The river swirled on through the heat, the sweltering, fever-breathing heat. The long, deep reach made but scant murmur, save where the boughs of a luxuriant vegetation dipped on its surface. Above, on either hand, masses of rolling verdure, tall forest trees, undergrowth in rich profusion, and, high up against the blue sky, battlemented rock walls. Two dark objects relieved the shimmering smoothness of the surface of the reach-two minute dark objects to the ordinary observer, afloat, motionless. Yet why should these remain motionless instead of floating down with the fairly strong, though smooth, current? Well, there might have been, behind each, about twelve feet of ugly, scaly saurian, whose powerful under-water stroke kept them stationary, while watchful, against the descending stream.