Treading water for a moment he looked round for a place where the bank would be easy to scale. A spot quickly caught his eye, and towards this he was about to strike out, when a strange phenomenon startled him. _The bank appeared to be rising slowly out of the water!_ He could scarcely believe the evidence of his own eyes. The sides of the pond had not been more than eight feet in height when first he struck the water; of that he was perfectly sure; yet now, at the very lowest point, they were twelve feet, and seemed to be getting higher each moment. Was he the victim of some delusion? He rubbed his eyes, he pinched his arm to assure himself that he was not dreaming. Then, with startling suddenness the truth came to him. _The water of the pool was slowly sinking!_ CHAPTER XIX. THE FIRE GULF. THE shock of this discovery aroused him to action. Swimming to the spot he had picked out, he commenced once more to scale the bank. Eight feet he climbed; his goal was almost within reach, when, without warning, the whole face of the bank to which he was clinging gave way, and he plunged down again into the water, the earth rattling over him as he fell. He was somewhat alarmed when he rose again. The water was still steadily sinking, and he was no nearer escape than at his first attempt. Indeed, he was further from his object, for the lower the water sank the higher he would have to climb. Escape from the pool did not appear so easy as it had done some time before. Once more he made an attempt to scale the side, but with no better luck than before. After this he contented himself with treading water for a time, reserving his energies for a final effort. How much lower was the water going to sink? he wondered. It was twenty feet below the level of the valley now, and its motion had not yet ceased. He thought nothing of the strangeness of the phenomenon. His mind was centred upon escaping from his alarming predicament. Suddenly the water began to swirl and eddy. He was expecting each instant to be sucked down into some dark hole, when, with a dull roar, that seemed to come from the very bowels of the earth, the water foamed upward. Five minutes later it was as Wilson had found it, a silent, somewhat ghostly-looking pool, scarce a ripple remaining to tell of its recent movement. Now or never! thought the engineer. Exerting all his remaining strength, he made a desperate effort to ascend the slippery bank. Again and again he tried, but ever with the same result. Failure, heartbreaking failure! And upon it all, while he rested from his last attempt, the water began to sink again. At that his courage failed. He had almost decided to let himself sink beneath the surface, and so end the apparently hopeless struggle, when the sound of voices fell upon his ears--the voices of his friends.