About an equal distance further along the trail, the flow again breaks loose from the earth, bubbling up through gravel in an artesian fountain, the Boils. Beyond this, the stream remains invisible below ground, emerging for the last time nearly 2,000 feet away at Preston Cave before finally joining other streams on the long trip to the Gulf of Mexico. One of the unique features of the Springs is that it sits atop a large industrial plant unseen on the surface. More than 600 feet beneath where you are standing is a large limestone mine operated by Vulcan Materials. Limestone is used for cement, concrete, crushed stone, fertilizer and acid water treatment, among other applications.
Limestone is second only to coal as Kentucky's most important mineral product.
The reason is complex, but the numerous thin shale layers, originally mud on the bottom of an ancient sea bottom covering the Bluegrass, block the downward movement of the water. Probably other important reasons are the layers of volcanic ash that were spread across the region by volcanoes to the east during the formation of the Appalachian Mountains. These thin layers, far below the surface, contain a clay material called bentonite, which can absorb large amounts of water, swell and block the downward flow of water to the mine. Very little water moves all the way down to the mine. Culture History McConnell Springs as it appears today is as much a product of human intervention and modification as it is derived from natural forces.