The Long Horn Caves, Marble Falls, TX

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Gregors head in the Chrystal Cathedral. stalactites

stalactites

The darkness here on the ceiling was created by bats.  Years before men started using it as hide-outs and tours.
  It is estimated that there were 300 bats per square inch.  The dark is from the dirt they brought back into the cave.
Dolomite walls and ceilings
dolomite and stalactites