Another curious thing is how the river mills help themselves to new millstones when they need them. If a river hasn't enough for its work, it has a way of drawing on its banks for more. Whenever the stones in its bed get scarce, so that it can make comparatively little new soil--having so few stones to grind together--it proceeds to dig its own bed deeper, since this bed is no longer protected by a rock pavement in the bottom. This, of course, deepens its channel, and so adds to the steepness of the slope of its banks. Then, owing to this increase in the incline of the slope, more rocks tumble in, and the "milling business"

picks up again.

THE GOVERNOR IN THE RIVER MILL

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.

[Ill.u.s.tration: _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 princ.i.p.al 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.

[Ill.u.s.tration: WHERE THE RIVERS ACT AS BANKERS

Here is a fine piece of bottom land, one of those "banks" where the rivers keep "checking accounts" for the farmers and the sea; using pebbles for currency, as explained in this chapter.]

HOW THE RIVERS PLACE PEBBLES ON DEPOSIT

The rivers make loans to the soil by depositing pebbles in the broad bottom-lands along their banks, and then draw interest by carrying along to other lands, from time to time, some of the fine rich soil these pebbles help make by their decay. And the river does this in regular banking style, "checking out" the pebbles from time to time, and then depositing other pebbles in their places. Take the banks and bottom-lands of the Mississippi River, for example. It has been estimated that it requires about 40,000 years for a pebble to make the journey to the Gulf from the mountains of a tributary stream where it was first broken from the rock as a sharp fragment.

The first part of the journey in the mountains is over steep down grades, and so is comparatively fast, but as the river gets farther from the mountains, the slope of its bed becomes less and less, the onward movement is slower and slower, and more of the pebbles stop to rest. In times of flood they are carried far away from the regular channel and spread over the wide flood-plain of the river. Then, as the flood goes down, they are left buried there under a coating of mud. So buried, they decay and enrich the soil. Then the next flood that comes along sweeps the pebbles with it--checks them out of the bank--but at the same time carries away not only some of the soil richness which these pebbles helped to make but the soil material made by the decay of the vegetation these pebbles thus helped to grow, such as the roots and blades of wheat and corn and stubble and chaff left in the fields. That's the interest on the loan. Then, when the flood subsides, the pebbles are again deposited farther along in the river's course, but meanwhile the same flood has brought fresh deposits of pebbles from up-stream, and these are left in place of those taken away.

RIVER BANKING AND HUMAN CIVILIZATION

This banking business has been going on for ages and is a very important part of the history of civilization. Here and there along the sides of the older and larger river valleys are found the remains of ancient plains. These plains are now, many of them, quite a distance above the level of the stream. This means that they were at one time the bottom-lands of that same stream, but the stream, as it dug deeper and deeper into its bed, grew narrower, and so abandoned its old flood-plains. As savage man gradually settled down and took to farming, he found these bottom-lands, with their rich, mellow soil, just the thing for his crooked-sticks and stone hoes--the only kinds of ploughs and hoes there were in those days. With such crude farming tools he couldn't have managed to scratch a living on any other kind of soil.

When the river floods came along, all these crooked-stick farmers had to do was to keep out of the way until the floods went down, and there were their fields all fertilized for them, as good as new, and they could go on for thousands of years working the same fields without ever bothering their heads as to whether they needed any lime or potash or nitrogen, or anything; for they didn't. The river floods attended to all that.

[Ill.u.s.tration: FATHER NILE AND THE MAKING OF EGYPT

"Egypt," said Herodotus, "is the gift of the Nile"; and it is true so far as her fertile lands are concerned. The ancients attributed the annual floods to the G.o.d of the Nile, as shown in that statue of Father Nile in the Vatican. Below is a threshing scene in Egypt painted by Gerome. The last picture, from a carving in the tomb of an Egyptian n.o.ble, shows how they ploughed and sowed in the Pyramid age.]

So, in course of time, civilizations such as those of Egypt and India and Persia grew up, and in further course of time these civilizations spread into Europe, and finally to the New World.

HOW RIVER BANKS GO BANKRUPT

Now all this is very well, this leaving it to Nature to fertilize the fields, where everything is just right for it, as it is along the Nile, but in most lands it won't do it all. The trouble is that, in raising the grain foods, the ground must be kept free of gra.s.s and weeds, and well ploughed during the rainy season. But the same rains that water the fields wash more or less good soil into the streams; much more than Nature alone can put back. For instance, down in Italy where, if the old forests were still there, the rains wouldn't wash away more than a foot of soil in 5,000 years, this soil is being carried into the Po, and by the Po emptied into the sea so fast--a foot in less than 1,000 years--that if you visit Italy to-day, say, and then go back in ten years, you'll see bare rocks on many a hillside that is now clothed in green. On such rocks the soil is already thin, and in ten years more it is all gone; all washed away! This thing is going on all around the sh.o.r.es of the Mediterranean. You are constantly coming on sections of country that used to be covered with great forests and prosperous farming communities where the soil has vanished, and many stretches of barren, rocky land where hardly a weed can find a foothold.

