Mammoth Cave

11 April:  We started the day with a ride on the gravel bike path that generally followed the 9-mile route of the Mammoth Cave tourist railroad, which operated from 1886 to 1929.  The historical and geological informational signs, the varied terrain, and the redbud and dogwood in full bloom made for a pleasant ride, at least until Amy’s rear tire blew out on the return ride!

After lunch we took a self-guided cave tour down through the Historical Entrance and past the site of the nitrate mining operations, where some of the original equipment still remains.  The pipes conveying water to the leaching beds and then conveying the nitrate-rich leachate back out of the cave were made of hand-bored tulip poplar logs.  The labor for the mining operation was provided by slaves.  The reason the cave mud was rich in nitrates was the guano from bats.  Very few bats remain here today in this cave affected by white-nose syndrome.  Visitors exiting the cave walk over a mat saturated with detergent to prevent infecting other caves.

The passageway through which we walked was very broad, nearly level, and unadorned by any of the intricate formations we have seen in other limestone caves (they occur in other parts of Mammoth Cave, though).  The cave was sculpted by water seeping through limestone, but a cap layer of impervious sandstone has prevented a lot of vertical seeping, resulting in mostly horizontal flow through the limestone.  There are several roughly horizontal layers of passageways in the extensive Mammoth Cave system, with a few vertical connections.