Here are some links to old writings. The first is "A tour of four great rivers...the journal of Richard Smith" by Francis W. Halsey. It contains two references to burning.
The second is from "History of Pittsburgh and environs" by George Thornton Fleming
Incidentally, Thomas Ashe "Travels in America" looks like fine reading as well.
Next are two different writings about some strange, ancient stone walls. First is from "American architect and architecture, Volume 11"
Second is "A New and Popular Pictorial Description of the United States" by John A. Lee & Co.