Heavy details were made from the troops, the working parties were carefully selected, and on the 30th of April the work was begun. From the north bank a wing-dam was constructed of large trees, the butts tied by cross logs, the tops laid towards the current, covered with brush, and weighted, to keep them in place, with stone and brick obtained by tearing down the buildings in the neighborhood. On the south bank, where large trees were scarce, a crib was made of logs and timbers filled in with stone and with bricks and heavy pieces of machinery taken from the neighboring sugar-houses and cotton-gins. When this was done there remained an open space of about one hundred and fifty feet between the wings, through which the rising waters poured with great velocity. This gap was nearly closed by sinking across it four of the large Mississippi coal-barges belonging to the navy. When on the 8th of May all was thus complete, the water was found to have risen five feet four and a half inches at the upper fall, giving a measured depth there of eight feet eight and one half inches. Three of the light-draught gunboats, _Osage, Neosho_, and _Fort Hindman_, which had steam up, took prompt advantage of the rise to pass the upper fall, and soon lay in safety in the pool formed by the dam; yet for some reason the other boats of the fleet were not ready, and thus in the very hour when safety was apparently within their reach, suddenly they were once more exposed to a danger even greater than before. Early on the morning of the 9th the tremendous pressure of pent-up waters surging against the dam drove out two of the barges, making a gap sixty-six feet wide, and swung them furiously against the rocks below. Through the gap the river rushed in a roaring torrent. At sight and sound of this, the Admiral at once mounted a horse, galloped to the upper fall, and called out to the _Lexington_ to run the rapids. Instantly the _Lexington_ was under way, and as, with a full head of steam she made the plunge, every man in the army and the fleet held his breath in the terrible silence of suspense. For a moment she seemed lost as she reeled and almost disappeared in the foam and surge, but only to be greeted with a mighty cheer, such as brave men give to courage and good fortune, when she was seen to ride in safety below. The _Osage_, the _Neosho_, and the _Fort Hindman_ promptly followed her down the chute, but the other six gunboats and the two tugs were still imprisoned above by the sudden sinking of the swift rushing waters; the jaws of danger, for an instant relaxed, had once more shut tightly on the prey. Doubt and gloom took the place of exultation. As for the army, hard as had been the work demanded of it, still greater exertions were before it, nor was their result by any means certain, for the volume of the river was daily diminishing, and there would be no more rise that year.