“Well, most rivers carry very little mud in their water, and that little goes to make the bar at the mouth. The Mississippi carries so much mud that its bars become land, and the river cuts a channel through them, carrying its mud still farther into the sea. Then again, the Mississippi has floods every year or twice a year, and in some years three times, such as most rivers never have. This is because it carries in a single channel the water from twenty-eight states and a territory, as we saw on the map one day up the river. Now as soon as the river mud forms a bar that shows above water, vegetation begins to grow on it. When the next flood comes, it covers the new-made land and builds it higher by depositing a great deal more mud on top of it and among the vegetation, which, by checking the current at the bottom, helps the mud to lodge there. In that way, all the lowlands for hundreds of miles along this river were created. It took hundreds of thousands of years--perhaps millions of years--to do it, but it was done.” Ed did not give this long explanation all in one speech. He was interrupted many times by Phil’s call of all hands to the sweeps, when rowing was necessary, and by other matters of duty, which it has not been necessary to detail here. Whenever it was possible to land the boat for the night, the boys did so, and when no banks were in sight where a mooring could be made, they sought for some bend or pocket reasonably free from the more dangerous kinds of drift, and came to anchor for safety during the hours of darkness. Navigation was difficult and perilous now even in daytime when they could make out the course of the river by sight and keep away from treacherous shore currents, for the drift was very heavy. By night it was doubly dangerous. Even in the daytime Phil kept the entire crew on deck at all times except when one of them went below to prepare food. Their meals were eaten on deck with a broad plank for table, even when it rained heavily, as it very often did. They slept on deck, too, under a rude shelter made of the tarpaulin. All this Phil regarded as necessary under the circumstances. Even when tied up to the trees or anchored in the snuggest cove to be found, it was sometimes necessary to jump into skiffs and “fend off” great threatening masses of drift. To this duty the calls were very frequent indeed. Poor Phil got scarcely any sleep at all during these trying days and nights. The sense of responsibility was so strong upon him that he scarcely dared relax his personal watchfulness for a moment. But under the urgent pleadings of his comrades he would now and then leave another on duty in his place and throw himself down for a nap. He did this only when the conditions seemed most favorable, and usually even then he was up again within the half hour.