@misc{indiciaed8042ccc40bf,
  title = {Spirit leveling in Illinois, 1896-1942. Part 1, Southern Illinois},
  author = {Members of the Engineering Geology and Ground Water Branches, U.S. Geological Survey},
  year = {1942},
  doi = {10.3133/b930a},
  url = {https://pubs.usgs.gov/publication/b930A},
  note = {Source identifier: b930A}
}