There are 94 boxes of the scientific papers of Robert E. Horton's papers in the US National Archives. In Box 71, there are copies of letters exchanged between LeRoy K. Sherman, Consulting Engineer of Chicago, IL (and author of the classic paper on the unitgraph) and Robert E. Horton, Consulting Hydraulic Engineer of Voorheesville, NY, concerning rapid rises of groundwater levels in near-stream wells and their relationship to the storm hydrograph. They provide an interesting insight into the views of both Sherman and Horton on controls on stream flow generation, and the relationship between Horton and other hydrologists. Horton's analysis of subsurface flow processes and saturated areas anticipates later analyses of topographic controls on hydrological responses.