"It is a chasm a mile deep," explained Barma Shah, "but only half that distance across. Nobody has ever gone there, because it is supposed to be impassable." He traced a dotted line on the longompa's chart. "It must lead to the Lost City of Chonsi. No wonder no one has ever found it! We'll start for there tomorrow."
They were off to an early start the next morning and soon were among scenes of grandeur that surpassed any so far encountered. Narrow valleys filled with odd, colorful flowers formed a contrast to the snow-topped peaks that loomed high above. Then, abruptly, the trail reached the brim of a deep, granite-walled canyon. Nearby was a cluster of trees indicated on the parchment map. A dotted line began from there, so the party moved into the grove. There they were halted by a big rock until the boys probed the underbrush around it and found stone steps leading downward.
Soon, the whole procession was following a dizzy trail chiseled in the canyon wall. Barma Shah had been right regarding its depth: it was at least a mile and perhaps more. The vast gulch followed a zigzag as shown on the map, and as they steadily descended, the brim of the gorge was totally lost from view, due to the narrowing of the walls.
Then, the zigzag sharpened, and on their own side of the gorge, they saw a fascinating sight. Through an opening in the granite poured what looked like a mammoth waterfall, except that it was utterly motionless. At the bottom, half a mile beneath, was a vast, glassy mass, pock-marked by thousands of huge stones.
"An icefall!" exclaimed Charles Keene. "A stream of water, frozen solid, pouring down to a glacier below!"
As he spoke, they saw a chunk of ice and rock drop from the brink and slide out along the graceful, frozen curve until it dropped straight down and struck the glacier. Then came a rising echo that reverberated through the gorge like a long roll of thunder. When the sound finally died away, Barma Shah said coolly:
"That is why they call it the Place of Living Thunder. People have heard that roar from the brink above, but we are the first to see what caused it—except for those who live in the valley."
Their course brought them to the huge icefall. This time Charles Keene and Barma Shah led the way together, followed by Hurdu and the Tibetan bearers, with Biff and the boys bringing up the rear. The path seemed a very safe one, being hewn in the solid rock. Granite steps took them upward to the overhanging curve of the giant icefall. Above that, a bridge of large steppingstones crossed the whitish flowing mass.
Biff, in the lead, leaped to the first stone and felt it quiver. He should have turned back, but instead, he tried to jump on to the next. The first stone suddenly went from under him, spilling Biff backward. Mike, who had reached the top of the steps, grabbed for Biff's hand and caught it with both of his own. Then Mike was swept off balance by the force of Biff's slide. Both would have gone skimming over the brink, except that Chuba and Kamuka, coming next, were in time to catch Mike's ankles and hold them.
They hadn't the strength to pull the pair back, and Biff, from his precarious position, realized why. That curving brink of perpetual ice was so smooth that it offered nothing in the way of a hold, not even the slightest amount of friction. Slowly, surely, the drag would bring all four along, unless someone's hold gave out.