The ever-shifting condition of the river channel[14] caused the pilot to seek all available information as to its latest position. When other boats were met there was an eager swapping of notes, for it was a common practice in later years for pilots to assist each other by keeping notes of the condition of the river over which they passed.[15] The pilots thus came to know the river by heart from its mouth to the head of navigation. The extraordinary knowledge of its topography and nomenclature which Captain La Barge retained to the end of his life was almost incredible. There was not a bend or rapid, a bed of snags, or other feature in all of its twenty-six hundred miles that was not as familiar to him as the rooms of his own house. [Sidenote: THE FUEL PROBLEM.] The most serious problem with which the Missouri navigator had to deal was that of procuring fuel. Wood alone was used, and this was obtained from the growths on the banks of the river. Cottonwood was the main reliance, because of its greater abundance, but it was not a first-class firewood. If green, it was next to impossible to maintain steam with it except by the aid of rosin. It was often found impracticable to carry the boat from one established wooding place to another, and it was then necessary to gather drift logs, or anything else that could be found. Whenever a trading post was abandoned its palisades and buildings quickly found their way into the steamboat furnaces, to the great, though transient, delight of the crew. In the earlier years the fuel was cut by the crew itself as the boat proceeded on her voyage. But as the traffic became more regular, wood yards were established, either by the boat-owners or by others who cut wood for sale. The Indians themselves found the business a profitable one, and finally refused to let the whites cut wood at all. The sale of their wood thus became a source of considerable revenue to them. In later years, during the Sioux hostilities, the wooding of boats was a most perilous matter. Crews were attacked at the landings and only the most vigilant precaution prevented great loss of life at such times.[16] To reduce this danger as much as possible, Captain La Barge equipped one of his boats with a sawmill, and took along a yoke of oxen. When he had to have wood he swung out a large stage, drove the team ashore, and dragged several logs on board with the utmost speed. As soon as this was done the boat proceeded on her way and the crew then sawed up the wood. The “wooding” of a boat was an interesting performance. The moment the boat touched the bank for this purpose the mate called out “woodpile,” and every available man leaped ashore, loaded himself with wood, and hastened back to the boat. In an incredibly short time the work was done and the boat was again on her way. [Sidenote: STEAMBOAT HOURS.]