Tunneling-Machine., patent, December 30, 1919; (https://texashistory.unt.edu/ark:/67531/metapth1259501/m1/1/: accessed June 22, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu.; .
Tunneling-Machine., patent, December 30, 1919; (https://texashistory.unt.edu/ark:/67531/metapth1259501/m1/1/: accessed June 22, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu.; .