United States. Bureau of Labor Statistics. "Wage Chronology: Bituminous Coal Mines, 1933-68 : Bulletin of the United States Bureau of Labor Statistics, No. 1558,"
Wage Chronology: Bituminous Coal Mine Operators and United Mine Workers of America
(1967).
https://fraser.stlouisfed.org/title/4650/item/498302, accessed on April 27, 2025.
@FedFRASER