[Ill.u.s.tration: WHAT HAPPENS TO THE LAND WHEN THE TREES ARE GONE

Could anything be more desolate? You can see from this example how vital to our national life is the forest conservation work of our government.

Trees, by the network of their roots, keep the soil from washing away, retain moisture by their shade, and absorb the water of the rains and the melting snows so that it reaches the rivers and the creeks gradually. But when the trees are gone the water, unchecked, rushes down the slopes in floods, washing away the precious soil and leaving them as barren as a desert.]

"But, what are you going to do about it?" you say. "You can't change the slope of the hills, can you? And the farmer has _got_ to plough his land--you just said so yourself."

Yes, he's got to plough his land, to be sure; but so has he got to have pasture for his live stock. If he hasn't any live stock, that just shows what kind of a farmer he is. Every farmer ought to have live stock. Corn always brings a great deal more when it goes to market "on four feet,"

as the saying is; and, besides, the live stock give back to the fields, in the shape of manure, a large part of what they eat. Now, if you have live stock you must have pasture, and all land with a slope of more than one foot in thirty should be used partly for pasture and partly to grow wood for the kitchen stove, and hickory-nuts and walnuts for winter firesides. Although the land slopes, the mat made by the gra.s.s roots will keep it from washing away.

"But suppose you lived where there wasn't any land to speak of that didn't tip up; in New England, say--what would you do then?"

Leave the upper part of the slopes in the woods. Then the water that carries off the soil will not run entirely away, as it does in ploughed fields, but will creep down slowly, and, charged with the decay of the woods, help fertilize the lower lands and change the rocks beneath them into soil--the acids from the decaying vegetable matter eating into them.

"But still," you say, "there are farm lands that must be ploughed even if they do wash away; they're all the land a man has, sometimes. What then?"

Plough deep. Then the soil soaks up more of the rain and lets the water pa.s.s away in clear springs. This not only saves soil but, as we have just said, helps to decompose the subsoil and the bed rock.

Then there's another thing that good farmers do in such cases. They plough ditches along the hillside leading by a gentle slope to the natural watercourses; so the water of the rains, instead of going down the hills with a rush, and going faster the farther it runs--like a boy on a toboggan--is caught and checked in these sloping ditches, and much of the soil it contains deposited before it reaches the streams.

[Ill.u.s.tration: HOW THE FRENCH PROTECT THEIR HILLSIDE FARMS

This is how the French peasant keeps the mountain torrents from carrying off his precious soil.]

The best way of all, of course, is to build terraces, as they do in the thickly settled parts of Europe. But this is only profitable for the more valuable crops and not for ordinary grains.

SUCH SPENDTHRIFTS OF G.o.d'S GOOD SOIL!

My, but it's a shame the way we've wasted soil in this country. What spendthrifts! To start with--when the country was first settled--there seemed no end to the fine land, and every one could have a good farm for the asking. All he had to do was to make his wants known to Uncle Sam and then go out and help himself. What happened then? Why, what always happens? Easy come, easy go. These pioneer farmers worked their farms for all there was in them; didn't bother, many of them, even to haul the barn manure into the fields. Then when the old farm was exhausted they moved off to new lands and did the same thing over again.

[Ill.u.s.tration: A HOME IN THE DESERT

Doesn't look much like a home in the desert, does it? But it is--a lovely home in what the old geographies called "The Great American Desert." In the Sahara oases are few and far between, but modern irrigation engineering makes oases to order--thousands and thousands of acres of them!]

They ploughed on steep hillsides; they allowed gulches to form, as they will quickly do on sloping ploughed land, if you don't watch out; they cut away the timber. It's easy in a hill country like the eastern part of the United States to have all the good top-soil washed away in twenty years after the forests have been destroyed; the good soil that it probably took 2,000 years to make.

Doctor Shaler[8] estimated that in the States south of the Ohio and the James Rivers more than 8,000 square miles of originally fertile land had, by this shiftless and thoughtless way of doing things, been put into such a state that it wouldn't grow anything; and over 1,500 square miles of this, actually worn down to the subsoil, and even to the bed rock, so that it may never be profitable to farm again--at least not in our time--no matter what they do!

[8] "Outlines of Earth's History."

I knew a farmer with a small son to whom he intended to leave the farm when he grew up, who did things like that for twenty years. By the time the little boy was old enough to vote, there was no farm to leave; all the good part of it was gone.

Serious thing for that little boy, wasn't it?