Once the ancient subterranean stream cut its path through the limestone layers, marvelous formations named stalactites, stalagmites and flowstone began to form. These unique stone formations grow at an unbelievably slow rate: only about one cubic inch (about the size of a small ring box) will form in 100 years.
Howe Caverns lie in Coeymans limestone and Manlius limestone. 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 chooses 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 waterlime is the cream-colored rock that runs along the underground stream.
When rainwater seeps down through the soil above, it picks up a very, very small amount of limestone as it travels. In fact, there is only about a teaspoon of limestone dissolved in every gallon of rainwater that filters through the surface above the caverns. As this rainwater drips slowly through the cave's roof, the droplets of water evaporate, leaving behind tiny amounts of limestone on the cavern ceiling. In this way, stalactites grow downward from the vaulted cavern roof, particle by particle, over the course of millions of years.
The stone formations which grow up from the cavern floor are created in the same manner. Sometimes large droplets of water filtering through the cave roof don't have time to evaporate before they roll down a stalactite and drip off to the cave floor below. That's why stalagmites usually form directly below stalactites and continue to grow as more droplets fall from above. In some cases (such as the grand Pipe Organ formation at Howe Caverns), stalactites and stalagmites will actually grow together to form columns. (By the way, it's easy to remember the difference between stalactites and stalagmites. The word "stalactites" contains the letter "c" - like the word "ceiling." "Stalagmite" uses the letter "g" and so does the word "ground." Stalactites grow from cavern ceilings, while stalagmites grow upward from the ground!)
Flowstone is formed in much the same way as stalactites and stalagmites, except the water flows down the cavern walls. This wonderful rock formation resembles sheets of frozen, rippling ice. Other minerals in the water that carry the limestone give flowstone, stalactites and stalagmites their lovely colors. With the exception of the colors created by lights in the cavern, all of the colors you see at Howe Caverns are completely natural.
Rust-colored formations are caused by the presence of iron in the dripping water... green is from waterborne copper... grey indicates the presence of aluminum oxide... yellow comes from sulphur... and pure calcite makes lovely, milky-white formations.