Burt's Cave, near Maquoketa River, Jackson County, Iowa.

Burt's Cave, near Maquoketa River, Jackson County, Iowa.

Roof in Crystal Palace.

The organ, Manitou Grand Caverns.

Wind cave.

Piwyack Cave.

Piwyack Cave.

California, Yosemite Valley.- Tulool Weack Cavern.

Bower Cave, Yosemite.

Bower Cave, Yosemite.