George Bird Grinnell books are all PD I think
George Bird Grinnell (September 20, 1849 – April 11, 1938) was an American anthropologist, historian, naturalist, and writer. Grinnell was born in Brooklyn, New York, and graduated from Yale University with a B.A. in 1870 and a Ph.D. in 1880. Originally specializing in zoology, he became a prominent early conservationist and student of Native American life. Grinnell has been recognized for his influence on public opinion and work on legislation to preserve the American buffalo.
http://en.wikipedia.org/wiki/George_Bird_Grinnell