Chiefly correspondence; together with manuscripts of writings, reprints, notes, reports, records of earthquakes and epicenters, and copies of the publication Volcano Letter (1934-1940). Includes large groups of correspondence with Carnegie Institution of Washington (relating to the establishment of a central station for seismological investigation), with Seismological Society of America (relating to mapping earthquake faults in the U.S., recording earthquakes, and establishing safe building codes), and with U.S. Coast and Geodetic Survey (exchanging seismological data). Includes material relating to the earthquake situation in southern California and correspondence with George Louderback relating to the 1857 earthquake. Other correspondents include various seismological observatories and manufacturers of instruments and equipment for seismological laboratories.