United States. Bureau of Labor Statistics. "Hours and Earnings in Anthracite and Bituminous Coal Mining, 1922 and 1924 : Bulletin of the United States Bureau of Labor Statistics, No. 416,"
Wages and Hours of Labor in Bituminous-Coal Mining
(September 1926).
https://fraser.stlouisfed.org/title/4021/item/493203, accessed on February 15, 2025.