He had now been below the Curtain--below, that is, the northern ellipse of the Curtain, for it was known to enclose the Atlantic and Pacific coasts as well--for thirty minutes, boring steadily south despite the zigzag pattern of his exploration, and the character of the terrain was changing, not less mountainous but with some indications of a seasonal variation in the snow pack, for oftener now the bare rock precipices and peaks showed through, and beyond the upraised spine of the Rockies, toward the distant shimmering deep blue of the Pacific, the snow itself had taken on a stippled appearance--immense forests, O'Hara concluded, blanketed but shaping the white countours upon them. And farther still, merging into the rim of the ocean's curve, lay a varying band of dark brown and black and vivid green, presumably a thickly forested shore, completely free of snow. O'Hara made a quick calculation based on his known altitude and an approximation of the distance to the horizon. The result astonished him. The forest belt extended inland for three hundred miles. Yet the flight was becoming monotonous to the point of lulling him. The letdown that followed his discovery that the upper reaches of the continent were so remarkably similar to Siberia had increased, and with the passage of time he felt his eyelids inexorably closing. There was nothing to it. The dreaded continent was a fable made mysterious only by distorted memories of its history. It was, after all, a hoax--an empty shell, and he was penetrating deep-- His next thought jerked him erect in the cockpit of his craft. Suppose it was in fact an empty shell? Suppose there was nothing in this immensity behind the Curtain, the land which had been his fathers' fathers, but these ice-choked rivers and frozen tundras and forests and these tortured and interlocking mountain chains? Suppose it was dead--without life? And it well might be. O'Hara himself had been exposed steadily now for the better part of an hour to a degree of contamination that the International Patrol considered beyond dangerous, and in his flights to the east and west he had plunged through belts exceeding .300 milliroentgens an hour. Was it not probably that these Americans in establishing their Atomic Curtain had simultaneously contaminated their two continents beyond endurance? The suicide of a race? In an instant of panic, O'Hara swung in a tight arc to the north. He had, he felt, only the one chance to escape--a dash at maximum speed back to the Curtain and through it. But, as instantly, he discarded that. Whatever it was that had got him through the Curtain in the first place could not be expected to work twice. He was convinced that it had been a kind of providential accident, something to do with that splitting blast of electrical power in the thunderhead, and he was here, within this Western Hemisphere, inescapably cut off.