"Think she'll do it before dark?" inquired Uncle Brian, glancing at the sun, now only about thirty degrees above the horizon. "Rather," replied Peter. "It will be quite light up here after the low-lying ground is in darkness. Once we're above the peaks I don't mind. It will be plain sailing after that." "If you're sure of it, well and good," rejoined Brian. "If not, we'd better make a landing while it is light." The youthful pilot shook his head. "Twelve hours saved is twelve hours gained," he said sagely. "I don't want to spend another night in Rioguayan territory if it can be avoided. She'll do it." Fifteen minutes later, a violent bump announced that the flying-boat had struck an air-pocket, a clear indication of the adverse conditions that awaited her above the snowy peaks of the Sierras. She dropped vertically for nearly a thousand feet in spite of the pilot's efforts to counteract the sudden loss of "lift". Then staggering blindly into the furthermost wall of the invisible air chasm, the flying-boat "stalled" and almost stood on her tail, until she picked up and Peter was able to bring her back to her normal trim. The next five minutes was a perfect nightmare. Above the snowy crags, now pink in the diffused rays of the setting sun, she sped, side-slipping, banking, and plunging, as if scorning the desperate efforts of the pilot to keep her up. Once she nose-dived, flattened out, and made straight for a sheer wall of rock that a few seconds previously she ought to have cleared with a thousand feet to spare. Vainly Peter put the vertical rudders hard over. It seemed as if a collision was inevitable and that the shattered debris of the flying-boat would fall headlong into the fathomless chasm, when a side gust of terrific force hurled her, like a leaf, crab-fashion, so that she just scraped clear with a few feet between her port wing-tips and the pitiless face of the peak. Then, propelled upwards by a freak air-current of irresistible strength, the flying-boat was hurled, like a sheet of paper up a tall chimney, between the perpendicular walls of a deep defile. So near did she scrape the summit of one of the twin peaks, that the rush of air dislodged a mass of snow, sending it thundering into the abyss, with a roar plainly audible within the supposedly sound-proof pilot's cabin. Suddenly the roseate snow peaks gave place to a void of intense darkness. The crossing of the Sierras was accomplished. Ahead lay miles of country, sloping towards the Caribbean Sea, with nothing higher than three thousand feet to be encountered--at least, so the map read. "We're over!" exclaimed Peter thankfully, as the flying-boat settled down to her normal even style of flight. "More by luck than by anything else," thought Uncle Brian, who felt bruised and shaken all over.