Photo: Mike Fender/Indianapolis Star/AP/Wide World OTHER MINI-LESSONS • Introduction: The Science of Caves • Visit the Paleolithic Cave at Lascaux • Caves in the United States • Sea Caves • Cave Animals

Most American caves are found in limestone rock. The caves began as water made cracks in the limestone and the cracks got bigger and bigger. The opening grew into underwater streams and rivers. When the water was gone, these underground waterways became cave tunnels and caverns. It can take from 10,000 to 100,000 years to make a cave that is large enough for humans to explore.

Water drips constantly in caves. The water carries minerals that accumulate into formations, as the water dries out. Cave formations grow over thousands of years.

1. Visit the cave map below to learn about caves near you. Print out the list of caves in the United States and ask each of your students (or, have them work in pairs) to choose a cave to learn about, from the Sea Lion Cave in Oregon to Crystal Cave in Pennsylvania.
2. Encourage your students to e-mail or write to the national park or other organizations that are responsible for caves and ask for information and materials.
3. Each student or pair should produce a tourist brochure for the chosen cave. The brochure can include a map showing the location of the cave, significant facts about the cave, and illustrations!
4. Make your own stalagmites and other cave formations in the classroom. You will need 2 cups hot water, charcoal briquettes, and Epsom salts. You may also want to use food coloring. Add one-half cup of Epsom salts to hot water in a shallow dish and stir. Then add the rest of the Epsom salts and stir the mixture for five minutes. Place three charcoal briquettes in the dish, and add a few drops of food coloring to the briquettes if you wish. Place the dish on a windowsill or in a corner of the classroom where it will remain undisturbed. Within four or five days, crystals will have “grown” on the briquettes.