@misc{indiciae4201d8a5d51c,
  title = {Time drill; an introduction to geologic time},
  author = {Kevin P. Purcell},
  year = {1995},
  doi = {10.3133/ofr95805b},
  url = {https://pubs.usgs.gov/publication/ofr95805B},
  note = {Source identifier: ofr95805B}
}