Materials from various persons used by O. T. Mason in Smithsonian Annual Reports, 1874 - 1879 & 1881 - 1883.
1) Most have been published (although not necessarily verbatim). unpublished letters and maps include: Mitchell, Augustus to Joseph Henry, August 24, 1873. "Crude Thoughts on American Indians." Discusses visit of P. Pitchlynn to author at Portland, Me., 1846. 2) Bruff. J. Goldsborough to Joseph Henry, February 10, 1873. concerning human face carved on rock near Chain Bridge, Potomac River. 3) Trowbridge, David, December 14, 1876 "Ancient Fort and Burial Ground". with map (area of Waterburgh, New York).