Debra Bush, age 10, of East Peoria, Illinois, for her question:

How are hills made?

Every hill has its own story to tell and almost every story is different from all the rest. Some are young and some are very, very old. Some are still growing and some are shrinking. A few have lived gentle lives but most hills have known fiery volcanoes and shuddering earthquakes. In 100 million years, some of our hills will be lofty mountains and others will be lowly plains and perhaps even valleys.

The face of the. earth is restless and always changing. It takes ages for the great mountain chains to grow to their full height and for millions of years they are no higher than hills. When they are fully grown, the wind and weather wear down their tops. After more millions of years, they become little hills again. While the restless mountains are growing, volcanoes pour out lava that cools to form pointed peaks and hills. Glaciers also shift masses of dirt and rock. When they melt, this debris often stays behind in hills and rounded ridges.