@misc{indiciae4d9bec33166a,
  title = {Results of spirit leveling in Illinois, 1911 to 1913, inclusive},
  author = {Robert Bradford Marshall},
  year = {1914},
  doi = {10.3133/b553},
  url = {https://pubs.usgs.gov/publication/b553},
  note = {Source identifier: b553}
}