The author provides no first-hand knowledge of his own, providing only second-hand synopses of the works of others.
If you are willing to research further, this would seem to provide a ready-made outline. My interest in buying the book was for possible linguistic comparison, but the author only names a few native gods and gives very little in the native languages.
The author prides himself in identifying his allegience to French methodology. Evidently this explains his negligent lack of maps, glossary, charts, or any detailed descriptions of concrete facts.