(from an old postcard)

Western Kentucky's Mammoth Cave is the longest cave system on Earth, with 412 miles known and mapped as of fall 2017. The name does not refer to the early discovery of fossil mastodon or mammoth bones here. Rather, the name refers to the immense size of many rooms and passages.

Speleothem (= "cave formations") refers to all secondary mineral deposits in caves. Most speleothem is composed of calcium carbonate (CaCO3 - usually in the form of calcite, but sometimes aragonite). Calcareous speleothem is referred to using the rock name "travertine", a crystalline-textured, chemical sedimentary rock formed by precipitation from water.

Dripstone and flowstone are the most common forms of travertine speleothem. Dripstone forms by calcium carbonate precipitation from dripping water. Flowstone forms by calcium carbonate precipitation from thin sheets of flowing water. The most common forms of dripstone are stalactites (attached to ceilings), stalagmites (growing from the floor), columns (= fused stalactite-stalagmite pairs), and draperies (= curtain-like sheets formed as water drops descend along an inclined surface). Flowstone often has the appearance of frozen waterfalls.

In the vintage photo shown above, underlying breakdown rubble (not visible here) is being covered by a mass of flowstone and dripstone. These speleothem are forming at Violet City, at the southeastern terminus of Main Cave, the principal trunk passage in the Mammoth Cave Ridge part of the system. Main Cave has become erosively separated from the upstream continuations of the passage. The latter can be observed in Sandstone Avenue and Kentucky Avenue/Grand Avenue during the "Grand Avenue Tour".

Violet City can only be viewed during the "Violet City Tour", which starts at the cave's Historic Entrance and exits here at Violet City. The exit emerges from a sinkhole near the Carmichael Entrance. Violet City itself is a large breakdown pile that blocks Main Cave. Several sites in Main Cave have place names that include the term "City" (another example is Chief City). Such sites are large to enormous breakdown piles that led early tourists to imagine the remains of devastated cities.