Слайд 6) 4. The Face of the Land

The framework of America is built around a huge interior lowland that has yielded some of the country's greatest agricultural and mineral wealth. It contains a large portion of its population and is the heart of what politicians like to call “middle America”. The region is drained by the Mississippi River and its great tributaries, one of the largest navigable river systems of the world. The Mississippi is the traditional dividing line between “East” and “West”. To east and west, the land rises to mountain ranges that flank the lowland to either side and separate in from the Atlantic and Pacific Oceans.

The Mississippi is one of the world's great continental rivers. It flows some 3, 970 miles from its northern sources in the Rocky Mountains to the Gulf of Mexico, making it one of the world's longest waterways. The Missouri is its chief western branch. Where the Missouri pours into the Mississippi from the west, it colors the river deep brown with small pieces of soil. Farther downstream where the clear waters of the principal eastern tributary, the Ohio, join the Mississippi, evidence of the difference between the dry west and rainy east becomes apparent. For miles, the waters of the two rivers flow on side by side, without mixing. Those from the west are brown because they wash away the soil in areas of sparse vegetation. The waters from the east are clear and blue. They come from hills and valleys where plentiful forest and plant cover has kept the soil from being washed away.

Like the Mississippi, all the rivers east of the Rockies finally reach the Atlantic; all the waters to the west ultimately flow into the Pacific.

The two great rivers of the Pacific side are the Colorado in the south, and the Columbia, which originates in Canada and drains the north The Columbia flows with quiet dignity.

The Rio Grande, about 1, 990 miles long, is the foremost river of the Southwest. It forms a natural boundary between Mexico and the United States, which together have built irrigation and flood control projects of mutual benefit.

North of the Central Lowland, extending for almost 994 miles, are the five Great Lakes which the United States shares with Canada.