What does the description of life with the mail train?

The work is now strict and heavy, as they are pulling the mail carts back over the trail to Dawson. Life is monotonous. Feeding time is the focus of each day. Buck quickly achieves mastery over the other dogs. He loves to sit in front of the fire and dream. Sometimes he dimly recalls memories from his California home. More often, he is visited by visions of an ancient life, his place with ancient humans. He sometimes thinks he sees a man, different from men today, and he remembers the rustle of beasts and the readiness for the fight.