Sometimes on the wind came a low thunder.

Was it a storm or an avalanche slipping or falling water?
He could not tell.

The sound was significant and haunting.
Of one thing he was sure--that he could not have found his back-trail.
But he divined he was never to retrace his steps on this journey.

The stretch of broken plateau before him grew wilder and bolder of outline, darker in color, weirder in aspect, and progress across it grew slower, more dangerous.

There were many places Nagger should not have been put to--where a slip meant a broken leg.