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and 19th centuries. The canals were of major importance in the Industrial Revolution. They all included a lock, invented in the Netherlands in about 1373 and used on all canals ever since. The lock allowed boats to be raised or lowered around a weir or barrage.
Canals were very important
in America in opening up the country. By the end of the 19th century there were 6,500km of canals in America. They were very important in linking the Great Lakes to navigable rivers such as the Mississippi.
Canal building slowed with the introduction of the railroads, and many early canals have now been abandoned.
An artificial waterway designed to carry water for drinking, irrigation, and so on is called an aqueduct.
Chemical weathering
 Canyon—Look closely at this photograph of the Grand Canyon, and you can see the Colorado River flowing in the center of the picture. The river is nearly 2,000m below the crater rim.
Canyon
A steep-sided valley, usually in
a desert or near-desert area. The world’s largest canyon is the
Grand Canyon in Arizona, which is 360km long, 1.6km deep, and up to 50km wide.
Cataract
Another name for a series of rapids or a cascading series of waterfalls on a large river. The Nile in Egypt and the Paraña in South America both have cataracts.
Chemical weathering
The way that water and natural acids in the environment react with rock to turn the solid rock into soil.
 Chemical weathering —In this experiment two blocks of chalk are placed in a beaker. Vinegar is added. The chalk fizzes and begins to dissolve, passing into solution. This is a fast version of the chemical weathering that occurs in nature, where the dissolved rock can then be carried away even by slow-flowing rivers.
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