is its bed. In the lowest part of the bed the stream flows more rapidly and causes this part to do more work in cutting and carrying than any other part. This is the channel. The course is the direction which the stream takes. SOURCE RIVER ARKANSAS RIVER THE MISSISSIPPI RED RIVER SYSTEMTHE LARGEST IN NORTH AMERICA. the river system drains is a RIVER BASIN. All streams flow into other streams or bodies of water. The ocean finally receives the water of most of the rivers of the world. The place where any stream begins is its source. The place where a stream flows into another stream or body of water is its mouth. The land bordering the stream is called its banks. THE LARGEST RIVER OF EUROPE. The land over which a stream flows OHIO RIVER Find the source, mouth, and banks of the streams in the pictures. Find them, also the bed and channel, in the streams near your school. Trace the water-partings and the tributaries in the sketch of the Mississippi-system. A stream may be small, a merry, gurgling brook,-or it may be a large, broad, and peacefully flowing river; but at times during the year both the brook and the river may become raging torrents, sweeping away everything that comes in their pathway. Most streams have their sources high MOUTH. up among the hills and mountains For some distance many of them plunge down the hill or mountain side in waterfalls or rush rapidly over the rocky bed to lower levels. In their descent, especially after heavy rains or during the melting snows, they loosen great masses IT FLOWS THROUGH LOW LAND. of soil and rock, which are carried along by the rushing water. The larger rocks drop to the bed of the stream, the smaller ones are rolled and rubbed against each other and against the rocky bed as they are carried along, until they become pebbles, gravel, sand, clay, and not the force to carry as much material as in the upper part of its course. The heavier soil is dropped, the lighter soil is carried to its mouth. Here it is carried away and dropped to the lake or sea bottom if there is a current. If there is no current it is dropped at the A NARROW RIVER VALLEY HIGH UP IN THE ROCKY MOUNTAINS. other soil. As the stream reaches more level land it flows more slowly. It has Describe it. mouth of the stream, thus building out the land. Such a stream has a building mouth. A DRY REGION FOR MOST OF THE YEAR. The main river of a system not only cuts its own channel in the mountain side or in the plateau, but each tributary stream does exactly the same thing. Study all of the pictures. Trace the tributary basins. Describe each. All streams have a work to do in cutting down the highlands, wearing out the val leys, and in carrying and depositing mate The deposit is a delta. Find the deltas in the rial to build up the plain or to build out the pictures. seashore. Some rivers flow in the val leys be tween the mountain folds. Other riv ers must be older than the mountains themselves. banks and spread out like great lakes on the level land, submerging COPYRIGHT DETROIT PHOTO CO. everything in their way. This is a flood. The land covered at flood-time is a FLOOD-PLAIN. The water which covers the flood-plain is filled with fine soil or with sand. When the flood subsides and the stream returns to its banks, the flood-plain is covered with mud. For a long time the water stands upon the surface in ponds. The floods cause most flood-plains to have a very rich, moist soil. During the flood the valley sides are widened and cut back nearer to the source of the stream. They flowed across the The Delaware gaps the Appalachian Mountains. cause of the rapidly sloping land. In The Potomac gaps the mountains at the place the flood-plains, which are nearly level where you see the rapids in the picture. Can you tell from the picture on page 84 in which direction the Potomac is flowing? The moun tains must have been a long, long time in forming, to have given the river time to cut through. There are rapids usually in a river where it cuts across the highlands. They are formed by the water flowing over the rocky ridge which has not yet been cut to the bed level of the river. If you build up a highland and make a plain on the sand in many places, it loses the power given table or in the schoolyard, and sprinkle it with water, you will see that the water will cut its way directly down the highland by the shortest way to the lower land. On the plain it will work A CITY ON A FLOOD-PLAIN, GERMANY. by the slope; so it flows in and out in long, swinging curves. Trace these curves or ox-bows in the pictures. curves. In the same way a river cuts a more direct course among the highlands be If you observe a carriage or a car go around a curve you will see that the wheels on the outer curve turn around many more times than those on the inner curve. This is because both wheels must get around the curve in the same time. The water in the stream flows much faster on the outer curve than on the inner. This causes the water which is moving so swiftly to cut away the bank on the outer curve, while it helps the slowly moving water on the inner curve to deposit the soil which it carries, as in the picture of a mud plain on page 83. Rivers often cut deep gorges in the rocky surface where there are few feeders to widen the valley. Describe the gorge in the picture on page 83. In countries where the weather is usually dry the river valleys are not widened as rapidly as in |