For all at once there arose a peculiar rushing sound, and as everyone crouched as low as he could, he was conscious of the whistling of wings in rapid flight and the ammoniacal odour of a great stream of birds passing over them to reach the outlet from the passage into the open air. "It's all right, lads," shouted Briscoe. "It's only a flock of oil-birds that we have disturbed. Yes, I thought so: some of them have helped to block up these window places with their nests. I can feel several here." The birds were some minutes before they had all passed through the opening, and then the tramp downwards was resumed, with the result that before long the light grew stronger from below, and at last quite bright, for a peculiar rustling was heard, which resolved itself into the acts of Brace, who had reached a level spot and was now busy with his large sheath-knife hacking away at a dense mass of creeper not unlike ivy. A few minutes later, and he was out upon an overgrown terrace gazing over a much-corroded carved parapet at the sparkling river below; and he uttered a loud cheer and stood waving his hat to the men far down to his left, two of whom were seated in the larger boat. The top terrace of the great temple-like place had been reached, and after a few words of congratulation upon their success the examination of the strange edifice began. They were a good deal checked at first by the growth of ages and stones which had crumbled down; but they were not long making out that the construction of the place was upon the same plan as that put in practice over the openings to right and left; though the cells were much smaller, and suggested that they had been intended for occupation by one or at most two people. There were no traces of domestic implements to be found, and nothing but the dust of the crumbling stones and the nests of birds with which the openings of the cells were choked met the searchers' eyes. The investigation of this portion of the cliff city was, of course, made in the reverse way, terrace after terrace being explored by the adventurers descending; but the L-shaped shafts were far larger and more commodious, and, instead of holes being made for the feet, carefully-made steps had been cut out of the solid stone. Feeling assured that if any interesting traces of the old dwellers were to be found they would in all probability be here, Sir Humphrey and his brother headed the search, and one by one every cell was entered and each terrace explored, till, as they looked over the front, they made out that only three more terraces remained, one of which was that below which the great wall of rock went sheer down to the river at the spot where they had cast the line to find bottom. The party paused now for a few minutes' rest and conversation before descending to these last three terraces.