@misc{indiciaebe882a161f07,
  title = {Definition and world resources of natural bitumens},
  author = {R. F. Meyer and Wallace De Witt},
  year = {1990},
  doi = {10.3133/b1944},
  url = {https://pubs.usgs.gov/publication/b1944},
  note = {Source identifier: b1944}
}