Amending the Mineral Leasing Act of 1920 and for the relief of Keith C. Hayes and Dorothy Smith : hearing before the Subcommittee on Energy Resources and Materials Production of the Committee on Energy and Natural Resources, United States Senate, Ninety-sixth Congress, second session, on S. 1455, a bill to further amend the Mineral Leasing Act of 1920 (30 U.S.C. 201 (a)) to authorize the Secretary of the Interior to exchange federal coal leases and to encourage recovery of certain coal deposits, and for other purposes : S. 1529, a bill for the relief of Keith C. Hayes and Dorothy Smith, April 15, 1980