Dick went on. In some parts the tunnel was almost impassable with earth and rocks that had fallen in. Step as cautiously as he might, every now and then the rattle of loose earth displaced by his movements caused a cold shiver to run down his back. What if there should be a fall behind him which would cut off his retreat to the cave? The tunnel ought to lead to an opening to the air above, but the way might be blocked, and the possibility of being entombed was daunting. But having come so far Dick was unwilling to give in. The peril might be purely imaginary. Plucking up his courage, he hastened his steps, and after a few minutes came to an enlargement of the tunnel. To his left a second gallery ran downward at a sharp angle with that in which he was; no doubt this also led to some point of the shore. Still advancing, he saw, with some surprise, that the passage was strutted in places, and much freer from obstructions than the portion he had already traversed. About a hundred yards beyond the transverse gallery, however, his progress was suddenly checked: the whole width of the tunnel was filled with a mass of rocks, stones, and loose earth. A few seconds’ examination sufficed to show the impossibility of proceeding farther in this direction; accordingly he retraced his steps and, a few yards away, came to another passage, to find, however, after twenty or thirty paces, that he was again brought to a stop. This time the obstruction was of a different nature. It was a rough door made of stout wooden beams, closed with a heavy bar resting in sockets. He lifted the bar and pulled the creaking door, which came towards him for an inch or two, and then stuck. To open it fully he had to remove from the floor a number of planks and beams, which appeared to be the parts of a broken windlass. Having got the door open and passed through, he found himself in a square chamber that smelt very damp and close, though, on looking upwards, he could see no roof. He concluded that he was at the bottom of a deep shaft. But it had not the look of a mine shaft, which, so far as Dick’s experience went, was always timbered. The walls here were cased with stone, moss-grown and damp.