References
- Carlson , C. G. 1972 . “ Stratigraphic position of lignite beds in the Tertiary rocks of Mercer and Oliver counties ” . In Depositional environments of the lignite‐bearing strata in western North Dakota , North Dakota Geol. Survey, Misc. Set. 50 Edited by: Ting , F. T. C. 95 – 104 .
- Schopf , J. M. 1970 . Petrified peat from a Permian coal bed in Antarctica . Science , 169 ( 3942 ) : 274 – 277 .
- Ting , F. T. C. 1972 . Petrified peat from a Paleocene lignite in North Dakota . Science , 177 : 165 – 166 .