How the Caves Were Formed: Limestone rock masses, slowly eroded by running streams, have magnificently transformed into the caves of Indiana. The surrounding land is characterized by sinkholes, underground drainage, sinking streams, springs and resurgences (streams which have run underground for some length then return to the surface). As rain water found its way into crevices in the limestone and mixed with carbon dioxide from the air, carbonic acid was formed. This solution of carbonic acid gradually ate away at the layers of the alkaline rock until holes were worn through. The resulting holes allowed the water to flow down among the rocks eventually forming an underground stream fed by rain waters. With time, these underground streams have ceased their water flow, but the hollowed out spaces remain as caves. The formations found in caves known as stalagmites (blunt, cone-like formations on cave floors) and stalactites (icicle like-formations on caves roofs) are also results of the carbonic acid solution dripping down into caves. The water evaporates, leaving a build-up of carbonate of limestone. Cave temperatures remain fairly constant year-round. The average temperature of 52 degrees (F) results due to the cave's "breathing". When the air outside at ground level is heated on warm days and becomes less dense than the cool air inside the cave, air "exhaling" from the cave forces this warm air up. This cycle continues, resulting in the cool draft often felt when approaching a cave. A reverse of this air flow takes place in winter months as the air inside the cave is warmer and less dense than the air outside. The cooler air is "inhaled" into the cave. A constant and complete circulation of air moves throughout the cave, with the change in season directing the flow.