Tarzan selected a large boulder, many of which were strewn about the flat top of the mountain, and when the leaders of the party were about half way to the summit and the others were strung out below them, the ape-man pushed the rock over the edge of the cliff just above them. In its descent it just grazed Zveri, struck a protuberance beyond him, bounded over Colt's head, and carried two of Kitembo's warriors to death at the base of the escarpment.
The ascent stopped instantly. Several of the blacks who had accompanied the first expedition started a hasty retreat; and utter disorganization and rout faced the expedition, whose nerves had become more and more sensitive the nearer that they approached Opar.
"Stop the damn cowards!" shouted Zveri to Dorsky and Ivitch, who were bringing up the rear. "Who will volunteer to go over the top and investigate?"
"I'll go," said Romero.
"And I'll go with him," offered Colt.
"Who else?" demanded Zveri; but no one else volunteered, and already the Mexican and the American were climbing upward.
"Cover our advance with a few rifles," Colt shouted back to Zveri. "That ought to keep them away from the edge."
Zveri issued instructions to several of the askaris who had not joined in the retreat; and when their rifles commenced popping, it put new heart into those who had started to flee, and presently Dorsky and Ivitch had rallied the men and the ascent was resumed.
Perfectly well aware that he might not stop the advance single-handed, Tarzan had withdrawn quickly along the edge of the cliff to a spot where tumbled masses of granite offered concealment and where he knew that there existed a precipitous trail to the bottom of the cliff. Here he could remain and watch, or, if necessary, make a hasty retreat. He saw Romero and Colt reach the summit and immediately recognized the latter as the man he had seen in the base camp of the invaders. He had previously been impressed by the appearance of the young American, and now he acknowledged his unquestioned bravery and that of his companion in leading a party over the summit of the cliff in the face of an unknown danger.
Romero and Colt looked quickly about them, but there was no enemy in sight, and this word they passed back to the ascending company.