Onyx Pillars in the Mammoth Cave of Kentucky --
Frozen Niagara Entrance
The Onyx Pillars stand as sentinels guarding the passageway into the region known as the Onyx Colonnade. As glimpsed in thepicture this region abounds in unnumbered stalagmits and stalactites, ranging from the size of a quill to massive pillars, in one instance to a single pillar 22 feet in diameter. Brilliantly lighted - with electricity.