Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Muir's glacier voyages

No doubt about it, John Muir was one of America's greatest citizens. He founded the Sierra Club and was instrumental in starting the ecological movement in the United States. In this book Muir recounts three journeys to Southeast Alaska that he took in the late 1800's. He writes better about glaciers than any writer who ever lived. There are flaws: Muir's attitudes about native peoples are simple-minded and ignorant, and his prose is sometimes dry and dull. Also, one cannot help but call Muir's credibility into question when he writes than he and his dog Stickeen walked fifteen miles across a crevasse-riddled glacier in three hours and then had nothing for dinner but a moldy cracker. But these are important records from a man who truly loved the natural world, and it's essential reading material for anyone traveling to Southeast Alaska or anyone wishing to learn more about glaciers.