A second cold snap came on, but cold or warm it was all the same, an unbroken trail.

When the thermometer went down to fifty below, it was even harder to travel, for at that low temperature the hard frost-crystals were more like sand-grains in the resistance they offered to the sled runners.

The dogs had to pull harder than over the same snow at twenty or thirty below zero.

Daylight increased the day's travel to thirteen hours.

He jealously guarded the margin he had gained, for he knew there were difficult stretches to come.
It was not yet quite midwinter, and the turbulent Fifty Mile River vindicated his judgment.