"The History of the American Indians" by James Adair
Published 1775 by Edward and Charlrs Dilly, London
James Adair 1709-1783, was a trader among the southeast Indians for 40 or so years before the revolution. He married a Chickasaw woman and had children.
This book is the authoritative text on the southeast Indians at the time of contact. I havnt made it through it all, but it contains many insights I to Native American life, language, medicine, religion and customs. At the time many white people were advocating wholesale genocide of the Indians. Adair respected them, it comes through in his writing.
He also had a theory which may sound crazy today, that the Indians descended from the Israelites. Of course he didn't have advanced science at his disposal. He based his theory on they're language, religion, amoung other things, and defends it eligently in the book. In fact I believe there's at least one eastern tribe which still believes this.