@misc{indiciae6f5cfbd8bec8,
  title = {Aeromagnetic and generalized geologic map of southeastern Pennsylvania},
  author = {R. W. Bromery and Andrew Griscom},
  year = {1967},
  doi = {10.3133/gp577},
  url = {https://pubs.usgs.gov/publication/gp577},
  note = {Source identifier: gp577}
}