The white man sat for a long time buried in thought. Time and again his eyes examined every detail of the formation of the fissure within the range of his vision. Again and again they returned to the huge fragment upon which they sat, which was securely wedged between the fissure's sides. With this out of the way he felt that they could make unimpeded progress to the next terrace, but he knew that nothing short of a charge of dynamite could budge the heavy granite slab. Directly behind it were loose fragments of various sizes, and as his eyes returned to them once again he was struck with the possibility that they suggested. "Come, Gabula," he said. "Help me throw out some of these rocks. This seems to be our only possible hope of escaping from the trap that I have got us into." "Yes, Bwana," replied Gabula, and fell to work beside von Harben, though he could not understand why they should be picking up these stones, some of which were very heavy, and pushing them out over the edge of the flat fragment that clogged the fissure. He heard them crash heavily where they struck the rocks below and this interested and fascinated him to such an extent that he worked feverishly to loosen the larger blocks of stone for the added pleasure he derived from hearing the loud noise that they made when they struck. "It begins to look," said von Harben, after a few minutes, "as though we may be going to succeed, unless by removing these rocks here we cause some of those above to slide down and thus loosen the whole mass above us--in which event, Gabula, the mystery of The Lost Tribe will cease to interest us longer." "Yes, Bwana," said Gabula, and lifting an unusually large rock he started to roll it toward the edge of the fissure. "Look! Look, Bwana!" he exclaimed, pointing at the place where the rock had lain. Von Harben looked and saw an opening about the size of a man's head extending into the fissure beneath them. "Thank Nsenene, the grasshopper, Gabula," cried the white man, "if that is the totem of your clan--for here indeed is a way to salvation." Hurriedly the two men set to work to enlarge the hole by throwing out other fragments that had long been wedged in together to close the fissure at this point, and as the fragments clattered down upon the rocks below, a tall, straight warrior standing in the bow of a dugout upon the marshy lake far below looked up and called the attention of his comrades. They could plainly hear the reverberations of the falling fragments as they struck the rocks at the foot of the fissure and, keen-eyed, they could see many of the larger pieces that von Harben and Gabula tossed downward. "The great wall is falling," said the black warrior. "A few pebbles," said another. "It is nothing." "Such things do not happen except after rains," said the first speaker. "It is thus that it is prophesied that the great wall will fall."