary in the southern part of the Illinois Basin},
  author = {Paul C. Heigold and Dennis R. Kolata},
  year = {1993},
  doi = {10.1016/0040-1951(93)90012-9},
  url = {https://pubs.usgs.gov/publication/70018264},
  note = {Source identifier: 70018264}
}