@misc{indiciae32c1d63ab8c7,
  title = {Block diagrams},
  author = {W. D. Johnston and B. Thomas Nolan},
  year = {1938},
  doi = {10.2113/gsecongeo.33.1.107},
  url = {https://pubs.usgs.gov/publication/70212720},
  note = {Source identifier: 70212720}
}