United States. Bureau of Labor Statistics. "Hours and Earnings in Anthracite and Bituminous Coal Mining: Anthracite--1919 and 1920, Bituminous--1919 : Bulletin of the United States Bureau of Labor Statistics, No. 279," Wages and Hours of Labor in Bituminous-Coal Mining (April 1921). https://fraser.stlouisfed.org/title/4021/item/493033, accessed on November 19, 2024.