The walls of Howe Caverns consist of two types of limestone (Coeymans and Manlius) from different periods in the Earth's early history, as well as a rock known as Rondout waterred.
The Manlius limestone is seen most clearly and is the most abundant, while Coeymans limestone can be seen in the upper portion of the cave near the entrance. Coeymans limestone is more difficult to dissolve than the Manlius variety, so the water naturally chose a lower path through the Manlius layer. As a result, almost perfectly flat ceilings can be seen in parts of the cavern, which are actually the underside of the Coeymans limestone layer. Rondout waterred is the cream-colored rock that runs along the underground stream.
Scientists believe all of these rock layers were laid down by the ancient, extinct sea during the Silurian and Devonian periods of our Earth's formation. They are all sedimentary rock, formed by layers of deposits which settle out of a body of water and are then compressed into solid rock. To give you an idea of the age of these rocks, scientists estimate the Silurian Age began about 435 million years ago and ended when the Devonian Age began around 395 million years ago.
While there are a few fossils visible in the cavern walls, the main fossil beds lie in the layers of limestone above the cavern ceiling. This means the rock from which Howe Caverns is carved is older than most fossils. But the building process in Howe Caverns is never done! Nature is still hard at work in the great cave - as proven by the fact that we still hear, see and feel the droplets of water falling - and the cavern's face is always changing. It changes so slowly that the smudges left by smoking torches nearly a century ago can still be seen on the glowing flowstone walls today.