Burnham, J.B. & Stewart, D.H. Foreign and domestic discussions on natural geothermal power and potential use of Plowshare to stimulate these natural systems, report, July 6, 1971; (https://digital.library.unt.edu/ark:/67531/metadc1054430/m1/1/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .