@misc{indiciae05edb6cb1c43,
  title = {The logic of geological maps, with reference to their interpretation and use for engineering purposes},
  author = {David J. Varnes},
  year = {1974},
  doi = {10.3133/pp837},
  url = {https://pubs.usgs.gov/publication/pp837},
  note = {Source identifier: pp837}
}