Series Is Presented Here As Two Variables-(1)--Original Data, 1921-1929 (2)--Original Data, 1929-1949. The Indexes Compiled By The Federal Reserve Bank Of Philadelphia Are Based On Sample Figures Obtained From The Anthracite Institute. Source: The Original Indexes For This Series Are Based On 1923-1925=100 In The Table Furnished By The Federal Reserve Bank Of Philadelphia; The Indexes Of The Department Of Research Were Converted By NBER To A 1929=100 Base
This NBER data series m08249a appears on the NBER website in Chapter 8 at http://www.nber.org/databases/macrohistory/contents/chapter08.html.
NBER Indicator: m08249a
Release: NBER Macrohistory Database
National Bureau of Economic Research, Index of Employment, Anthracite Mining for United States [M0849AUSM340NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M0849AUSM340NNBR/, September 1, 2015.