They were about to give it up and go away, when Jack suddenly uttered a cry. ’See! What is that on the floor!’ he exclaimed. ’Ah, I thought so! A diamond—a small diamond!’ He exhibited upon the open palm of his hand a little sparkling stone. While his companions were busy looking at it, he went on to examine attentively a number of slabs of carved marble which stood up from the floor some four or five feet, forming a many-sided enclosure. They made a ring, as it were, fifteen feet in diameter or thereabouts, and upon each slab were figures or scenes carved in bas-relief. It was not unlike a huge, many-sided flower-pot; and it appeared to be intended for a similar purpose; for the space it enclosed was filled with mould up to the level of the top of the slabs, and this again was thickly planted with large shrubs. Jack walked all round this affair, peering keenly into the dense leafy screen. It was so thick that nothing could be seen of what was in the middle. Then he returned to the starting-point—that opposite to the place where he had picked up the diamond. He caught hold of the branches and pulled them apart. Then he uttered a low whistle. ’Come and look at this!’ he cried. The other two ran up to the place and peered in. There, upon the loose mould, could be seen a footprint, and a little beyond it another. Jack pointed to one of the bas-relief figures on the slab. It was in a kneeling position, and the head formed a convenient step to any one wishing to mount to the top of the slab. ’Do you see?’ he cried. ’This has been used as a step! You place a foot on it—thus, take hold of these branches—so, pull them apart—so, and you can spring up and through quite easily. Then the branches close up after you and hide all trace. But the last one who passed this way was in a great hurry. He was in such haste to get through that he snapped off a twig—here it is—and another twig caught against his breast, and tore off a little diamond, and cast it on to the floor where I found it.’ While talking, Jack had suited actions to words, and shown, by practical illustration, how easily what he had suggested might happen. ’Where, then, is that person now, do you suppose?’ asked Gerald, in a low tone. ’Hiding in the middle of those bushes?’ Jack shook his head. ’I should say not,’ he replied. ’I should say there must be a secret passage leading to this curious place, and that those bushes conceal the entrance to it. However, that’s a question we’ll soon put to the test. I ’m going in to see what’s in the middle. You fellows come after me!’ *CHAPTER XXI.* *A SECRET TREASURE-HOUSE.*