Peter Yurowitz, age 13, of Brooklyn, N.Y., for his question:

What is a petrified forest?

Sometimes we use the word petrified to mean scared stiff. And a forest is­ a place crowded with living trees. Is a petrified forest a place of frightened trees? No, the trees of a petrified forest are turned to stone. For the original meaning of petrified is turned to stone.

In a petrified forest we seldom see any living trees at all. And we might fail to notice the petrified trees for they look like lumps of stone half buried or lying on the ground. These lumps of stone were trees maybe 60 to 100 million years ago. Slowly, slowly, the woody tissues were replaced with agate, jasper, opal and onyx.

The trees were petrified by running water. It stole the woody tissues and replaced them with stony minerals. Every cell was copied in perfect detail.

Our petrified forests are found in dry or desert regions. There are many stony copies of ancient trees in the Petrified Forest of Arizona. There are petrified trees around the Badlands of the Dakotas. There are petrified forests near the Columbia River and many other regions where ancient forests once thrived.