Suddenly a crashing report, so loud that it resembled the simultaneous discharge of a whole army of rifles, smote upon their ears; and then, as they stood in a trance of breathless expectation, wondering what was about to happen, an immense section of the icy cliff was seen to be in motion. Slowly at first, but with ever-increasing rapidity, it slid downward into the water, with a continuous roaring reverberating crash, to which even the awful pealing of thunder was as nothing, until in a wild turmoil of madly leaping and foaming surges it disappeared entirely below the water. The sea rushed irresistibly after it from all sides, pouring like a foaming cataract into the hollow watery basin it had left, and dragging the _Flying Fish_ helplessly toward the yawning vortex. Then the inward rush suddenly ceased; a gleaming white crest of ice reappeared above the foam, and with a mighty upward rush and a resounding roar the gigantic submerged mass once more upreared itself above the again maddened waters, swaying heavily to and fro, whilst a thousand gleaming torrents poured down its sparkling sides. And, as a fitting _finale_ to the thrilling spectacle, a huge wall of water suddenly heaped itself up about the rocking mass and began to rush rapidly outward in an ever-widening circle, its towering crest surmounted by a roaring curling fringe of snow-white foam. Increasing in height and in speed as it advanced, it rapidly attained an altitude of fully sixty feet, bearing down upon the _Flying Fish_ so menacingly that, for a few seconds, the party in the pilot-house stood paralysed with consternation, expecting nothing less than that they would be helplessly overwhelmed. The first to recover his presence of mind was Mildmay, who, springing to the rods which controlled the air-valves, pressed them powerfully down, throwing them all wide open and at once ejecting from the hull both the water and the compressed air, and causing the ship to rise until she floated lightly as an air-bubble on the water. He then injected a dense body of vapour into the air and water chambers, completing the vacuum; and the ship rose into the air just in time to avoid the gigantic surge, which went hissing and roaring close beneath them with a power and fury which fully revealed to them the extent of the disturbance from which they had so narrowly escaped. Other surges followed in quick rotation; but each was less formidable than its predecessor, and in another ten minutes the surface had once more subsided into a state of comparative calm. As the _Flying Fish_ once more settled down upon the water and the air- pump was set going, the professor turned to his companions and remarked: "We have especial reason to congratulate ourselves and each other, gentlemen, for we have to-day not only looked upon the magnificent Humboldt Glacier under most highly favourable conditions, but we have been also permitted to witness that even rarer sight, _the birth of an iceberg_!"