@misc{indiciae56b13676ca52,
  title = {Aeromagnetic map of the Elverson quadrangle, Berks and Chester Counties, Pennsylvania},
  author = {Randolph Wilson Bromery and John R. Henderson and G. L. Zandle},
  year = {1959},
  doi = {10.3133/gp221},
  url = {https://pubs.usgs.gov/publication/gp221},
  note = {Source identifier: gp221}
}