Upton, William F. [Letter from William F. Upton to A.L. Matlock, September 7, 188?], letter, 188u-09-07; (https://digital.library.unt.edu/ark:/67531/metapth186882/m1/1/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .