" They struggled on. By the time the sun dipped below the horizon again it had become, as Olsen had prophesied, a little easier: there were stretches of as much as a hundred yards where the sledges could be pulled without having to be lifted or coaxed up or down slopes. But it was hard enough; their muscles were unaccustomed to the tasks they now had, and as the day wore on they were tiring. "

― John Christopher , The White Voyage