With an anxious glance at his white face, Audubon nodded and broke into the trees, for they were already on the knoll. Norton leaned back, faint and giddy, and as his eyes fell on the trail he noted idly that it was hard rocky soil, indented with the unmistakable marks of horseshoes. In his present state of mind this conveyed nothing to him; a settler might have passed along by the trail, or any wandering pedlar might have made the tracks. He leaned back and closed his eyes, utterly relaxing himself and grateful for the brief rest. He seemed to ache all over, and for almost the first time in His life his whole body seemed wearied and fatigued. A strange lassitude had come over him. "Norton!" At the excited whisper he opened his eyes and sat up, to see Audubon peering through the bushes, finger on lip. The other beckoned hastily. "Come in here! Be cautious." Already refreshed by his rest, Norton crept into the bushes. Audubon's excited eagerness put him on the alert at once, and he stole after the other with all the silent care of an Indian. Reaching a densely overgrown covert, Audubon paused and held up a hand, listening. From above there came a low trilling bird-song, but Norton could make out nothing else. "What is it, man? What did you find?" "Listen!" whispered Audubon softly. "Isn't it like a goldfinch singing under its breath? The same little trills, the same sustained sweet notes in between--but it's a vireo, Norton! Would you guess it?" Norton stared, but his friend was in deadly earnest. He heard the hidden bird change its song suddenly, and Audubon gripped his arm hard. "There--that's the real vireo song, with the pulse-like, clear-cut notes! Did you ever hear such a thing before? That bird was giving a real goldfinch trill, man----" "Where's the cottonwood?" broke in Norton drily. The other looked at him, his face blank on a sudden. "Why--why--I clear forgot----" Norton laughed, but Audubon suddenly gripped his arm harder. The bird above had broken off in mid-song, for no apparent reason. From somewhere outside the covert came the rattle of a stone, followed by a horse's snort. "Keep quiet," breathed Norton, looking into the deep eyes of his friend. "Someone's on the trail." Audubon nodded, and the two men stood tense and motionless, every nerve on edge. With startling abruptness there came a deep curse from the trail. "Damn it, pull up! I ain't no Injun!" There followed a chuckle in another voice--one that sent Norton's hand to his rifle. "Winded, Abel? Well, there's no haste. What did that boat put in for?" "How'n tarnation do I know?" growled the first. "Wa'n't none o' our boys on her." "So much the better for her, then," laughed the second. "It's odd we didn't meet Tobin, Abel!" A grunt replied. Norton glanced at his friend, his brown eyes aflame. "Duval," he murmured under his breath. "Who's the other? Abel Grigg?" Audubon nodded quickly, and his face was set in eager surmise.