@misc{indiciae6a09c06e69e9,
  title = {Results of spirit leveling in Delaware, District of Columbia, Maryland, and Virginia, 1896 to 1909, inclusive},
  author = {Robert Bradford Marshall},
  year = {1910},
  doi = {10.3133/b434},
  url = {https://pubs.usgs.gov/publication/b434},
  note = {Source identifier: b434}
}