What is the author's style in Jim Bridger, Mountain Man; a Biography by Stanley Vestal?

The perspective of the book is a view of the American frontier through the eyes of Jim Bridger and told in the third person point of view. At the beginning of the book, the reader feels the energy of an 18-year-old young man who is desperately trying to be recruited to Major Henry's expedition. As Jim ages and becomes more experienced, this perspective also changes, as when Jim becomes an independent trapper and takes on added responsibilities.