The Mississippi River is a great antimonopolist. As more and more railways have been built it has been less and less used. And yet, because it drains almost every corner of a valley which comprises over one third of the whole United States, it affords means of transportation to an immense area; and since it cannot be controlled by any one company or group of companies, its freight rates can hardly be arbitrarily fixed. Still, so long as there are impediments to its free navigation in the shape of floods and bars, it cannot be depended on for shipping, and the magnificent opportunities it should offer to commerce are lessened. The vastest river system in the world, it shows in its various parts great contrasts. One large tributary flowing from the Alleghanies, one from the Rockies, one from the north, others from the southwestern plains, are each able to contribute their various products of grain, lumber, cattle, cotton, fruits, and so on. Some branches freeze every winter; others never do. Some are clear, others silt-bearing. From about Cairo it flows southward through the greater delta, or land built up by its own action in ages past, and in all this part of its course both banks and bottom are of yielding alluvion. For some hundreds of miles "the crookedest of great rivers," it varies frequently in width and velocity and is full of shoals; then for hundreds more, though uniform in width, it often rises higher than its shores, and is confined in artificial levees, which it continually breaks down. Finally, below New Orleans, growing more sluggish, and dividing into several mouths, or "passes," it wanders through tracts of waste marsh-lands into the gulf, which it colors brown for miles around. Blocking the end of each shallow mouth there was formerly a sand-bar; and these obstructions to navigation were the despair of the river commerce, and no less the despair of the government in its attempts to remove them.