By this time Roger was fully alive to the difficulties that confronted him. If he were out of reach of the party, and could not make himself heard, it would be very difficult to trace them, even if he crossed their trail; unless it were where they had been making a sight or where undergrowth had been cut, there would be no mark of their passage, as the soft ground speedily sucked in all trace of footsteps. A shot, he thought, would travel farther than the voice, and so, taking out his revolver, the boy fired three times in the air. He strained his ears eagerly, though fearing that no shot would answer, but when the minutes passed by he knew that he was lost and that he would have to find his way back to the party unaided. But one thing remained to be done. He must retrace his steps, trusting to his new-born knowledge of woodsmanship to lead him aright, back to the place where he had gained the ridge of ground from the shallow lake, then cross that, if he could remember the direction, and he would be but twenty yards or so from the path the party must have traveled. He would be a couple of hours behind them, of course, but if he could strike their trail he was bound to overtake them some time that night. There was no other alternative, he must endeavor to find them, even at the risk of becoming still more enmeshed in the mazes of the swamp. Limping back over the ridge of ground, his ankle growing sorer each step, Roger painfully wended his way to the little lake. He found the ridge, but in returning it appeared to divide into twain paths, and for a moment his heart sank within him; as luck would have it, however, he remembered seeing a tree that had been struck by lightning somewhere about where he then was, and he determined to go along each of the paths until he struck the tree. Taking the left hand, at random, he hobbled along for half an hour, but seeing no blighted tree, retraced his way and took the other path. Just as he was about to give up that route also, in despair, the sentinel tree on which he had been building loomed up before him. It was the first sure sign that he was on the right trail, and Roger let out a boyish whoop of delight. Suddenly he thought he heard an answering yell, and he called again, but there being no answer he felt that his ears had deceived him. Soon he came to the banks of the little shallow lake, and struck in to wade across. [Illustration: A TANGLE OF SWAMP. Conditions which must be overcome by topographic parties, though "too wet for walking, too dense for boats." _Photograph by U.S.G.S._]