Ancient Graffiti on the Ceilings of Mammoth Cave

In Kentucky we found the great Mammoth Cave National Park with its hundreds of miles of tunnels. On one of the many guided tours way down deep in the caverns and tunnels they showed some of the graffiti on the ceiling. No this is not recent tagging by vandals but markings by tourists and explorers in the early 1800s. They had no electricity but only torches for light so they could reach way up to the ceiling and write names and dates there.