United States. Bureau of Labor Statistics. "Hours and Earnings in Bituminous Coal Mining, 1922, 1924, and 1926 : Bulletin of the United States Bureau of Labor Statistics, No. 454," Wages and Hours of Labor in Bituminous-Coal Mining (1927). https://fraser.stlouisfed.org/title/4021/item/493204, accessed on November 19, 2024.