Just then Bart stopped short, for there were steps outside, and a gleam of light appeared beneath the heavy door. Voices were heard, and the rattle of a soldier's musket. "Changing guard," said Abel to himself; and he found himself wondering whether the sergeant and his men would enter the prison. To add to the risk of discovery, there was a shuffling sound on the left, and a clink of chains, as one man seemed to rise upon his elbow; and his movement roused another, who also clinked his chains in the darkness and growled out an imprecation. All this time Bart remained absolutely motionless, and Abel listened with the perspiration streaming from him in the intense heat. Then there was a hoarsely uttered command; the light faded away, the steps died out upon the ear; there was a clink or two of chains, and a heavy sigh from some restless sleeper, and once more in the black silence and stilling heat there was nothing to be heard but the loud trumpeting buzz of the mosquitoes. Softly, as some large cat, Bart resumed his crawling movement, after thrusting back his leg and touching Abel on the chest with his bare foot as a signal. The building was quite a hundred feet long by about eighteen wide, a mere gallery in shape, which had been lengthened from time to time as the number of convicts increased, and the men had about two-thirds of the distance to traverse before they could reach the end, and at their excessively slow rate of progress the time seemed interminable before, after several painful halts, caused by movements of their fellow-prisoners and dread of discovery, the final halt was made. "Now, then, what is it?" whispered Abel. The answer he received was a hand laid across his mouth, and his heart began to beat more wildly than ever, for Bart caught his hand, drew it toward him, and as it was yielded, directed the fingers downward to the stone level with the floor. Abel's heart gave another bound, for that stone was loose, and as he was pressed aside he heard a faint gritting, his companion's breath seemed to come more thickly, as if from exertion, and for the next hour--an hour that seemed like twelve--Abel lay, unable to help, but panting with anxiety, as the gritting noise went on, and he could mentally see that Bart was slowly drawing out rough pieces of badly-cemented stone--rough fragments really of coral and limestone from the nearest reef, of which the prison barrack was built. Three times over Abel had tried to help, but the firm pressure of his companion's hand forcing him back spoke volume, and he subsided into his position in the utter darkness, listening with his pulses throbbing and subsiding, as the gritting sound was made or the reverse.