But if the dogs had their tricks, Thor also had his.  After three or four vain rushes, in which the Airedales eluded him by their superior quickness, he backed slowly toward the huge rock beside which Muskwa was crouching, and as he retreated the dogs advanced.

Their increased barking and Thor’s evident inability to drive them away or tear them to pieces terrified Muskwa more than ever.  Suddenly he turned tail and darted into a crevice in the rock behind him.

Thor continued to back until his great hips touched the stone.  Then he swung his head side wise and looked for the cub.  Not a hair of Muskwa was to be seen.  Twice Thor turned his head.  After that, seeing that Muskwa was gone, he continued to retreat until he blocked the narrow passage that was his back door to safety.

The dogs were now barking like mad.  They were drooling at their mouths, their wiry crests stood up like brushes, and their snarling fangs were bared to their red gums.

Nearer and nearer they came to him, challenging him to stay, to rush them, to catch them if he could—­and in their excitement they put ten yards of open space behind them.  Thor measured this space, as he had measured the distance between him and the young bull caribou a few days before.  And then, without so much as a snarl of warning, he darted out upon his enemies with a suddenness that sent them flying wildly for their lives.

Thor did not stop.  He kept on.  Where the rock wall bulged out the trail narrowed to five feet, and he had measured this fact as well as the distance.  He caught the last dog, and drove it down under his paw.  As it was torn to pieces the Airedale emitted piercing cries of agony that reached Bruce and Langdon as they hurried panting and wind-broken up the slide that led from the basin.

Thor dropped on his belly in the narrowed trail, and as the pack broke loose with fresh voice he continued to tear at his victim until the rock was smeared with blood and hair and entrails.  Then he rose to his feet and looked again for Muskwa.  The cub was curled up in a shivering ball two feet in the crevice.  It may be that Thor thought he had gone on up the mountain, for he lost no time now in retreating from the scene of battle.  He had caught the wind again.  Bruce and Langdon were sweating, and their smell came to him strongly.

For ten minutes Thor paid no attention to the eight dogs yapping at his heels, except to pause now and then and swing his head about.  As he continued in his retreat the Airedales became bolder, until finally one of them sprang ahead of the rest and buried his fangs in the grizzly’s leg.

This accomplished what barking had failed to do.  With another roar Thor turned and pursued the pack headlong for fifty yards over the back-trail, and five precious minutes were lost before he continued upward toward the shoulder of the mountain.