@misc{indiciae1b874c917cbb,
  title = {Colored gravity anomaly and terrain maps of the northeastern United States and adjacent Canada; a description of colored slides},
  author = {Robert W. Simpson and Richard H. Godson and Wallace A. Bothner},
  year = {1981},
  doi = {10.3133/ofr81560},
  url = {https://pubs.usgs.gov/publication/ofr81560},
  note = {Source identifier: ofr81560}
}