Plate IX. Photograph of a cast made by pouring plaster over a surface of
mud in which ice crystals had formed, in Rock Island, Illinois, soon
after the ice in the crystals had been removed by slow natural
sublimation into the atmosphere, leaving open cracks in the mud. In the
locality where this cast was made, the crystals were relatively slender,
distant, and some gently curved, like those seen in Plate V. Slightly
reduced.
[Illustration: PLATE IX]