"Perspectivas petroliferas mundiales, desde un punto de vista geologico" Hollis D. Hedberg, Instituto Geologico y Minero de Espana, Numero 39, Box: 10, Folder: 35. Hollis Hedberg papers, RH MS 546. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/149257 Accessed May 24, 2024.