"There is no need yet," replied Mark; "we have a tremendously long way to go yet." "Let there be silence," said Sir Edward sternly. "For aught we know, these men, if the grottoes do communicate, may be exploring on their own account, and sound runs curiously along these passages." Mark accepted the rebuke, and joined Dummy at once, the rest of the party followed, and at a word from Sir Edward, raised their pikes and advanced steadily, as if expecting at any moment to meet the foe. But many hours seemed to have elapsed, during which they had climbed, descended, squeezed through narrow upright cracks, and crawled, as the two lads had crawled before, ere they reached the limpid pool where their guides had rested and gone to sleep. Here, at a word from Mark, Sir Edward gave the word to halt for refreshment, while, in company with the two lads, he made a farther advance, and planted two men at intervals along the route they took, following the flow of the underground stream, whose musical gurgling grew very plain at times. The second man was posted a good two hundred yards beyond the first, and made no objection to being left in the dark, showing Dan Rugg's wisdom in selecting miners for the task in hand. Then, silently and with great caution, Dummy led on along a wild chasm of the same nature as others they had passed, and formed, evidently during some convulsion, the encrinite marble of which the walls were composed matching exactly, and merely requiring lateral pressure and the trickling of lime-charged water to become solid once again. About three hundred yards beyond the last sentinel the trio paused, and stood listening and gazing as far as they could across a rock chamber whose sides glittered with double prismatic crystals. But there was the water gurgling at the bottom of the deep crack along which they passed--nothing more; and they returned toward the pool, Sir Edward giving the men a word or two of caution, and then passing on to the others who were whispering to each other as they ate their food. It was too good an example not to be followed, and soon after, quite refreshed, Sir Edward gave the order for a fresh start, the way being doubly interesting now that it was all fresh ground to the guides. In addition, it became more difficult, for the formation began now to change, and instead of being a succession of narrow crack-like passages--in almost every variety of inclination between the horizontal and perpendicular, and rock grotto-like chambers of varying extent--the road began to fork and break up into vast halls, from which more than once they could hardly find an exit. But Dummy was invaluable, and there was a kind of triumph in his face when he pointed out how easy it was to go on if you listened for the trickling of the stream below.