As they neared it, any possible doubt that it was in fact a pyramid vanished. Corroded by the action of salt water and covered with the incrustations of centuries, it nevertheless presented unmistakable evidence of human construction, rising in steps of massive masonry to a summit shadowy in the murk above. As Larry stood gazing upon that mighty proof that this submerged plateau had once stood forth proudly above the sea, he realized that he was a party to one of the most profound discoveries of the ages. What a furore this would make when he reported it back to his New York paper! But New York seemed remote indeed, now. Would they ever get back? What if anything went wrong with their pressure-suits--or if they should become lost? He glanced back uneasily, but there gleamed the reassuring lights of the _Nereid_, not a quarter of a mile away. Diane and her father were now rounding a corner of the pyramid and he followed them, his momentary twinge of anxiety gone. * * * * * For some moments, Professor Stevens prowled about without comment, examining the huge basal blocks of the structure and glancing up its sloping sides. "You see, I was right!" he declared at length. "This is not only a man-made edifice but a true pyramid, embodying the same architectural principles as the Mayan and Egyptian forms. We see before us the visible evidence of a sunken empire--the missing link between Atlantis and America." No comments greeted this profound announcement and the professor continued: "This structure appears to be similar in dimensions with that of the pyramid of Xochicalco, in Mexico, which in turn approximates that of the "Sacred Hill" of Atlantis, mentioned by Plato, and which was the prototype of both the Egyptian and Mayan forms. It was here the Antillians, as the Atlanteans had taught them to do, worshipped their grim gods and performed the human sacrifices they thought necessary to appease them. And it was here, too, if I am not mistaken, that--" Suddenly his vibratory discourse was broken into by a sharp signal from the submarine: "Pardon interruption! Hurry back! We are attacked!" At this, the trio stood rigid. "Captain Petersen! Captain Petersen!" Larry heard the professor call. "Speak up! Give details! What has happened?" But an ominous silence greeted the query. Another moment they stood there, thoroughly dismayed now. Then came the professor's swift command: "Follow me--quickly!" He was already in motion, retracing his steps as fast as his bulky suit would permit. But as he rounded the corner of the pyramid, they saw him pause, stand staring. And as they drew up, they in turn paused; stood staring, too. With sinking hearts, they saw that the _Nereid_ was gone. * * * * * Stunned by this disaster, they stood facing one another--three lone human beings, on the bottom of the Atlantic ocean, their sole means of salvation gone.