@misc{indiciae580d2ac464ed,
  title = {Bedrock geologic map of the Pepperell, Shirley, Townsend quadrangles, and part of the Ayer Quadrangle, Massachusetts and New Hampshire},
  author = {G.R. Robinson},
  year = {1978},
  doi = {10.3133/mf957},
  url = {https://pubs.usgs.gov/publication/mf957},
  note = {Source identifier: mf957}
}