National Geographic : 1953 Oct
© National Geographic Society + Naturalist Prasil in the Bat Cave Examines Guano for Insect Life Diggers extracted 100,000 tons of this nitrogen-rich fertilizer for citrus orchards. They left 6-foot seams of centuries-old guano layered between stone laid down by flowing water. This fresh material fell from the ceiling, where the bats sleep head down. Kodachromes by E. "Tex" Helm + Calipers and Ruler Measure a Fossil and the Skulls of Kindred Bats Left: This bat, falling on a stalagmite, became firmly cemented as the stone grew. Feet are buried; the head hangs down; wing bones show up darkly. Right: Fragile skulls and other bones accumulated in this graveyard as bats fell to the floor and died. ,~~ . ~~I , ~ i.