HOW THE RIVER MADE THE VALLEY.
The river has much other work to do besides turning water wheels.
The valley in which you live was made by the river. It did this by carrying away little by little the particles of rock and soil along its path. It has taken many years for the river to do the work. It has not finished yet.
Let us look at the river after a heavy rain. The stream is yellow and muddy. It has almost over flowed its banks. Logs are floating by. Near us a tree has tipped into the river. The water has torn away the soil that held its roots.
Where does the river get the mud which makes it so dirty? We will take our umbrellas and go out while it is raining to a little ravine. In summer there is no water here. Now the bottom of the ravine is covered with a muddy torrent. The torrent is hastening on to add its share to the river.
Upon the sides of the ravine the water is at work. The slopes are just covered with tiny rills. Each rill is as muddy as it can be.
The raindrops when they strike the ground pick up little particles of sand and clay. The clay makes them dirty, but they do not care. The sand they cannot carry easily and so they drag it along the ground. When many drops have united in a rill they are strong enough to carry bigger things. Watch closely and you will see what is happening. The rill is cutting a tiny channel upon the hillside. Many rills are doing the same thing, and if. you look about, you will see that the sides of the ravine are all furrowed in this way.
Thus the work of tearing down the land goes on. The torrent in the bottom of the ravine into which the rills are flowing is hastening on to the river. There it will get rid of its load of mud and
sand.
It may be that so many creeks full of muddy water will be more than the river can take care of. The river cannot overflow its banks and do much harm when shut in between the hills. But when it reaches the lowland where it is bordered by a broad valley or plain it may form a flood.
At such times the people in the lowlands are afraid of the river. It may spread over their rich farms. Then they will have to leave with their cattle and goods. Perhaps their houses will be washed away.
The river flows mute slowly when it spreads ? out. It cannot any longer carry all the mud and sand which the creeks and rills gave it. When the farmer comes back after the water has gone down he finds that it has left a layer of mud over everything. It is the mud brought by the river that makes the bottom lands so rich.
The river does not drop all of its load here. It carries much of the finer material into the lake or ocean into which it flows.
The river thus does work in carrying dirt from one place to another. It is washing down the hills and filling up the lowlands.
We have now seeei how much work the water can do in one storm. Do you wonder that it has done great things in thousands of years? It has cut canons so deep. that you can hardly see the bottoms of them. It has worn down great mountains higher than any which you have ever seen. It has left only little hills in the place of these great mountains.