But there may be too much of a good thing; the rocks may come in faster than the river mill can take care of them. Then the river bottom becomes so completely paved over that the channel stops wearing down at all, to speak of, and the river remains at the same level until the rains and the wind and other workers have worn the banks down and lessened the incline. Then, with fewer and fewer fresh stones tumbling in, the river gets a chance to catch up with its work. It is this ground-up rock stuff of the mountain river mills, made by the grinding of the running streams all the way down, that has helped form the rich bottom-lands of the Mississippi Valley. For uncounted ages, the water of the Mississippi and its tributaries have been at work, and by the time you get down into southern Louisiana you come to the delta where this rich soil has been piled up for more than 1,000 feet above the bottom of the old Mediterranean Sea, that used to reach north and south across the country. You remember the lines, don't you: "Little drops of water, little grains of sand Make the mighty ocean and the pleasant land." Well, this is how they do it; all this that I've been telling you. [Illustration: _Courtesy of the Scientific American._ THOUSANDS OF FARMS POURED INTO THE GULF The Father of Waters is a good farmer in some respects but needs training in others. The Mississippi's floods, like those of Father Nile, enrich the bottom lands, but the river is apt to break all bounds and do a lot of damage. Moreover, every year it carries away thousands of acres of good soil and pours it into the Gulf. How to teach the Mississippi to work in harness, as the Nile has been taught to do in recent years, is one of the problems which will require all of Uncle Sam's ingenuity and skill to solve. A good deal of the yearly waste could be prevented, however, by the various means employed by good farmers.] III. HOW THE RIVERS ACT AS BANKERS FOR THE FARMERS AND THE SEA We speak of river banks and the kind of banks that handle those promissory notes our arithmetics tell about as if they were entirely different; and so they are, I suppose, if one just looks at the surface of the thing. But if we dig into the subject a little we shall see that they are much alike in the fact that one of the principal businesses of both kinds of banks is to make loans at interest. Men's banks loan money, to be sure, while the river banks loan pebbles, but if it were not for these pebble loans there would be a mighty sight less money for the banks to loan, or the farmer to borrow; and the way both banks do business ought to be a good lesson to certain farmers I know, who seem to think they can always be cashing checks on their banks--the farm lands--by hauling away the crops without ever putting anything back. [Illustration: WHERE THE RIVERS ACT AS BANKERS