Raccoon Mountain Caverns is located in a band of limestone from the Monteagle Formation, which formed during the Mississippian Period (approximately 320-360 million years ago), on the bottom of an ancient sea. In this sea, fragments and shells of various marine animals sank to the bottom and became compacted over time to form limestone rock. We have fossils of crinoids, coral, bryozoans, and echinoderms throughout our cave. Although fossils in the limestone tell us the age of the rock, they are not much help in determining the age of the cave. Most caves, including ours, are less than ten million years old. 

By the end of the Permian Period (about 225 million years ago), tremendous mountain building forces resulting from the collision of the continents forced the seas to retreat and pushed and folded the layers of older rocks high above the level of the sea. This produced the anticlines (rocks folded into an arch) and synclines (rocks folded into a “u” shape) which are now the Appalachian Mountains. Raccoon Mountain caverns is at the edge of the Sequatchie Valley which is one of the largest and most spectacular anticlinal valleys in the world.

Limestone caves are formed when acids attack and dissolve the calcite contained within limestone. This acid is usually carbonic acid (also known as soda water or carbonated water) which is formed when carbon dioxide combines with water. Most of the carbon dioxide comes from decaying leaves and vegetation in the soil. Scientists believe that most caves form below the water table by slowly moving water. After a rain, the rainwater mixes with the carbon dioxide in the soil and dissolves the limestone underneath.

Two factors control the formation of cave passageways: vertical and horizontal fractures in the limestone, and the water table. A cave is formed by water moving slowly in the small fractures below the water table. The rate of flow below the fractures changes as some limestone is easier to dissolve than others due to variations in composition. (This is evident at Headache Rock which is viewed along the Crystal Palace Tour.) Some channels grow larger as they take in more water and, as a result, they grow faster.

The cave forming process may take thousands of years and can be stopped by either the lowering of the water table or the formation of air passageways in the cave system due to surface erosion. As outside air enters the cave system, the water quickly becomes supersaturated with calcite and the dissolving process eventually stops. This change usually marks the beginning of the depositing of calcite in the form of stalactites, stalagmites, and other deposits known as speleothems.

Note: The above was taken from Caves: A Teacher Resource Manual. This 40 page illustrated manual is provided without charge to educators scheduling a cavern tour. The manual includes detailed information on cave formations, formation growth, environment, cave safety, and conservation along with classroom experiments and activity sheets.