onyx and marble, among them a rare and beautiful onyx in black and
yellow. The coloring, tinting and banding of onyx seem generally to be
regarded as one of the unexplainable mysteries of nature, but is in
reality an extremely simple process that can be easily studied in any
active cave.

When the percolating acidulated water passes slowly through a pure
limestone it is filtered of impurities and deposits a crystal, either
pure white or transparent; if it comes in contact with metallic bodies
of any kind, it carries away more or less in solution to act as coloring
matter; the beautiful pale green onyx in several Missouri counties
taking its tint from the copper; in South Dakota, manganese in various
combinations produces black and many shades of brown; in both states an
excessive flow of water often carries a quantity of red or yellow clay
which temporarily destroys the beauty of exposed surfaces, but in after
years becomes a fine band of brilliant color.

Small wind caves are numerous in the Ozarks and being cold are
frequently utilized for the preservation of domestic supplies. The
entrance to one in the neighborhood of Marble Cave is high up on the
hill-side south of Mr. Powell's house and being visible from the porch
was too tempting to be ignored, and the walk up to it for a better view
was rewarded with a most charming bit of scenery as well. All the quiet
valley, divided by a rushing little stream, lay before us in the shadow
of early evening, while to the north and east the hills were brilliant
in summer sunshine, with one small open glade gleaming vividly among
the darker shades of forest green.

The cave was a very small room at the bottom of a steep, rocky, sloping
passage, and contained no standing water, although there had been a