Leaving all traces of man behind them, the two climbed a rugged path, and entered a cañon, through the center of which roared a foaming torrent, and which was so deep and sheltered that even at this noon-hour the path was cool and the sunlight tempered. As they walked or clambered on, both men gradually grew silent. Of what Dr. Seltzer might be thinking Mr. Burton did not know--his own mind was absorbed in the scene which he was awaiting the earliest fitting moment to enact. The doctor, who should have acted as guide, had, somehow, chanced to lag behind. "Which direction shall I take?" asked Mr. Burton, presently. "Ascend the narrow defile to the right," called out his companion, pressing after him, "but be cautious of your footing. A misstep may hurl you upon the rocks below. In three minutes we shall be in a safe and beautiful region, with our feet, literally, treading a silver floor." As he spoke thus, he drew nearer, but the path was too narrow to allow him to take the advance, and Mr. Burton continued to lead the way. The subtle perceptions of the detective, a magnetism which amounted almost to the marvelous, I have so frequently referred to, that my reader will understand how it was that Mr. Burton, thus in the van, and not looking at all at his companion, felt a curious, prickly sensation run along his nerves. He came to the narrowest part of the dangerous path. An immense rock reached up, a mighty wall, upon the right, and to the left, far below the uneven, stony and brier-grown ledge along which he was picking his steps, foamed and roared the torrent, over rocks which thrust themselves here and there above the yeasty water. Directly in front arose an obstacle in the shape of a projection of the rock some three or four feet in hight, covered with tough little bushes, one of which he took hold of to draw himself up by. However, instead of pulling himself up, as his action seemed to indicate that he was about to do, he turned and grasped the arm of Dr. Seltzer. His movement was rapid as lightning, but it was not made a moment too soon. The arm which he held in a clasp of steel was raised to strike, and a Spanish dirk was in the hand. A stealthy, murderous light, almost red in its intensity, burned in the eyes which now sunk before his. An instant the foiled assassin stood surprised; then commenced a struggle between the two men. Dr. Seltzer made desperate efforts to hurl his antagonist into the torrent beneath; but, though frantic with rage and hate, his violent exertions did not effect their object. On the contrary, Mr. Burton, calm and self-possessed, despite an instant's astonishment, pressed his adversary backward along the narrow path until they were both on safe ground, in the middle of a little grassy plateau, which they had lately traversed, where he held him, having disarmed him of his knife.