In his hurry his foot slipped and he fell backward to the ground. Just above him there burst out a flash, and a heavy report instantly followed. Sandy knew what it meant, and that his faithful brother was firing at the advancing pack in order to stop their rush. He struggled to his feet, and commenced once more to clamber up the rude fortification, at the same time shouting at the top of his voice. This was done with a purpose, for he understood full well that, like most cowardly animals, wolves greatly fear the voice of man. Bob, too, was exerting himself to the utmost. Again came that tremendous crash, as the second musket was discharged close to Sandy's ear. Then an eager hand laid hold of him, and he felt himself dragged over the topmost log! Both boys were panting for breath, but, thrusting one gun into Sandy's hands, Bob started to hastily reload the other. They could hear their enemies not ten feet away, snarling and snapping terribly. It needed no explanation to tell Sandy what was going on out there in the snow; for he knew that wolves are cannibals if pressed with hunger. "It was a pretty close shave, Bob!" he exclaimed, after he had rammed a bullet home in his gun, and fixed the priming in the pan. "And a foolhardy act," returned the other, gravely. "If you had missed your footing a second time you would have been pulled down in spite of all I could do, and that would have been the end of us." Sandy felt abashed. He knew perfectly well that he had been guilty of a reckless feat that might have cost both of them their lives; for without doubt Bob would have leaped over the barrier to his assistance, and shared his sad fate. Perhaps thoughts of the dear ones at home, who would have mourned them so grievously, may have caused the boy to resolve upon a wiser course the next time he found himself tempted to take hazardous chances. They stood on guard, and waited to see what their enemies would do when they had finished their meal. "I hope they will go away, and leave us alone," said Sandy, uneasily. "That would be almost too good to be true," remarked Bob, who knew more about the habits of animals than his brother. "Instead, I fear that the taste of food they have had will only make them more savage." "Look! they are beginning to creep closer again!" exclaimed Sandy, a minute later, with a feeling of renewed uneasiness. "Then we had better begin to shoot again, and make every bullet count. Let me start the ball rolling, boy," said Bob, as he picked out a dark form advancing slowly over the white snow. Resting his musket across the upper log, he took a careful aim and fired. With the report a series of howls burst forth, and many forms were seen dashing this way and that. Some fled, only to come back again when they scented a new feast, and in another minute the wolf that had fallen before the gun of the young pioneer was affording his mates an additional scrap of dinner.