Plate VIII. Photograph of a cast made by pouring plaster over a surface
of mud in which ice crystals had recently formed, in Rock Island,
Illinois, after the ice in the crystals had been removed by slow natural
sublimation into the atmosphere, leaving open cracks in the mud. The
comb-like ridges on the plaster cast have the form of the ice crystals.
Compare with Plate III.
[Illustration: PLATE VIII]