Small Towns, Wisconsin Southwest Region Fall 2015 | Page 12

the year is 400 million B.C. The land that will become Wisconsin is covered by warm, shallow seas. Layers of shell debris accumulate and harden into limestone on the ocean floors. Eventually the seas recede, leaving the rock behind. Seeping through the soil above the rock, rainwater and melting snow absorb carbon dioxide and become acidic. Then a large crack allows this acidic water into the limestone, where it dissolves the rock along its path! Thus, a cave is formed. At first, the cave is full of water. Eventually the water table drops below the level of the cave, and it fills with air. But surface water continues to seep through the soil and the porous limestone, drip…drip….dripping into the cave. Each drop contains dissolved calcium from the limestone, which is left on the cave ceiling or floor. Over the centuries these calcium deposits grow, at a rate of perhaps one inch per hundred years. Eventually, humans will discover this cave, and marvel at the fascinating shapes they find within. What will it look like in another thousand, ten thousand, or hundred thousand years? p.12 Small Towns, Wisconsin | 2015 Southwest Fall Edition | www.smalltownswisconsin.com | e. [email protected]