Where does chalk come from?

Saturday, June 11, 2011

Where does chalk come from?

Countless billions of tiny animals too small to be seen without a microscope live in the sea. Some of them have the long name of foraminifera. Under a microscope these tiny animals look like jewels. Each one has a shell which it has made for itself.

There are diferent kinds of foraminifera. They do not all make their shells of the same material. But a great many of them make their shells out of lime from the water. When these animals die, their shells are left behind and fall to the bottom of the water.

These little animals have lived on the Earth for many millions of years. In some places long ago they lived in such numbers that their shells made a layer hundred of feet thick on the floor of the sea. Then the bottom of the sea became dry land. The layer of shells became a layer of white rock. This white rock is a kind of limestone that we call chalk.

The famous white cliffs at Dover in England are made of chalk. There are layers of chalk in Kansas and other parts of the United States that are far away from the sea.


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A depressant is a drug that reduces the activity of various body functions. Some depressants such as anesthetics, sedatives, antiepileptics, narcotics analgesics, and some muscle relaxants, slow nervous and muscular activity by acting on the central nervous system. Tranquilizers are depressants that affect only part of the nervous system. They induce relaxation without causing total depression.
 
 
 

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