@misc{indiciae8c17ee2f7cf2,
  title = {Contour map of the base of the Pennsylvanian system, eastern Kentucky},
  author = {T.D. Coskren and C. L. Rice},
  year = {1979},
  doi = {10.3133/mf1100},
  url = {https://pubs.usgs.gov/publication/mf1100},
  note = {Source identifier: mf1100}
}