There was something sinister in the strange silence that hung over them. One was of queer construction--a windowless, square, high box of galvanized iron. The other was obviously a dwelling place. Carefully Phil sneaked up to the latter. Then, rifle ready, he pushed its door open and sent a beam of light stabbing through the darkness of the interior. There was no one there. Only two bunks, a table, chair, a pail of water and some cooking utensils met his view. He crept out toward the other building. Come close, Phil found that a dun-colored canvas had been thrown over the top of it, making an adequate camouflage in daytime. The place was about twenty feet high. He prowled around the metal walls and discovered a rickety door. Again, gun ready, he flung it open. The beam from his flash speared a path through the blackness--and he gasped at sight of what stood revealed. There, inside, was a long, bullet-like tube of metal, the pointed end upper-most, and the bottom, which was flat, toward the ground. It was held in a wooden cradle, and was slanted at the floor. In the bottom were holes of two shapes--rocket tubes and disintegrating projectors. It was another earth-borer. * * * * * Phil stood frozen with surprise before this totally unlooked-for machine. He could easily have been overcome, had the owner been in the building, for he had forgotten everything but what his eyes were staring at. He started slowly around the borer, found a long narrow door slightly ajar, and stepped inside. This borer, like Guinness's, had a double shell, and much the same instruments, though the whole job was simpler and cruder. A small instrument board contained inclination, temperature, depth and air-purity indicators, and narrow tubes led to the air rectifiers. But what kept Holmes' attention were the wires running from the magneto to the mixing chambers of the disintegrating tubes. "The fools!" he exclaimed, "--they didn't know how to wire the thing! Or else," he added after a moment, "didn't get around to doing it." He noticed that the projectile's interior contained no gyroscope: though, he thought, none would be needed, for the machine, being long and narrow, could not change keel while in the ground. Here he was reminded of something. Stepping outside, he estimated the angle the borer made with the dirt floor. Twenty degrees. "And pointed southwest!" he exclaimed aloud. "This borer would come close to meeting the professor's, four miles under our camp!" * * * * * At once he knew what he would do. First he went back to the other shack and got the pail of water he had noticed, and took this out where the Mexican lay outstretched. He bathed the man's face and the still slightly bleeding bullet wound in his shoulder.