At intervals on the tops of the outer walls which enclosed this court were placed watch-towers, of forty and sixty feet in height. The thickness of the portal through which they had passed was twenty feet at the base and about ten at the top, as nearly as they were able to calculate from below. An open gateway within the most massive of the buildings attracted their attention, but before venturing to explore its dark cavity, Ned formed his company into a close square; then, bidding them wait and watch, he ran over to the wall on the other side, and, climbing it by some steps, he stood on the esplanade with about five feet of wall in front of him. Then as he looked over he uttered a cry that quickly brought Fred, Clarence, and Cocoeni to his side. They were overlooking a vast desert that spread far as the eye could take in, as bare and tawny as the great Sahara. This wall had been built upon a giddy precipice, without a break or a ledge. As they stretched over they could have dropped a stone without striking anything until it reached the bottom, four thousand feet at least from where they stood. The air was bracing, and would have been cool, only for the intense waves of heat that were wafted up from the burning sands. "Here terminates our journey, I expect, Ned?" said Fred, in mildly interrogative tones. Ned had pulled out his field-glass, and was scanning the far-distant horizon through it, therefore he did not answer at once. It was a splendid instrument, and of exceptionally far-reaching power of lens. "Tell me, Fred and Clarence, what you see over there?" he asked, handing the glass to his companions. "Look carefully before you speak, and let Cocoeni have a peep as well first, before you open your mouths." When Fred had looked through it for some moments he handed the glass to Clarence, who in his turn gave it to Cocoeni in silence. Then the three friends glanced at each other dubiously. "Well, Cocoeni, you say first what you saw." "What white man calls mirage, and black man calls devil-land," replied Cocoeni, grimly. "Well, but describe this mirage." "I saw trees and water and big houses same as this here, all shimmering in the air." "Yes; but they were only in one part of the horizon--to east and west there was nothing but sand." "That is so, baas." "And what did you see, Clarence?" "Oh, something the same as Cocoeni. There appeared to be a large lake in one part, with trees and houses on its margin." "And you, Fred?" "Oh, I saw the lake, or sea, with the other deceptions," replied Fred. "But I have seen the same sort of thing in Australia." "I bet you didn't, Fred, see exactly the same sort of thing out there!" cried Ned, excitedly. "Now, you know, the nature of mirages is that they will show up on all sides when they show at all. Look again, and see if that lake has altered its position, or if it is repeated anywhere else than in the one direction."