What is the author's tone in The Exploration of the Colorado River and Its Canyons by John Wesley Powell?

The tone of the book is basically objective. Powell viewed himself as a scientist on a scientific expedition. His goal was to chart the last unmapped territory in the United States, and this he did. As they charted the unexplored territory, Powell maintained a detailed journal and the book contains daily entries from his records, describing what they did, what they saw and what they experienced.