dors which surrounded the main spiral runway. From these circular corridors ran the numerous horizontal tunnels leading to the workings at each level. Shafts for ventilation and emergency exit pierced these tunnels at varying distances, running from the surface to the lowest levels of the quarry.
At almost every level a few slaves turned off into these lateral tunnels which were well lighted, though not quite as brilliantly as the spiral. Shortly after they had commenced the descent, Tarzan, accustomed from infancy to keen observation, had taken note of the numbers of tunnel entrances they passed, but he could only conjecture at the difference in the depths of the levels into which they opened. A rough guess placed them at fifteen feet, but before they reached the thirty-sixth, into which they turned, Tarzan felt that there must be an error in his calculations, for he was sure that they could not be five hundred and forty feet below the earth’s surface with open flames and no forced ventilation.
The horizontal corridor they now entered after leaving the spiral curved sharply to the right and then back to the left. Shortly afterward it crossed a wide, circular corridor in which were both laden and unladen slaves, beyond which were two lines, those laden with rock moving back in the direction from which Tarzan had come, while others, bearing lumber moved in the same
