@misc{indiciae99e2aef63744,
  title = {Graptolites from the Martinsburg Formation, Lehigh Gap, Eastern Pennsylvania},
  author = {Jack Burton Epstein and William B. N. Berry},
  year = {1973},
  url = {https://pubs.usgs.gov/publication/70159644},
  note = {Source identifier: 70159644}
}