Nothing was too great for Buck to do, when Thornton commanded.

One day (they had grub-staked themselves from the proceeds of the raft and left Dawson for the head-waters of the Tanana) the men and dogs were sitting on the crest of a cliff which fell away, straight down, to naked bed-rock three hundred feet below.

John Thornton was sitting near the edge, Buck at his shoulder.

A thoughtless whim seized Thornton, and he drew the attention of Hans and Pete to the experiment he had in mind.

"Jump, Buck!" he commanded, sweeping his arm out and over the chasm.