Correspondence, writings, photograph albums, photographs, etc., dating primarily from the last thirty years of Ayer's life. Ayer Collection related papers include correspondence between Ayer, Ayer librarians and curators Clara Smith and Ruth Lapham Butler, and prominent historians, writers, librarians, and collectors (Ballou, Engelhardt, Hodge, Lummis, Nute, Robertson, Thwaites, Victor, Wagner, etc.) and collection lists, (c.1900). Personal correspondence is primarily greetings from family, friends, and associates, but also contains letters concerning Ayer's association with the Field Museum and the Board of Indian Commissioners. Ayer's western travels and automobile trips to North Africa and Europe are documented in his writings and the photograph albums containing snapshots and panoramic views taken by his wife, Emma Burbank Ayer.