About this time Gray began to suspect that the tide was bearing them onward at a remarkable rate. In the somber depths of the cleft or cañon it was difficult to discern stationary objects clearly enough to obtain a means of estimating the pace of the stream. But the rapid dying down of the hubbub among the savages gave him cause to think. He asked Suarez to cease pulling. The canoes behind came crowding in on the more solid boat, and an oar held out until it encountered some invisible branch was rudely swept aside. In a word, they were being impelled towards an unknown destination with the silence and gathering speed of a mill-race. An expert engineer, though his work may have little to do with sea or river, cannot fail to accumulate a store of theoretical knowledge as to the properties and limitations of water in motion. Gray knew that the quickened impulse of the stream arose from the tidal force exerted in a channel which gradually lessened its width. The boat was traveling at sea level. Therefore, there could be neither rapids nor cataract in front; but the steady rush of the current, now plainly audible, could not be accounted for simply by the effort of the tide to gain a passage through a mere by-way, as the boat was now nearly half a mile from the estuary, and the velocity of the current was increasing each moment. “We must endeavor to reach the bank and hold on to the branches of a tree,” he shouted in Spanish. “Down with your heads until the boat strikes, and then try to lay hold of something.” There was no time for explanation. He seized an oar; a powerful stroke swung the boat’s nose round. By chance, he used the starboard oar. All unknowing he spun a coin for life or death, and life won. They crashed through some drooping foliage and ran into a crumbling bank. Gray unshipped the oar and jammed it straight down. It stuck between stones at a depth of three feet, and the life-boat was held fast for the time. The canoes hurtled against each other, but were swept aside instantly. When the noise ceased, they plainly heard the swirl of the water. In their new environment, it had the uncanny and sinister hiss of some monstrous snake. “Everybody happy?” Gray demanded coolly. “I am clinging to a tree trunk,” answered Elsie. “Bully for you. Make fast with a piece of rope. But be careful to provide a slip-knot, in case we have to sheer off in a hurry. Can you manage that?” “Quite well.” Elsie was fully aware that the leadership of the expedition had gone from her. She was not sorry; it was in strong hands. Suarez, too, secured a stout branch, and passed a rope around it. “Now, silence! and listen!” said Gray.