@misc{indiciaecdcb6a6f4eaa,
  title = {Results of spirit leveling in Illinois, 1909 and 1910},
  author = {Robert Bradford Marshall},
  year = {1911},
  doi = {10.3133/b493},
  url = {https://pubs.usgs.gov/publication/b493},
  note = {Source identifier: b493}
}