Resembling a huge Church Organ, this the largest and most pronounced of the calcite formations in the cave, is responsible for giving Organ Cave and the surrounding community its name more than a century ago. The Organ Cave System is formed in Mississippian Age rocks averaging 300-500 million years old. These rocks were formed from the shells and bones of Limy animals inhabiting a shallow inland sea called the Mississippian Sea. Over the ages, the bodies of these creatures were turned into massive beds of limestone and underlying shales. The principal cave forming beds are the lower zones of the Denmar formation.
Limestone has the property of being very soluble in weak acid solutions.
As rain water falls through the air, it picks up carbon dioxide and forms a week solution of Carbonic Acid. This acidic solution seeps into very small cracks in the limestone beds and dissolves out cavities along faults and joints in the rocks. As these enlarge, they join together to form Solution Channels. When these channels are large enough, they permit surface streams to enter them. The now free running surface streams hit the underlying Maccrady Shale and erode it away very rapidly, permitting the collapse of the Greenbrier limestone Cap rocks.