Al and Wallace galloped off down river at once, accompanied by two cavalrymen of their late escort to bring back their horses. Leaving so hastily gave them time for only a glance at Fort Union, though they sincerely wished for an opportunity to examine it more closely, for it was an interesting, and in that wilderness land, even an imposing structure. Built in 1829 as the then most advanced trading post of the American Fur Company, it had become in later years the centre of the fur trade of a vast territory, extending from the Rocky Mountains to the British line. It was larger and more substantially built than any other trading fort in the American West, and those who had seen them declared that no post of the Hudson's Bay Company in the British Possessions compared with it. Its stockade was two hundred and forty by two hundred and twenty feet in size, built of massive timbers and flanked by two large stone bastions, well armed with cannon, while several of its numerous interior buildings were also of stone. George Catlin, the distinguished artist who travelled all over the New World in making up his great collection of paintings of the American Indians, had visited the fort in 1832; Maximilian, Prince of Neuwied, the distinguished Austrian naturalist, had been there in 1833; and in 1843 the equally famous American naturalist, John James Audubon, had made the post his headquarters for some time. But when Al and Wallace passed through it, the days of the old establishment were numbered; two years later it was to be dismantled, the new army post of Fort Buford, two miles below and nearly opposite the spot where the _Island City_ had sunk, taking its place as a military establishment. The boys had not ridden far across the bottom, which was partly timbered and partly open grass land, when they saw the wreck of the steamer, lying out beyond a shore bar, her smoke stacks and upper works protruding above the water. The _Belle Peoria_ was moored beside her and men could be seen working on both vessels. Al breathed a sigh of relief when he saw that they were not too late. Riding on across the bar, the boys were soon at the water's edge and about one hundred feet from the steamers. In answer to their shouts a small boat immediately put off from the _Belle Peoria_ and came over for them. It was with the regret of parting from an old friend that Al for the last time caressed the rough neck and soft nose of Cottontail, who had borne him so faithfully through many perils and privations. The little horse nuzzled Al's cheek affectionately, as if he realized that they were bidding each other good-bye; then, with a strong hand-clasp from each of the soldiers, the boys stepped into the yawl and were rowed to the _Belle Peoria_. It did not take long to explain to Captain Lamont their object in coming, and he seemed heartily glad of their company.