@misc{indiciae13c790080e64,
  title = {A reconnaissance study of the beach sands of Puerto Rico},
  author = {Robert B. Guillou and Jewell J. Glass},
  year = {1957},
  doi = {10.3133/b1042i},
  url = {https://pubs.usgs.gov/publication/b1042I},
  note = {Source identifier: b1042I}
}